The Hazard Tree

Handbook

2nd EditionA guide to identifying and treating hazardous trees

Earl Kong

First edition February 2000

Second edition September 2003Copyright ! by the author

All rights reservedNo part of this book may be reproduced or transmitted in any form or by any means without written permission of

the publisher and author.

All photographs and illustrations by the author.

This book is dedicated to:Carol Kong

With thanks for your support.

Published by:Forestech LLC

260 Old Fort Townsend RoadPort Townsend, WA 98368

www.littleforest.org

INTRODUCTION

Trees are important to us, but they can be dangerous. Whether near a home, in a campground, or grouped together in a forest, any standing tree has the potential to be hazardous. It is imperative to remember that what may be normal and beautiful in a forest can be harmful when positioned along a path, in a yard, or in a recreational area.

In the wilderness, falling trees present no hazards; the tree failure occurs in its rightful place. It is only when in contact with human beings that dangers exist. Injury and death from trees and limbs falling on unsuspecting individuals or homes pose a very real problem. In order for humans to live in safety with their tree environment,

potential hazards must be identified and corrected, or avoided.

Incidents of injuries, deaths and property damage by failed trees are on the rise. As the population increases, human encounters with trees increase. When trees and forests had only occasional encounters with people and there were only a few homes in the woods, the chance that a failed tree would strike someone or their property was slim.

Today, more homes are being built in more forest remnants, and more people are visiting forests, parks, camps, and recreational sites. Failed trees are offered more targets more often.

Trees failing, and subsequently falling, are a normal and integral part of a functioning forest. Trees break, lean, lose limbs, get sick, become infected with insects, fall, and die. In the forest these failed trees provide habitat for wildlife, nursery for vegetation, and nutrients for the soil, and a vast array of life flourishes as a result. Failed trees also allow sunlight to penetrate the forest canopy, energizing the forest floor. Contact with human beings does not alter this cycle but causes an unnatural disturbance and has a negative impact on the system. This natural event can become a destructive force when failed trees destroy homes and other structures or strike humans.

Normal trees become hazardous as a result of their encounters with outside factors such as weather, insects,

pathogens. In addition, soils, topography, and people influence how trees behave. The theory of hazard tree management is based on an understanding of the physiology of trees and their relationship with adversarial forces such as those listed above.

Tree physiology is important because a tree’s basic structure greatly influences its balance and therefore plays an instrumental role in whether a tree fails or remains standing. If, for example, a healthy tree loses a branch in a storm, then its balance is weighted to the other side. The tree will ultimately grow new branches and foliage to recreate its balance, but for a brief time there is some instability.

Tree pathology is also important because any decay in a tree weakens its structural integrity. Once a pathogen invades a tree’s structure, it will affect that tree for as long as it stands. Trees do not have any healing capability.

The properties of the soil are important because it is the medium that provides the trees with life-supporting water and nutrients. Furthermore, the soil is what the tree grabs onto when threatened by storms. Weather is important because, other than humans, it is the single most challenging factor trees face. Insects attack trees. They eat the foliage, raise their young in the bark, wood, and in the tree’s cavities, and their young girdle trees from feeding. Fungi attack and can cause decay anywhere on a tree. From its roots to its leaves or needles, mechanical injury is an important factor because it exposes the tree’s fibers to fungi and decay. Topography influences a tree’s development because where a tree grows (for example, on

the top of a hill versus the side) determines its weather exposure.

Failed tree accidents are somewhat preventable. After a storm there is usually a lot of damage from failed trees, but prudence in a community can minimize these damages. A severe storm can knock down parts or all of even a healthy tree, and nothing can be done to prevent this. But wind or storm of any degree is much more likely to cause failure in sick or defective trees. Very weak or dead trees can even fail on perfectly calm days. Calm day failure is irresponsibility at its worst because such an event is totally avoidable.

When a tree begins to lose strength as a result of one or more adversarial relationships, it usually presents signs that a well-informed person can interpret.

This book presents information on recognizing and interpreting those signs and how to incorporate them into a damage and injury prevention program. Correcting a hazard tree situation before an accident occurs is crucial to protecting ourselves, staff, invited guests, and the public.

The Hazard Tree Handbook is vital reading for:

!Recreation site managers, who should have information about the health of the trees at the sites they manage, thereby protecting their guests, and protecting themselves from liability;

!Government officials, who should have knowledge about hazardous trees before making rules about trees they manage or regulate;

!Homeowners, who should know if the trees within striking distance of their homes are defective, and consequently hazardous;

!Outdoor enthusiasts, who should know the difference between a healthy, normal tree and a defective, hazardous tree, for their own protection.

This second edition is updated with more comprehensive information including a glossary and lists of trees’ relative shade tolerance and expected mature heights.

As people live closer to the forests and use them for recreation and aesthetics, it becomes more important for camp managers, homeowners, and recreation enthusiasts to be informed about what makes trees less than safe. Readers will learn how to differentiate between a healthy tree and one that is defective and dangerous; to interpret which trees have the potential to cause harm and act before they do. By using the information learned, people can enjoy trees and forests safely.

“Research”

Thanks to:

Arron KongJon Guyton

Laura HoughtonMark Larson

Jan MilliganRick Reid

Chuck StewartJ.W. Turner

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Tree failure is a natural part of any functioning forest

This does not change because of the presence of people.

About the Author

Earl Kong has over 25 years experience studying and working with the forests of North America. After graduating from Oregon State University in 1975 with a Bachelor of Science degree in Forest Management, he completed an internship with the Bureau of Land Management studying forests, tree structure, insects, and

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diseases. Since then he has worked as a timber cruiser, timber sale administrator, and forest manager. Currently he acts as a natural resource consultant for managing forests and trees with respect to human concerns and safety. His article "Hazard Tree Management for Camps" appeared in the September/October 2002 issue of Camping Magazine.

CHAPTER ONEThe Normal Tree

A hazard tree is a defective tree standing where it could harm someone or damage something with value, if it fails. Trees growing in a forest and those growing among humans and their property must be differentiated.

In the forest, as a functioning unit, everything is normal – not just health, but also all weather patterns, pests, disease, and death. For example, a disease known as laminated root rot kills groups of Douglas fir, giving other species an opportunity to grow and encouraging the forest to diversify. This disease, in a forest, is

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normal. It results in a negative outcome for individual trees but has an overall positive effect on the forest.

Diversity is not the only possible positive result. Fallen dead trees provide natural habitat for animals and allow more sunlight to reach the forest floor, energizing that portion of the forest and encouraging rapid growth among the smaller trees and shrubs. The decomposition of trees attracts insects which in turn provide food for other animals. Some trees have the capability of absorbing atmospheric nitrogen and changing it into a compound they then inject in the soil for other trees’ use. The nourishment of the soil that occurs through these two processes encourages the proliferation of insects and plants, such as fungi and berries, that wildlife depend on. This forms the base of a life and food chain that extends up the ladder to human beings.

This same laminated root rot, when it attacks trees growing near human concerns, is abnormal and dangerous. It kills trees’ root systems, thereby destroying their anchoring mechanisms and making them highly susceptible to wind throw (tree failure caused by wind). The failure that occurs in a forest is an agent of growth and diversity; failure occurring outside the forest has injured people and damaged buildings.

The life cycle of a tree can be described in four stages: juvenile growth, mature growth, over-maturity, and death.

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Juvenile Growth – 0 to 30 years

The juvenile tree is generally plastic, healthy, and fast growing. Defects have not had a chance to affect its strength to hazardous levels, and it doesn’t carry enough mass to cause severe damage if it fails. At this stage, the tree begins to adapt to and develop defenses for the weather conditions it is exposed to on a regular basis.

Mature Growth – 30 to 60 years

The tree becomes more rigid, with more mass. It takes on the appearance characteristic of its species if no external factors have affected its structure. If it has been affected by outside factors it may display evidence of those encounters. Breaks will show scars even after they have callused over. If pathogenic activity is present, it will likely have had a chance to affect the tree’s structure. Defenses, such as callused tissue or extra fiber, used as a weapon against outside factors are more pronounced. From this stage on, any interference to the normal function of the tree creates increased potential for failure.

Over-Maturity This is the stage in which most tree hazards occur. The tree has enough bulk to cause major damage to people and property. The more distorted and picturesque the tree, the more defects it contains and therefore the more hazardous it is. The sculptured look is created from broken branches that grew back distorted, crooked boles that are the result of storm damage, infections by

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pathogens, and bulges caused by the callusing over of wounds. The tree’s branches begin to die, its root systems begin to fail, and defects and their associated decay have had enough time to reach their most hazardous level of weakness to the tree’s structural integrity.

Death

Average tree life span varies with species, ranging from 70 years to 1,000 years or more. A dead tree is dangerous because its fibers are deteriorating. A tree can die while still standing or it can fail and die. It dies from disease, insect attacks, or damage by people, or through a combination of these factors. Insects or people can injure a tree, opening a venue for fungi to finish the job. Quite often, a tree dies from disease contracted during the juvenile growth stage.

The concept of the “normal tree” only refers to trees that have the potential to damage human concerns. The normal tree is a healthy tree with no defective components. There are no diseases, missing parts, or abnormalities present. Its roots are healthy and have sufficient soil and water to obtain nutrients. It is growing at its normal potential and does not lean.

As the normal tree grows, it expands outward evenly and concentrically, adding new fibers for strength and size. It adds fiber first to the lower bole (where the bole and limbs meet the earth) and roots, where it most needs stability and structural strength. The tree then

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distributes fiber around the perimeter of the bole, nodes (where branches and bole meet), and limbs. The branches are also distributed around the tree, and the foliage around the branches.

Visibly, the tree’s appearance is characteristic of a member of its species. No external defects such as holes, wounds, unusual bulges, spike limbs or knots, crooks, or sweeps can be observed. A normal tree stands erect and perpendicular to the earth; its bole (stem) is proportionally round, symmetrical and straight except where the limbs connect. It is well supported at the lower bole. The angle and form at which the limbs are growing are characteristic of the tree’s species, as is the shape of the crown. The tree’s foliage is full and of a color typical for its species.

Some species do not grow tall or with only one bole. It should be remembered that there is no ideal tree shape; the important factor governing whether or not a tree is considered normal is whether its appearance is in a normal range for its particular species.

External factors such as wind or light source can modify a tree’s appearance. Trees grow in response to the amount and strength of wind they receive. They also grow toward light, so their shape can be affected by which direction they receive light from.

Trees are inherently adapted to occupying a certain position in a forest. Trees that dominate the upper canopy are adapted to full sunlight, and those occupying the lower levels of the forest are adapted to shade. Trees

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occupying the intermediate levels of the forest are adapted to growing in intermediate light, but they can adapt to either full sunlight or more shade. The trees growing in the dominant layers do not function well in shade; likewise the trees in the understory do not function well in full sunlight.

Trees adapted to light will often be weak in appearance when growing in shade, with color less robust than their counterparts growing in sun. However, trees are hardy and adaptable, and having too much or too little light alone does not determine whether or not a tree is considered normal. Some weakness is acceptable, but a tree receiving much less or much more sunlight than its species requires will grow unsound. Any deficiency that significantly affects a tree’s appearance results in a less than normal tree.

The normal tree, as the standard of health and structure for trees, is the basis for measuring tree hazards. Any significant deviation from the normal tree as previously described may indicate instability and a higher potential for hazard.

Buttressing is an adaptive technique normal trees have acquired in response to wind exposure. Trees develop buttressing as a way of reducing or preventing failure from wind. The more wind a tree receives, the more buttressing it develops over time. The converse is also true.

Swaying in the wind triggers the growth of extra fibers in a braided pattern that makes them difficult to

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separate. The extra fiber at the tree’s base, where the lower bole meets the ground, helps the roots support the rest of the tree. During a storm, this is the area that receives the most stress. The above-ground portions of the tree sway and bend to dispel wind before it reaches the roots; the roots fight wind by standing erect. These two approaches intersect where the bole meets the root system at the ground surface. This area is the last zone of resistance before any above-ground failure occurs.

In a group of trees, buttressing is usually developed only by those growing on or near the periphery; those growing on the interior, protected from the wind, do not need it. In some cases, the interior trees receive enough wind to develop buttressing. Topographic relief can expose some trees to sufficient wind to cause them to need the extra support.

A normal tree that is suddenly exposed on a regular basis to winds it has not developed buttressing to withstand should be considered a less than normal tree for a while. If it receives low velocity winds at first, it has a good chance of developing resistance. But if it receives severe winds right away, its probability of experiencing wind failure is very high.

Extra fibrous growth or bulges in places on the tree other than the lower bole or nodes may indicate interference with the tree’s functions by outside forces or the callusing over of a wound. While it is true that trees have no true healing ability, they will form calluses over wounds or infections by adding fiber over them. Extra fiber or buttressing observed on a tree that is not

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exposed to wind may indicate pathogenic activity in that area of the tree. The tree may have added the extra fiber as a defense in its battle with a disease.

Normal trees can show blemishes on their boles and continue to be sound. On areas where limbs have been broken or pruned, the tree begins to callus over the wound. The area will ultimately be hidden and appear smooth with perhaps a slight bulge. If a pathogen infects the wound, the area will appear abnormal. A hole may be present, indicating decay infecting the tree’s bole. In some cases, the hole or infection may be callused over by the tree, but an abnormality such as a seam may result where the bark has joined after the callusing over is complete.

The hallmark of a normal tree is symmetry. It will look even on all sides provided that it is receiving sunlight evenly. Whether standing alone or in a group, trees tend to achieve symmetry as long as light, water, and nutrients are available regularly and in sufficient quantities.

The symmetry achieved by a single tree differs from the symmetry achieved by a group. A single tree achieves symmetry by adding fiber and foliage evenly on all sides as it grows. A group of trees achieves symmetry by adding fiber and foliage to the outside edge of the peripheral trees, achieving group symmetry with asymmetrical individual trees. As long as the group remains intact all the trees should be considered normal.

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An asymmetrical tree can be considered normal as long as it continues to function in its normal developmental space. Removal of some of the trees or other interference disturbs the group’s balance. The remaining trees are no longer functioning in their normal role and can become susceptible to failure. Such trees would no longer be considered normal.

Whether in a group or standing alone, an overall symmetrical look indicates good health. Lack of symmetry is an indication that something, such as missing branches or the removal of a neighboring tree, has interfered with the tree’s normal functions.

If two trees have been growing together and their crowns are overlapped or intertwined then both trees’ crowns occupy and share the same space. The removal of one of the trees will result in an asymmetrical tree remaining. Both trees developed shared resistance to wind, and the removal of one leaves the standing tree unprepared for the winds both resisted. If it does not fail first, the remaining tree will grow stronger until it has adapted to standing alone, achieving its own symmetry in time. This is an indication that it has adjusted itself to receiving and resisting or absorbing the same winds.

The amount of time needed to adapt back to symmetry differs by species and the age of the tree. Younger trees adapt more quickly while older ones take longer.

Most normal trees will develop defects at some point in their lives, becoming a victim of such things as mechanical damage or disease. A minor injury sustained

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early in its life can develop into a serious defect by the time the tree reaches maturity. In most cases the tree will, in time, successfully callus over a wound and infection, hiding the defect. When this happens it may take a trained, experienced forester to identify such defects. Failure secondary to damage from storms, wind, and lightning is also a common event in a tree’s life. Any event that changes the natural structural composition or health of a normal tree will increase the likelihood of the tree’s failure, thereby placing it into the category of hazardous.

Suppose a branch of a perfectly healthy normal tree dies or breaks. Does this disqualify the tree from being considered normal? It depends. If the break is large enough to expose the tree to pathogenic activity, then the tree can no longer be considered normal. If the tree is within striking distance of human activity, it should be monitored. The tree may present no threat at first, but monitoring will allow the present or future owner or property manager to establish the potential for future threat.

Breaks of less than a few inches in diameter occurring on small branches far from the tree’s bole are minor damage and are unlikely to have any long-term effect on the tree. The danger with breaks or wounds is that if the tree’s fibers are exposed, airborne pathogens can infect the wound and continue to cause decay until the structural capacity of the tree is weakened.

If a branch breaks off some distance from the tree, chances are that even if the wound gets infected, the

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resulting decay will not reach a significant portion of the tree’s main structure. Furthermore, the branch may die, and decay generally does not spread through dead fiber. Of course, if a tree continues to lose a substantial amount of branches over time, it would be prudent to investigate why. Sometimes a dead branch indicates disease or failure somewhere else in the tree, such as the roots or bole.

Suppose a tree acquires a wound to its bole from mechanical means or from natural causes such as another tree falling and wounding it. If the wound is superficial, only removing bark, for example, then the tree can still be considered normal. However, if the wound exposes fiber in the tree’s bole there is a risk of pathogenic activity directly related to the size of the wound. At the very least, the tree must be considered a low level hazard, if only because of the uncertainty of its future condition.

From a hazard tree standpoint, the normal tree’s potential for failure is strictly a function of the weather and the tree’s resistance against that weather. By definition, there are no defects, no past damage, no pathogenic activity, and no mechanical damage to affect this relationship. The normal tree can be addressed as one that is generally safe to encounter in places where humans are generally expected to go. It has the highest probability of remaining erect during a storm. However, it should be remembered that even perfectly normal trees can simply be overwhelmed by severe weather and fail.

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CHAPTER TWOFactors Affecting The Normal Tree:

Bole And Foliage

The same factors affecting trees in the wilderness continue to affect them when human beings and their concerns are present, with one addition: humans themselves. We create many of the factors that cause trees to become less than normal.

Adaptation

Trees adapt to their environment and to the events that affect them. Weather, disease, and mechanical damage are all examples of adverse conditions that require responses from the trees they affect. Trees have natural defense mechanisms that allow them to respond to and counter such conditions in self-protective ways.

Trees have two ways of adapting to their environment: over several generations (genotypic adaptation) or

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throughout their own lifetimes (phenotypic adaptation). Genotypic adaptation is a product of evolution. All trees vary within limits set by their species. Certain variations prove to be advantageous in certain settings, allowing the trees with those variations to survive and pass their genetic characteristics on to the next generation of trees through their seedlings. Over time, those genetic characteristics will dominate the trees in that area. Phenotypic adaptation is an individualized process whereby trees respond to the particular stresses they have encountered.

Weather conditions are a constant, ever-changing stress to which trees must adapt. Certain species have adapted to and are capable of withstanding more winds than others. In areas where strong winds are common, those species that are prone to wind damage tend to fail and drop out of the system or grow in the understory, protected by trees capable of withstanding these winds. Those trees growing in the forefront of regular winds continue to develop protective characteristics, such as buttressing, growing additional fiber at the junction of branches, adding pitch or other lubricants in areas where bending causes fibers to rub against each other, or developing plasticity in their fibers.

Trees that have not been excessively exposed to wind, such as those growing in the interior of a thick forest, do not develop the kind of structure necessary for wind resistance. If, as a result of human interference, they suddenly become the trees on the edge, they are made vulnerable to wind failure.

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Trees that receive mechanical damage will callus over the wound using special fiber with harder cell walls designed to contain infection. If pathogens infect the wound, the tree will attempt to callus over both the wound and the infection, sometimes successfully. The disease will continue to deteriorate the fibers of the tree while the tree continues to add fiber around the infection. The event becomes a contest between the tree trying to outgrow or contain the infection and the infection trying to deteriorate the tree’s fibers. In most cases, the tree will be required to produce extra callus-type fiber for the remainder of its lifetime because the infection will never go away. Sometimes the only indication of infection inside a tree is a bulge where the extra fibers have been added or a seam where the callusing over is almost complete.

The decay will always be present, and the disease will always try to escape containment, sometimes successfully. It is sometimes a low-level hazard, but depending on the severity and the location, it can be a significant problem. A small amount of decay on the bole of a tree receiving large amounts of wind is more significant than the same amount of decay on a large tree that is not exposed to severe winds.

Decay and defects should be noted and monitored for future hazard potential. The purpose of monitoring is to establish the tree’s base condition against which its later appearance can be compared. The possibility always exists that the disease will reemerge, and since we cannot see inside the tree, we cannot see the extent of the secondary damage. Significant decay will be

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reflected in the crown, which can be monitored. Reduction in the crown closure indicates a problem somewhere in the tree; however, it cannot be assumed that the problem relates to the wound. It is never safe to assume anything about trees; a tree can have more than one defect affecting the crown’s appearance.

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Height

A tree’s height is an important factor in its ability to be a hazard. Tall trees require more diameter for support than short trees. Because of this required larger diameter, they weigh more. Considering that trees accelerate (gain speed with distance) when falling, taller trees are moving faster when they strike. Because of their height, taller trees cover more distance when they fall, giving them a greater range of targets. This combination means that taller trees have increased potential for risk as well as damage. They are the trees that should receive additional scrutiny, attention and care. The havoc wreaked by tall trees is quite significant compared to the damage done by short trees.

The factors that determine a tree’s height are its species, the quality of the soil it grows in, the amount of water and light it receives, and the amount and kind of nutrition it receives. All species are predisposed to a certain height and rate of growth. Manipulating the other factors can change the actual height of an individual tree but not beyond the potential for its species. When designing a landscape, it is important to consider the species and therefore the potential height of trees planted or retained near structures or places frequented by people. A tree with a potential height of 150 feet will soon be a threat to a nearby structure if it is planted only 50 feet away. A tree with the potential to grow to 150 feet should be planted 150 or more feet from a structure so it will never threaten that structure.

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Sometimes non-native trees are planted in an area where they may fare better or worse than in their native environment. A tree genetically predisposed to grow to 100 feet in 50 years in ideal conditions may only grow to 50 feet in less than ideal conditions. Factors causing this decrease in the tree’s growth are too little or too much water, soil compaction, too little light, insufficient rooting space, and lack of nutrients. These are generally factors that we can control. Providing the ultimate conditions for any species of tree can help a tree achieve its potential, but it will never exceed its genetic potential.

Soil

The soil contains the tree’s nutrients and most of its water. It is also the most convenient factor to manipulate. Manipulating light exposure requires drastic measures like cutting down or growing other trees in the vicinity. Without changing the soil’s structural makeup (by plowing for example), adding water and fertilizer are the most convenient ways of affecting the soil and consequently a tree’s growth. However, too much water can restrict a tree’s growth through suffocation of the root system. There has to be a certain amount of air or gases between the upper layers of soil and the atmosphere. Trees’ roots depend on this exchange of gases as the roots/soil relationship is an aerobic function in the upper layers of the soil.

Foliage

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In some cases a tree's foliage also takes up nutrients and water. The sequoia of northern California is perfectly adapted to the region’s fog belt, and its needles take in much water from the air, allowing the tree to grow among the tallest in the world.

Even though a tree develops proportional strength to support its given height, the taller a tree grows, the more external forces, such as wind, it is exposed to. It has more wind catching “sail” and more limbs and foliage to retain ice and snow. Tall trees can grow above other trees and/or structures and consequently become exposed to additional weather factors. This additional exposure and the associated growth increase the likelihood of the tree’s failing, so tall trees should at the very least be monitored for changes in their condition.

Crown

A tree’s crown is the area containing the branches, fruit, and foliage. As they fall and decay, the leaves, small twigs, bark, seed, and fruit account for most of the nutrients in a forest soil available to the tree. Other than genetics and illness, light is the major contributor to the pattern and shape of a tree’s crown. This is where energy production takes place, where the tree combines sunlight with water and nutrients from the soil to produce energy and new fibers for growth and for structural stability. Not all areas of the crown produce energy efficiently. The lower, older, and shaded areas of the crown produce energy and new growth, but mostly for their own maintenance. This should be an important consideration when thinking about a pruning project.

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Other variables that affect the health of the tree also affect the crown’s pattern, but the amount of light and the direction of that light most affect its shape and strength. A tree that is genetically predisposed to growing in full sunlight will grow weak and not thrive if grown in shade. A tree growing against a structure will not develop foliage next to that structure because it receives no light from that direction; conversely, it will grow extra fibers and foliage on the side receiving more light. Trees growing in a thick forest will have very narrow and thin crowns since the only light they receive is at their uppermost reaches. A tree growing with no close neighbors will grow thick and wide foliage with large branches because it receives sunlight from all directions. Trees that are genetically predisposed to growing in shade can sometimes do well in full sunlight as long as they have had the opportunity to adjust over a period of time. But trees genetically predisposed to growing in full sunlight will ordinarily not thrive in shade even after having had time to adjust.

The Bole

A tree’s bole, or trunk, is the portion that supports the limbs and crown. The bole starts just above the roots and continues up through the crown to the leader in conifers. In hardwoods the bole continues until it branches out and ordinarily stops where branches are at least its equal in diameter. The bole’s size and shape are determined by species, age, light, and competition from other trees and defects.

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Given a certain species and age, water is the greatest factor affecting the size and shape of the bole. The amount of light a tree receives is influenced by competition from other trees or structures. For example, trees growing in a dense forest receive most of their light from directly above; other trees block the sidelight. Those trees will grow with shallow, narrow crowns. Trees growing in open spaces, on the other hand, will produce large wide crowns with large wide boles and side branches as they receive a substantial amount of light from all directions.

Wide boles are inherently stronger, having more bulk and more fiber. This is usually necessary because the factors that produce a wide bole also produce a larger crown and branches resulting in a more substantial “sail” and requiring much more strength, not just for support but also to resist storms.

If exposure to storms is the primary hazard factor, then a tall slender tree has a greater probability of breaking off than a short, stout tree. Any increase in the diameter of a tree’s bole increases its strength, and any increase in height increases the stress on that bole. Thus the taller a tree grows, the greater the strength and diameter necessary for that tree to stand erect and resist storms. As long as a tree has the bole strength equal to or greater than the support its height needs, it will stand on its own. But when storms challenge the tree anything can happen. Any tree can fail if it becomes overwhelmed by nature.

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The thickness of the tree stem is a key factor concerning its potential for failure. A standing tree receives a certain amount of stress from wind and other weather factors. How this stress is distributed determines whether a tree fails or not. When windstorms approach a tree their first encounter is with the foliage. The foliage absorbs some of the wind energy through bending or trembling. The energy not absorbed by the foliage is passed on to the twigs and small branches which absorb what they can through swaying and bending. What does not get absorbed is passed on to the larger branches which bend to absorb what wind energy they can and pass any additional energy to the bole which has sole responsibility for absorbing the rest of the energy. If the bole receives more energy than it can absorb through bending then it fails. The roots can absorb a small amount of wind energy, but it is the bole that is the last vestige of wind energy absorption before failure. Whatever energy passes from the bole to the roots is combated by sheer resistance. Roots and soil don’t bend; they hold firm.

Stem thickness has a positive effect, offering more resistance against wind by passing more wind on to the roots. However, the roots and soil have a limited capacity to absorb stress which varies with weather. Any time there is more stress than any particular segment of the tree can absorb or pass on, failure occurs in that segment. Failure of whole trees occurs when more stress is passed to the roots and soil than they can withstand.

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The size of a tree’s bole is a function of species but is strongly influenced by the size of the crown it needs to support. Decay and defects reduce the bole’s strength and in doing so counter the tree’s inherent design by interfering with the tree’s normal functions, such as normal growth patterns.

Bole or stem disease increases the probability that a tree will break off. Disease deteriorates the tree’s fibers and, therefore, its strength. For example, if a tree capable of withstanding a 50-mile per hour wind gets infected, then over time less and less wind will be required to cause failure. Bole disease is usually a wound infected by airborne pathogens, which subsequently becomes internalized into the tree’s functions.

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The Sail

The sail, defined as the wind-catching capacity of the tree, has a direct relationship to the tree’s potential for failure. The greater the amount of wind intercepted by the tree, the greater the potential for failure and, therefore, the greater the amount of strength needed by the tree to remain standing.

A tree’s crown receives almost all the wind that challenges its structural integrity. The bole receives a small percent of such winds and is considered a part of a tree’s sail, but it’s the crown that is responsible for receiving winds, and it is the crown that can be modified to reduce the amount of wind affecting the tree. Storms and wind will vary in intensity on their own. We have no control over this. A tree’s crown can be modified to determine how much of a given storm will be received and therefore threaten the tree. Tree crowns can be modified to catch less wind through pruning or topping.

The sail effect of the crown is a relationship between the surface area of the crown and the amount of crown closure. The denser the crown, the more efficient it is at catching wind; conversely a thin crown is less efficient at catching wind because a portion of the wind coming at the tree simply passes through the crown. This is an important concept to consider when using pruning as a tool to reduce the wind-catching capacity of a tree’s crown.

The surface area is the total area affected by wind, and the crown closure is the density or thickness of the

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crown. The surface area of the crown determines the potential amount of wind that can be captured by the tree, and the crown closure determines the amount of wind that will pass through the crown and the amount resulting in stress on the tree. A dense crown receives more stress because it allows less wind to pass through it, passing more stress on to the bole. A thin or less dense crown passes less stress on to the bole because it allows more wind to pass through.

Arrangements

Tree arrangement is the pattern made by more than one tree. Arrangements manipulate the effectiveness of winds. Arrangements can change wind direction, create channeling, intensifying the wind’s effect, and can also block the wind, creating a safer area. A tree that is in a position to affect the arrangement of winds is also positioned to receive the brunt of the weather. Consequently, those trees may have a higher potential for failure, unless they have survived long enough to have adapted to the circumstances.

A tree’s potential for failure is closely related to its spatial relation to other trees or objects. Several trees in a clump can literally hold up trees that would have otherwise failed. The arrangement of the trees and their relative location can determine the velocity and direction of the wind that neighboring trees receive, and consequently the defense mechanisms that each tree develops. Trees develop defenses only to those events that they are exposed to.

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In a stand of trees, changing the arrangement by removing one or more of the trees causes the remaining trees to receive stress they have not been exposed to and, therefore, have few defenses against. For example, a tree accustomed to getting winds from the north develops defenses for a north wind. If the same tree suddenly receives strong winds from the east, then its probability for failure increases because it is being exposed to factors not previously experienced and therefore has not developed defense mechanisms against.

Lean

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Fig. C

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A discussion about leaning trees must include the normal or vertical tree. The normal tree’s center of gravity splits the bole in half vertically; its weight simply is mass and gravity. The only force the normal tree exerts is weight. The force of the tree pushing down and the force of the earth pushing back are equal, the tree maintains equilibrium and is stable. Gravitational forces are working to keep the tree vertical.

The center of gravity for a leaning tree is not in the center of the tree’s bole; it changes depending on the degree of lean. The force of the leaning tree depends on the weight of the tree, the height of the center of gravity, and the angle of the lean. Leaning trees create a constant stress on the root systems. This stress increases with the added weight of snow, ice, or rainwater. (See illustration on page 87)

A leaning tree is already predisposed to failure because the force of gravity works towards its failure instead of towards its stability as with the normal tree. In addition, there is the added stress of the change in the balance that the tree has previously adapted to, particularly the root systems. Ordinarily when a previously vertical tree changes to a leaning tree, the root system has been disturbed and no longer serves the tree adequately as an anchoring system. Most likely the soil-holding relationship with the roots has been broken and actual trees’ roots have also been broken.

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A slight lean can cause substantial horizontal force. This force is only countered by the strength of the roots holding the base of the tree down. There is constant stress against the roots. To complicate matters more, no two trees are exactly alike. Add to this weather, wind, rain, snow, and ice, and more force is placed on an already stressed situation. The weather also affects the holding capacity of the soil, which in turn affects the ability of the tree to use its roots/soil binding capacity.

The amount of time that a tree has spent leaning is also a key factor in its stability. As much as possible, a tree makes corrective growth in its root system, bole, and crown so that in time the center of gravity will approach achieving balance again. The balance may not be through the center of the bole, but balanced all the same. A leaning tree will grow its leader and branches back toward the base of the tree, and its roots will grow out in the direction of the lean. Ultimately, the center of gravity will bisect the tree, dividing its weight proportionally for balance. There are limitations to this corrective adaptation, however, based on the severity of the lean.

Disease

Trees that have been invaded by a pathogen will sooner or later show the effects of that invasion if the tree is unable to contain it. Diseases in trees usually show a symptom or sign of their activity such as abnormal or reduced growth, color change, swelling, or wilting. Fruiting bodies such as conks on a tree or certain mushrooms on the ground around the base of a tree are

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also signs that disease has invaded a tree or a stand of trees.

All parts of a tree are susceptible to disease. Pathogenic spores are present in the atmosphere and soil, waiting for the opportunity to infect trees through wounds or cut surfaces.

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CHAPTER THREEFactors Affecting The Normal Tree:

Root Systems

A tree is dependent on its roots throughout its entire lifetime. When young, a tree’s most important task is to develop a strong root system; without one to obtain nutrients and water from the soil, its foliage will not thrive, and the tree will die. The roots, in combination with the soil, provide the last venue of resistance a tree has against wind as stress is transferred down the tree. Their responsibility is to stand firm and hold the tree erect, and to defend the tree’s structural integrity from the challenges of storms. Depending on the cause of death, the roots may even hold the tree up for a while after it has died.

Root Pattern

A tree’s root patterns are determined by its species and the soil surrounding it. The two types of root systems,

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determined by species, are taproot and fibrous. A tree can also have a combination of the two. In a taproot system, the tree produces one central root that penetrates the soil vertically and spreads out at a depth determined by genetic predisposition and the composition of the soil. In a fibrous system, there is no central root. Instead the roots spread out from the beginning, just under the surface. The depth and design of individual roots is determined by the soil. Although a species of tree may normally have a taproot system, if the soil does not have the depth to accommodate such a system, it will force the roots to develop a different pattern. The roots adjust their structure to accommodate the strongest combination possible between the roots and the soil, making the best use of what the soil has to offer.

Fig. 19A

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Fig. 19B

“Restricted Root Development”Even though some trees are genetically predisposed to send deep roots, the soil can restrict and influence root development.

Compaction

The roots need a certain amount of air among the soil particles to function properly. The exchange of air and gases between the atmosphere and the soil is necessary for creating a healthy medium in which the roots can acquire the water and nutrients they need. Compaction is the removal of air spaces in the soil which restricts the movement of water and the exchange of air with the atmosphere. Compaction changes the function of the soil and its relationship with trees’ roots. The source of compaction is human activity, such as the construction

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of roads and trails, recreation, and any kind of human activity that occurs around the base of a tree. When the soil is compressed, it packs tightly around the roots, suffocating them and inhibiting their ability to obtain water and nutrients.

A degree of compaction is tolerable to the soil and roots. The soil can recover from compaction if the abuse causing it is sporadic. If a tree receives a lot of abuse in the summer (for example, if it is a daily gathering place for groups) and none in the winter, during the winter months, frosting or freeze and thaw or the effects of rainwater can rehabilitate a certain amount of compaction. Only natural processes such as these and time can mitigate the effects of compaction. Unmitigated compaction around a tree’s roots will, at the very least, cause an unhealthy tree.

Suffocation

Root suffocation occurs when the surface of the soil is covered with pavement, plastic for landscaping, or excess water. It has the same outcome as compaction, but without a regular recovery process. Root suffocation can cause a tree’s death. A small amount of suffocation, such as a narrow sidewalk, is tolerable, but when half or more of the surface over a tree’s roots is covered, it negatively affects the tree.

Root Disease

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Fig. 17A“Root Rot”

(Above) Stump showing advanced stages of root rot. The red area indicates pre-decay stain. By the time the stain has reached this level, the roots have lost more than half their strength. Additional defects such as heart rot, in the center, increase the potential for failure.

(Below) Tree failure due to root rot.

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Fig. 17B

Root disease is one of the most dangerous defects a tree can experience. A tree’s root system is its anchor. If it is deteriorated by infection, the likelihood of the tree failing greatly increases.

Trees contract diseases when their roots grow into an infected area of the soil or into the roots of an infected tree. This is, of course, assuming that they are susceptible to the particular pathogen causing the disease. Disease generally enters the root system through the tip of the roots, and moves inward towards the bole, traveling along the roots. Pathogenic spores entering through a wound are yet another source of infection. In this case, the disease enters and spreads from the point of infection.

Diseases can spread from tree to tree through root grafting, a process in which two or more trees’ roots

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grow together and the root system is shared by all the trees. Root grafting only occurs among trees of the same species and only in species which are genetically predisposed to grafting. Trees that do not genetically root graft generally do not spread disease from tree to tree as efficiently. However, if the disease is present in the soil or in another tree’s roots, there is always the chance that another tree’s roots will grow into the infected area, contracting the disease.

Diseases that spread from one tree to another are particularly dangerous because they can cause several trees to fail together during the same storm or event. Among species of trees whose roots graft, root disease is more devastating because pathogens have an easier path for spreading the infection to other trees. Diseases affecting trees’ roots have the most effective system of causing a tree to be less than safe. They occur hidden in the soil, invisible to us; they affect the most important part of a tree with regard to safety; and they compromise the ability of a tree to stave off challenges from a storm. Root disease is also dangerous because it often spreads to the bole. Diseases contracted above the ground, on the other hand, seldom spread to the roots.

Once a tree’s roots have been deteriorated by disease, it becomes more vulnerable to wind. Extensive deterioration leaves the tree dependent on perfect balance to stay vertical. Of all the hazards caused by illness, a tree suffering from root infection is the most hazardous. It is possible for a tree to survive and maintain a healthy appearance, even with the majority of its roots decayed, if a small percentage (even just one or

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two) can supply the tree with sufficient water and nutrients. There usually is not enough energy to promote growth, just enough to stay alive for a while. The tree can appear sturdy while being very vulnerable to failure from wind.

Trees dying from bole or crown failure usually have obvious defects. The trees lose their “sail,” but their root systems may remain intact for several years, sometimes keeping them safe from wind failure for several years after their death. In contrast, trees dying from root decay are highly susceptible to wind failure, sometimes for several years before they die. In such cases, the tree retains a full “sail” while the roots are weaker than needed. If root decay is extensive, the tree can fail in a non-storm event. The more the root system has been destroyed by disease (or by any other means for that matter) the less force required to cause failure.

Disease Detection and Treatment

In advanced cases root disease is visible through its effect on the tree’s crown. A full, dark green crown becomes thin and yellowing. With a root system incapable of supplying an adequate amount of water and nutrients, the crown first cuts back its functions by dropping needles and then starts to die. This stressed look in the crown is often the first sign we see. In many cases, by the time a tree starts to look stressed, it is already prone to failure. When only one or a few of its roots are infected, the others can supply enough water and nutrients to keep the foliage looking healthy. When enough of its roots are damaged to the point that the

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crown no longer has enough nutrition to function properly, the tree looks unhealthy and is at risk.

There are many reasons why trees may look stressed and then die. Pollution, excess or deficient water or light, and temperature extremes are just a few. These reasons are usually attributable to some event such as a drought. If a group of trees die, and an event such as an extreme winter is not related, then disease should be suspected. The most common biological reason for a group of trees to die together is root disease. If, within a stand of healthy trees, there is one or more dead trees, along with several less than healthy-looking trees, root disease is very likely the cause.

When trees die, it is important to look beyond the individual tree. Root disease should be addressed as a tree community problem requiring evaluation and treatment of the entire community. In some cases, only selected trees indicate root disease. But if a tree is suspected of having root disease, its nearest neighbors should also be suspect.

The treatment for root disease usually involves removing the infected trees and isolating that area of the soil containing the fungi. An important thing to remember is that most root-decaying fungi only travel through live root fibers. Dead roots, then, are a barrier to the disease. If an uninfected tree is cut down, an approaching fungi will not find a medium it can continue to spread through. To stop the spread of root disease in trees that root graft usually requires removing the diseased trees and at least one healthy tree around

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the infected area. The hope is that the roots of the cut, healthy tree will die before the disease can spread through them.

The reason for removing the diseased trees is safety. If the goal is to treat a root infection area and safety is not an immediate issue, then simply cutting a perimeter of one healthy tree around the infected area can stop the spread of the disease most of the time. If safety is not an issue, dead trees can be left standing because they will provide valuable habitat for wildlife. Removing the stumps and as many infected roots as possible will decrease the amount of inoculums in the soil. If replacing the trees removed is desirable, then a species not susceptible to the given disease is recommended. Planting non-susceptible trees can result in healthy trees where a disease is present in the soil.

Root Strength

Roots provide trees with the support necessary to keep them from failing. Each species of tree has a different level of fiber strength, but that strength is always sufficient for that particular species. If at an early stage in its life, a tree regularly receives weather that challenges its roots, the roots will develop extra strength in order to prepare the tree for those challenges later on. Compromise of a tree’s roots by severing, suffocation, or disease is an adverse situation that the roots must overcome or the tree is a less than normal tree. Root fiber strength does not change with time unless they have been compromised.

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Damage to roots can create an open wound which invites infection by soil or waterborne pathogenic spores. Not only does root damage interfere with a tree’s structural stability, but it also predisposes the tree to outside forces that may begin an infection whose impact will only increase over time. If it becomes necessary to damage a tree for more important functions, then the damaged tree should be carefully monitored. If a tree is damaged or deteriorates in such a way that it presents a threat, then it should be managed as a high-risk tree.

Soil

Soils are a critical issue in terms of tree failure. Not only does the soil affect a tree’s health by supplying it with nutrients and water, it is the material that the tree grabs onto when it is threatened by a storm or by other forces. Soil differs in its composition and characteristics from place to place. Each soil develops a unique relationship with the trees it supports. Each soil has a unique profile ranging from deep, sandy soil where trees can send their roots to unrestricted depths to shallow, rocky soils where trees struggle to find a place to anchor themselves or to find water and nutrients.

When the soil is favorable to root penetration, the roots grow vertically deep where they can find water when there is drought at the surface. Deeply penetrated roots can find much to anchor to during a storm. When the soil is shallow, there is not much vertical root penetration. The tree sends its roots down until they meet resistance and then grows them in a horizontal

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direction just under the surface where they ordinarily run into other trees’ roots or other obstacles. The restriction may be bedrock or certain soils, such as hardpan and clay pan, that are compacted and restrict root movement. Trees growing in such circumstances are more easily affected by weather conditions such as drought. They also don’t have much to anchor to when challenged by a storm.

Water significantly affects the soils’ ability to support the roots in their role of holding the tree up. The same water that is essential to tree growth can negatively impact the tree’s stability by weakening the soil’s root-holding capability. When the water supply in the soil is low, the soil shrinks; soil particles draw closer together resulting in the strongest level of root-holding strength that the soil is capable of. As the water supply increases, the soil loses its cohesive strength and becomes plastic, and eventually can become viscous in which case it has very little root holding capability. It is during this stage of soil/water relationship that trees are most vulnerable to storm damage. In this case, even the most stable and healthiest of trees can fail because the soil around its roots is weak. The tree essentially uses a non-supporting medium for its support.

Roots are the hidden parts of a tree. To a functioning tree, the roots are just important as the visible segments. The roots support the foliage by providing them with nutrients and water, and the foliage does the same for the roots. Yet we seldom consider or discuss the role that they play in the trees we admire or use. We may have great admiration for nice trees in our yards, parks,

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or camps without thinking about the roots that support them. We trample around them, compacting the soil, and suffocating the roots. We cut them to build roads, trails, driveways, and even septic systems. We clear away brush and shrubs, allowing direct sunlight to strike the ground, warming the soil whereas the roots prefer the soil cool.

It is not necessary to be overly concerned with the roots’ daily functions as long as we do not impair them. Care should be taken to avoid compacting the soil around the roots, exposing the soil surface above them to direct sunlight if they are not used to it, and they should not be cut if doing so can be avoided. We should remember that abuse of the area and soil around the tree will result in malfunctioning roots which will eventually be reflected in the health and appearance of the foliage that we do enjoy.

A certain amount of development is desirable and even required by people for homes, parks, camps, and campgrounds. The important concept to keep in mind is that if we are to significantly damage a tree’s roots, bole, or crown, we have created a hazard tree situation for future owners or managers to contend with. If we damage a tree as such, we should remove it and replace it with a desirable healthy tree which will not threaten anyone or any structure in the future.

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CHAPTER FOURWeather Factors

Wind challenges a tree’s ability to remain vertical more than any other weather factor. Trees develop resistance or strength to receive that challenge, as well as for ice and snow.

Wind

Appendix

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Fig. A“Reference Tree”

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Fig. B“Wind Stress”

Wind stress (indicated by blue arrows) onto a tree.

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Wind is the primary cause of tree failure. It is the force that challenges a tree and attempts to push it beyond its ability to remain vertical. Other factors such as disease or weak roots may reduce the tree’s ability to resist the force of the wind, but wind is usually the ultimate force that causes failure. Mild winds, if gusty, can lead to tree failure by causing swaying. Tall, slender trees can sway in a mild wind until they reach a threshold, then they fail. The bole may snap off or the roots and/or soil may reach a point where the tree is overcome either by sheer power or through shaking.

Unlike most winds, gusty winds offer a unique challenge to trees. Trees can buttress as a long-term defense against sustained winds but have no real defensive strategies against gusty winds. They become dependent on the soil which plays an equally important role in defense against wind, especially when the wind is gusty. Gusty winds tend to shake a tree back and forth, causing the holding capability between soil and roots to weaken. In this case, the gusts weaken a tree, portions of a tree, or the soil around the tree, and then a period of sustained wind completes the failure.

The failure from sheer wind power has a predictable direction of failure with the wind. The failure from shaking has an unpredictable direction of failure. The tree simply shakes back and forth or in a random fashion until it fails from its own momentum. It can fall in any direction.

Wind Velocity

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The velocity of the wind has a direct relationship to tree failure; the stronger the wind the greater the probability of failure. It is the combination of wind velocity and the amount of wind that the tree captures that determines the amount of resistance needed by the tree to remain vertical or to keep its parts intact. Wind has more effect on weak or sick trees, but as velocity increases, its effect on the stronger, healthier trees also increases. The first effect is on small branches, then on larger branches, and then there is a threat to the entire tree. A rule of thumb for foresters has been to leave the woods when small branches begin to fall; it is realized that any additional intensity in the wind will increase the amount of failed trees, and consequently increase danger.

Winds with high velocity can cause failure in perfectly healthy trees. Strong winds challenge a tree with a certain amount of force and then simply overcome the tree by applying more force than the tree, the roots, or the soil can withstand.

Wind Pattern

We have no control over the wind or how it blows – strong, gusty, sustained, or harmonic. However, we can manipulate, sometimes inadvertently, its direction and effect, with structures, for example.

Trees adjust to what the wind does. If wind prevailingly blows from the east, then those trees exposed to wind build defenses for east winds.

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The pattern of the wind has a different relationship with the various structural designs or shapes of trees, and with different parts of trees.

There are 2 basic wind patterns that affect trees:1. The steady, sustaining wind2. The gusty, erratic or harmonic wind

The steady wind is simply force against resistance. The wind challenges the tree, and the tree resists that challenge. If the force of the wind is greater than the tree’s ability to withstand it, all or part of the tree will fail.

The more flexible or plastic species, such as the cedar or willow, may be able to use their bending capabilities to withstand and survive a sustaining wind, but those same qualities may cause the tree to be more susceptible to a gusty wind. Such winds cause the more flexible trees to whip or sway back and forth until the momentum causes failure. Ordinarily, flexible trees tend to succumb to breaking at the bole more than uprooting during gusts.

The less flexible species, such as the Douglas fir, tend to uproot more often than break off. Their strength keeps the crown from swaying back and forth, causing bole or limb failure. Their resistance to bending with the wind causes them to capture more wind, exerting excess stress on the lower bole, root system and the soil as the stress is transferred down the tree.

Each portion of the tree absorbs what stress it can and passes the balance on to another part, from small

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branches to large branches to upper bole to lower bole to large roots to fine roots to soil. At any point along this line of energy transfer, failure can occur. Failure at any point along this continuum relieves stress for the succeeding portions of the tree.

Manipulating a tree can control the amount of stress exerted onto the tree by reducing the amount of wind the tree captures (See discussion of pruning and topping on page 74).

Wind Channeling

In areas where the space available to the wind narrows, channeling occurs. Wind can change direction to follow a channel between hills, between buildings, and along tree-lined streets and roads. Wind packs more energy if it has to funnel from a large area to a small area. This is particularly important in developed areas; structures can have the same effect as topography. Architectural designs, landscaping, and layout can create channeling with trees associated with a given project as well as trees not associated with the project. The trees not associated with but near a development will be affected by any change in wind or wind channeling created by the project development.

If residual trees are saved from the original stand and are not carefully selected for structural soundness, a hazardous tree situation is created - weak trees experiencing winds from directions and in strengths they are not prepared for.

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Because healthier trees generally produce higher quality forest products, they are the trees selected for harvest and deliver to the mill during the logging phase of developments. The trees retained for landscaping are generally picturesque trees. The aspects that make them picturesque are the same aspects that generally make them a poor selection for forest products: defects and disease. This can also make them a poor selection for retention, particularly if people will use the area. Trees that are to be saved for retention around new structures should be evaluated and selected before a timber harvest or clearing. The treatment of the area around trees selected for retention is as important as the selection of the trees themselves. The effects of the structure on the wind, especially prevailing winds, should also be a consideration.

Lee Winds

On the lee side of hills or structures, winds tend to be more erratic and unpredictable. When wind encounters an obstruction such as a mountain, hill, trees, or structure, it will blow over and around that obstruction. When the winds join again on the lee side of that obstruction, erratic and turbulent patterns develop. While the direction of tree failure is usually predictable in a sustained wind, the direction of tree failure is often unpredictable on the lee side of obstructions. Forest stands on the lee side of hills, experiencing wind failure, usually fail in a “jackstrawed” pattern; trees fall in all directions. Particular importance should be placed on the selection of trees where lee winds will occur.

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Shorter healthier trees should be selected over taller defective trees.

Wind Duration

A persistent windstorm is effective in causing tree failure due to the continued disturbance. If a wind begins to shake a tree back and forth, or exert stress over a long period of time onto the tree, it will weaken the bond between the roots and soil. It will also affect the fibers in the limbs and bole. As the duration of the storm extends, the probability of failure increases, creating an irreversible process. The duration of one storm is more detrimental than two storms of the same duration. In a single sustained storm, the tree does not have the opportunity to recover or to stabilize itself from damage sustained to itself or the soil around it. With two or more storms, there is recovery time in between. The most significant factor is that some water will have drained from the soil, allowing the root-holding capacity of the soil to begin to return to normal before the next storm.

The soil can become loose and viscous from saturation during a storm event. After the event the soil immediately begins to return to its normal level of cohesion. The bond between the soil and the roots begins to reestablish itself. If sufficient time passes, the roots/soil bond returns to normal. If insufficient time has passed between storms, the tree will enter the new storm in a weakened state.

The Edge Effect

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Fig. 2A“Edge Effect”

(Above) This narrow strip, left over from a previously dense forest, is now exposed to weather the trees are not prepared for.

(Below) A closer look at the same trees shows that when exposed to storms, the failure potential is higher than normal.

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Fig. 2B

Trees at the edge of a forest develop certain characteristics because they experience and adjust to the brunt of the weather. They also protect the trees in the interior. Trees in the interior of a stand do not experience the same winds and, therefore, do not develop the defense mechanisms of the trees on the edge. In a stand where the tree density is high and trees are spaced close together, the trees literally hold each other up. Trees at the edge of a stand will grow large limbs toward the opening because they receive more light from that direction. They also develop extra strength for wind firmness. This results in some of the trees being weighted toward the opening, and away from the stand of trees. This process takes place over long enough periods of time so that the edge trees are

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conditioned to the climatic extremes that they will probably encounter over time.

Tree failure from wind increases drastically along the edges of clearing boundaries. This failure potential stretches over one or two tree lengths in from the new forest edge. The important thing to realize here is that a forest or a group of trees adjusts and stabilizes to encounter those elements that they are ordinarily exposed to, and each tree has a specific role to play in the group’s encounter with the weather. Any interference with this stability causes a change in how the forest or the group of trees reacts to weather; the probability of tree failure increases.

The dilemma is that trees are a desirable attribute of places humans frequent, but the trees are not selective about when and where they fail. The situation is manageable; we can have safe, aesthetically pleasing trees in the places that we frequent.

Developments change the way wind behaves in a local area. Knowledge of wind history is critical in planning which trees can be left standing. If historical wind activity has been damaging trees, it can be interpreted from the trees’ appearance. Even with callused-over wounds from past wind activity, telltale signs in the trees’ structure can be used to identify past weather patterns. If limbs are short on the east side of a tree and long on the west side, we can guess that strong prevailing winds approach from the east.

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When planning for the trees to be retained, consideration should be given not only to wind history, but also soil, drainage, topography, rainfall, the structure of the pre-existing stand and the health and physical condition of the trees to be retained. Consideration should also be given to the treatment of the residual trees. For example, clearing the brush from around a tree may increase solar heat to the soil, increasing its temperature and causing the soil to desiccate, slowly killing a tree that was previously comfortable with a cool, moist soil. Care should be taken when transplanting trees from one area to another. If trees are moved from an area that historically does not experience strong wind to an area that experiences strong wind on a regular basis, those trees are more likely to fail.

These concepts are particularly important in housing developments where trees previously existing in the interior of a forest are left standing and structures are constructed among them. This results in weaker trees weighted to one side exposed to strong winds. Narrow strips of trees left between homes in newly developed areas have a very high potential for failure, and because of their proximity to homes or structures have a high probability of doing harm to humans.

Rain, Snow, and Ice

Rain, snow, and ice have three effects on trees: they add weight, they increase the sail effect, and they saturate the soil. When a tree starts to lean, its center of gravity moves from directly over the center of the root system to

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another point over the ground, the exact location of which depends on the severity of the lean. Additional root strength is needed to keep a leaning tree from failing. Any added weight, such as from rainwater, snow, or ice, creates gravitational forces that contribute to pulling the tree down. Previously saturated soil further adds to the probability of failure as extra weight is being added to a less than desirable anchoring system.

Dead and weak branches are vulnerable to the added weight of rainwater, snow, and ice. If the branches are covered in moss, their water-holding capacity is higher still, consequently increasing the weight of the branch. Most dead branch failure occurs during or soon after snowfall or ice buildup. Dead branches have unpredictable and decreasing strength, consequently any amount of added weight can cause failure. Even though most dead branch failures occur during a storm event, in some cases the storm may weaken the branch enough so that its potential for failure is high during calm weather.

Healthy branches can fail from snow or ice buildup, but generally not from rainwater. Branch failure from snow or ice generally occurs on the mid to lower branches of the tree crown. The upper, younger branches are more plastic, but the rigid lower branches succumb to the weight, furthermore they experience the total weight of the build-up further up in the crown. The dangerous effects of branches are usually in the immediate vicinity of the tree, as they usually fall straight down. However, in strong winds, branches can be carried for some distance, depending on the velocity of the wind and the sail of the crown. The hazard from snow and ice to a

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leaning tree is generally the height or striking distance of the tree.

The plasticity of the upper crown can be the tree’s own enemy during snow and ice buildup. If the main stem bends, the center of gravity shifts, and the weight of snow or ice becomes more effective in causing breakage. The dynamics of the storm have changed; the weight is no longer pushing the tree down. The bent bole is now receiving sheer stress, causing breakage. The plasticity of the upper crown is good defense against wind, but it is a detriment in defending against snow or ice.

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CHAPTER FIVEIndicators

(Signs and Symptoms of Defects)

Ants

The presence of ants on or around a tree indicates a possible cavity. In some cases, ants excavate their own cavity, and in other cases they occupy cavities created by other insects, pathogens or mechanical injuries. Excavation by insects can generally be diagnosed by the presence of a fine sawdust, called frass, on or around the tree. The ants’ source should be located. A nest located inside the bole or roots indicates a cavity inside the tree which should be treated (see Cavity on page 46).

Broken Branches

Broken branches are a normal part of a tree’s existence and are not usually a cause for concern. Most trees have a broken branch or two. Broken branches indicate that the tree received more stress than it was prepared for,

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most likely from excessive wind, snow, or ice, or a combination of these. Branches that are broken some distance from the bole do not indicate any defect and do not threaten the tree. However, branches that break off at the bole or break along with a piece of the bole indicate weakness in that area of the bole. These breaks can result from normal tree/weather encounters or from a weak tree failing under minor weather conditions. Interference with the tree or its surroundings can also cause a tree to receive weather it is not prepared for so that ordinary weather has greater effect. In such cases, the tree should be managed as a high-risk tree, at least until it has adjusted to its new environment.

Infected Knot

Decayed Wood

Healthy Branch

Fig. 15

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“Pathogenic Access”One venue for pathogenic access is through broken or pruned branches.

Cavity

A cavity is a hole in the bole or on a limb that generally results from decay inside the tree. Broken branches or wounds expose the tree’s fibers to infection by pathogens. When a tree gets infected, a contest begins between the tree’s ability to callus over or outgrow the infection and the pathogen’s ability to infect new fiber. Wherever the tree loses part of that contest, a cavity develops. The cavity may be filled with rotted fiber, it may even provide a home for insects or small animals, or it may be void.

Cavities detract from the tree’s ability to remain structurally sound. However, the tree may try to counteract the cavity by growing stronger fibers around it. These new fibers are matted in a pattern that provides as much strength as possible from the limited amount of fiber. These matted fibers may also resist infection because they are usually harder than normal fibers and in some cases impregnated with pitch.

The investigation into a cavity should include a search for conks, or other mushroom-like growth, on or around the tree as this may indicate the presence of a pathogen.

Color Change

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The unseasonal changing of the color of foliage may indicate an illness in a tree. The roots may be damaged or diseased to a point where they no longer supply sufficient nutrients to the foliage. The bole or branches could be damaged so that water and nutrients cannot pass through, or the needle and/or leaf change could be caused by needle blight. Quite often a tree can recover from a condition effecting color change. It is imperative that the agent affecting the tree’s foliage is diagnosed so that the situation can be monitored.

Certain species such as western red cedar occasionally fluctuate in crown density and color. This should not be confused with a sick or dying tree. Knowledge of the behavior of the species being evaluated is just as important as the knowledge of defects themselves.

Conks

Conks are the fruiting bodies of pathogens that attack the structural integrity of a tree. They may appear on the bole, on branches, on root collars, or on the ground near the tree. Each disease displays a unique conk. Some pathogens present their conks in the early stages of development, and some present theirs in the latter stages.

Any mushroom-like growth on or immediately around a tree’s bole should be analyzed. The presence of a conk is an indication of disease attacking the tree somewhere in its structure. The disease should be identified and its effect on the tree’s structure examined. In most cases serious consideration should be given to the infected

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tree’s removal, modification, or at the very least, avoidance during storms, because conks indicate that the tree’s structural integrity has been compromised.

Crooks

Normal branch

Spike knot

Spike branch

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Fig. 18

“Crook”Crook and associated indicators

Crooks are shifts in the lineal alignment of a tree’s bole; they are a tree’s adjustment to a past break. If the bole is cut or broken, generally a lateral branch takes over as leader and begins to grow vertically. Over time the wound calluses over, but the new bole (the now vertical limb) is not centered over the previously existing bole. Crooks are significant because the tree’s fibers were exposed to pathogens during that time when the tree’s bole was cut or broken and any pathogenic infection that occurs becomes internalized into the tree. If the break that resulted in the crook was infected and then callused over during that time when the fibers were exposed, there is a great potential for hazard. The portion above the crook is gaining weight through growth while being supported by an infected bole growing weaker from decay.

Damaged Roots

Root damage can be caused by natural occurrences such as landslides or erosion. However, most root damage is caused by mechanical means through land clearing, road and driveway construction, utilities installation, and landscaping. Pathogenic infection does not generally result from damaging a small layer of bark; in most

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cases the bark will re-grow and close over the wound. If the fibers are broken, exposing the wood itself, fungal spores may infect the tree. Exposed wood fiber is the most common method of pathogenic invasion. Damage that is extensive enough to result in broken roots not only exposes the tree to pathogenic invasion, it also interferes with the natural structural design of the tree. This disrupts the balance of the roots’ design and soil-holding capacity, and consequently the tree’s defense against wind.

Dead Branches

Most mature trees naturally have a few dead branches. If a branch dies and remains attached to the tree, it is only a question of time before it falls. Ordinarily dead branches break during a storm or with the added weight of rainwater, snow, or ice. They can and do break even on calm days and may fall at the most inopportune times, such as when someone is present below. Continuous decay and changes in moisture content due to weather affect the balance and strength of the branches, deteriorating them until they fall. Dead branches located above places where people commonly gather or travel should be removed, or another gathering place should be selected.

Even though dead branches are the results of a tree’s natural function, a significant number of such branches may indicate disease, insect attack, or weather-related damage, and further investigation may be appropriate.

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Dead Top

When the upper portions of a tree’s crown die, the cause may be small animals such as porcupines chewing off the bark, low water supply in the soil causing drought, the tree’s inability to get water supplied to its upper crown, or previous damage from a pathogen infecting a wound in the tree. The tree may callus over the wound with the infection inside. The pathogen can continue to negatively affect the tree’s functions so as to cut off circulation at that point on the tree, causing the portion above the wound to die sooner or later.

Dead Tree

Fig. 20A

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“Dead Tree Failure”Dead trees deteriorate until they fail as in bole failure (above), or root failure (below).

Fig. 20B

Fig. 21A

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“Root Decay”Trees failing without root and soil mass indicate root disease. Consequently, the neighboring trees should be suspect.

Fig. 21B

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Fig. 22

“Hazardous Tree Failure”Decayed roots from disease can result in damage to human concerns..

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Fig. 23B

Dead trees, also called snags, are inherently unstable. That is why they are considered a level one hazard. The level and type of instability depend on when and why the tree died. If it died from root decay, it has lost its anchoring system and will likely fall over sooner or later. Anything within striking distance is at immediate risk. Any tree with a failed root system is a high-risk tree. If a tree dies from an above-ground problem, then it decays from above the ground first, and the main threat, at least for a while, is the area underneath the tree itself. The danger from decayed branches or the upper crown falling is high. Once a tree dies it continues to deteriorate until it fails. Dead trees make wonderful wildlife habitat, but they are unstable. Even though trees that die from above-ground problems are more stable than trees that die from root failure, their roots are continuing to decay. It is only a question of time before their soil-holding capacity decreases to pose as much threat as those trees that have died from root decay.

If dead trees are to be kept for wildlife or aesthetic purposes, they and the area around them should be avoided, especially during storms. If the area around dead trees cannot be avoided, the tree should be removed.

The cause of death for any tree should be determined because it may indicate the impending death of

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surrounding trees. Certain insects attack and kill a single tree and stop there, but in some cases the single dead tree serves as the starting point of an infestation of insects or pathogens that has the potential to keep spreading. Any investigation into the death or illness of a single tree should include the neighboring trees.

Disease Pocket

A disease pocket is a group of trees that includes several less than healthy trees. Some are dead, some are dying, and some are just starting to show signs of illness. In most cases the cause of a disease pocket is pathogenic activity spreading from tree to tree. Laminated root rot, for example, spreads from tree to tree by way of root grafting or root contact.

Insects attacking a group of trees can have the same effects. The insects can attack a single tree, build up their population and then spread out from there, or the expanded numbers can attack as a group. Different insect species attack different portions of a tree; some attack the foliage, some attack the woody portions, and some attack the bark.

Excessive Cones

When a tree produces an unusually large amount of smaller-than-normal cones, it may be a “near death” response. Trees under stress sometimes put their final supply of energy into reproduction rather than growth. This should not be confused with a good cone year. Cone-bearing trees have good and lean years with

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respect to cone production. However, a tree that appears to have an excessive amount of smaller-than-normal cones should be checked for additional signs of illness.

Exposure

Exposure refers to the relative force and direction of wind that a tree or group of trees is likely to encounter. Exposure analysis can predict the relative risk and safety of nearby human concerns. For example, if a tree is regularly exposed to strong north winds, it should be realized that human concerns on the south side of that tree have a higher than normal risk.

Fire Scar

Forest fires, slash burns, and campfires all can have significant effects on trees provided that they get close enough. From barely heating the bark to totally burning portions of a tree’s bole, fires damage trees. Fire scar is the aftermath of a tree’s encounter with fire. As with any other wound, as soon as the encounter is over the tree begins to callus over the wound. Most fire scars are visible by a charcoal layer on a tree’s bole, and the perimeter is surrounded by new tree growth which the tree has added in an attempt to cover the wound.

The scar may occur along the base of a tree, such as it would if it were caused from a campfire burning too closely. A forest fire scar may be farther up a tree’s bole. The fire damage could have occurred a hundred years ago and be at least partially callused over. If it is totally callused over then the situation is hidden, as a

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seam is the only indication that there was damage to the tree. The charcoal offers some protection to the tree from airborne pathogens, but the drying of the wood fibers by the fire also opens cracks in the charcoal and the tree which functions as a venue for pathogenic invasion.

Any damage to a tree that results in exposed fibers has the potential for fungal infection. Quite often there is decay inside the charred layer of a fire scar. Checking for the extent of defect inside the scar is therefore prudent.

Flagging

When a small portion of a tree’s foliage turns colors, generally reds and browns, it is known as flagging. Different species have different reasons for flagging, and different biological enemies such as insects have varied effects on foliage. Some trees such as western red cedar have flagging periodically as a normal process of replacing old foliage with new. Some pines and firs show flagging as a result of rusts or insect attacks on the foliage. Dry winds can burn the needles or leaves of some trees. Fungal activity such as needle cast can kill portions of a tree's foliage, also causing flagging to occur. Flagging in itself is not sufficient reason to condemn a tree, but it is sufficient reason to look for further signs of weakness and monitor the tree’s condition.

Flat Crowns

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Flat crowns are an indicator of problems in conifers. Conifers generally have a sharp crown pointing upwards. When a conifer begins to look like a hardwood tree with a rounded crown, this is flat crown. Tree crowns flatten due to old age, poor health, or damage. Crown flattening in a young tree is possibly due to ill health; damage or disease in the root system is likely. If a tree does not have sufficient energy to continue to grow at a normal rate, it will place its energy into maintenance. The tree stays alive but new growth is minimal in the leader, resulting in a flat crown.

Frass

Frass is produced by insects chewing and excavating the bark or woody tree fibers. It is a sawdust-like material deposited on the bole or at the base of a tree. The color of the sawdust sometimes indicates what part of the tree is being excavated. For example, dark brown frass indicates excavation in bark, and white or light brown frass indicates excavation in wood fibers. This produces no imminent danger of tree failure, but the tree should be checked occasionally to see if the insect attack has any effect on it. Insects ordinarily invade trees. They like to excavate holes in the bark and lay their eggs; the inner bark also provides food for larvae. One or two insects are probably no cause for concern. But a dozen or more invading the same tree may be a problem, especially if that tree has other problems or defects.

A large hole producing frass indicates a cavity supporting an insect’s nest that has affected the tree’s structure. This may be cause for the removal of the tree,

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or at least for further investigation. Monitoring should also take place because some insects can and do sense weak, sick, or stressed trees and attack them. The weakness or stress may be the result of drought or decay.

Frost Cracks

Fig. 14 “Frost Crack”

Frost cracks indicate decay inside the tree.

Frost cracks are indicated by a vertical seam on the surface of the bark of a tree. This seam can range in length from only a few feet to almost the length of the tree. There are three theories explaining the cause of frost cracks: 1) A tree which is wounded in its juvenile stage gets

infected, is callused over, and this contracted decay expands as the tree grows;

2) An early winter causes a tree to freeze before it hardens off for the winter, causing the tree to crack;

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3) Decayed wood inside the tree normally holds more water than normal fibers. During freezing weather when this water freezes and expands, it forces the bark to stretch and crack.

More important than knowing the exact cause of the crack is realizing that frost cracks indicate decay inside the tree’s bole.

Girdling

Girdling involves the choking-off of a tree’s function around the bole or limb. Girdling is usually a result of mechanical damage. If a fence, for example, is wrapped around a tree’s bole, it restricts the tree’s ability to expand or to move hormones, water, and nutrients up and down. As the tree continues to grow, the fibers pack tighter until the movement of water, nutrients, and hormones is blocked. Continued pressure can kill the tree.

Girdling from natural functions such as ivy seldom occurs, although ivy may become a part of several factors that kill a tree. Vines are generally not a girdling threat; their threat is more from shading if their growth engulfs the tree’s crown and robs them of sunlight.

Hanging Branches

Known as widowmakers, hanging branches are ones that are partially broken, and held in the tree by some un-severed fibers or other branches. Hanging branches may also be completely severed but suspended, balanced in

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the crown. They usually require a wind to dislodge them, but they do have the potential to fall at any time.

Heavy Branches

Heavy branches are those that have more foliage and/or size than normal. Parasitic plants such as dwarf mistletoe generally cause this excessive growth, but trees growing in the open receiving unrestricted water, sunlight, and nutrients can also develop this trait. The potential for these branches to break off is higher than normal, as they carry excessive weight and have a large sail. Additionally, they catch and hold more snow, ice, and wind. increasing the chance of failure, especially during storms.

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Fig. 1

“Widowmaker”

A broken branch suspended in a tree is a level 1 hazard because it can fall during ordinary weather.

Hidden Defects

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Hidden defects are those defects inside a tree that on the surface offer no obvious signs of their presence. Generally these defects entered a tree through small, inconspicuous places or started affecting the tree at an early stage. Surface recovery is so complete that they are very difficult to detect. Sometimes a tree can be completely hollow and yet give no visible signs.

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Hole

Fig. 23A

“Hole”(Above) Hole indicates decay inside tree

(Below) Cut exposes decayed wood.

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Fig. 23C

“Hole”Plan view of stump shows more decay.

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The aspects that make trees interesting subjects also make them a hazard risk. A tree supported by decayed roots is a hazard.

Fig. 23D

Cross section of root system shows increasing decay.

Fig. 24A

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Fig. 24B Fig. 24C“Fungi”Fungi are signs of tree failure. Any fungi growing on a tree indicates decay inside the tree

Mechanical damage, disease, insects, animals, and birds create holes in trees. Some holes indicate severe defects inside the tree, and some are superficial. A hole indicates a breakdown in the interior structure of a tree. If there is a cavity inside the tree, the visible part will ordinarily show the smallest diameter. All cavities are at some stage of being callused over by new growth. Trees will continue to add fiber around the perimeter in an attempt to callus over the wound completely.

Holes created by woodpeckers and other wildlife indicate deteriorated wood in the bole providing habitat for insects, which are attracting birds in their search for food. Small holes in a horizontal arrangement ordinarily do not create a hazard; this is probably a function of

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sapsuckers who do not damage the tree significantly but do expose it to fungi.

Fig. 8A“Hole”

Hole in a tree’s bole indicates defective wood as shown in the cross-section below.

(Below) Green arrow indicates sound wood.Blue arrow indicates decayed wood.Red arrow indicates pre-decay stain.

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Fig. 8B

Fig. 9A“Holes”

(Above) Small holes indicate insect activity.

(Below) Large holes indicate pathogenic activity.

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Fig. 9B

Fig. 10A“Holes”

(Above) Insects (ants, beetles, etc.) can occupy cavities created by pathogens.

(Below) Insects can excavate their own cavity.

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Fig. 10B

Leaning Tree

Trees lean for any number of reasons: shifting soil, storm damage, response towards light, failed roots, mechanical damage, and any combination of these. A tree’s normal position is vertical. The roots, bole, and crown are designed for a certain level of balance, using gravity as a positive force. When a tree begins to lean, the effect of gravity is negative, putting stress on the root systems constantly.

If a tree growing alongside a high-use road is leaning over the road, it is probably a level one hazard. If it is leaning away from the road into the forest, it is probably not a hazard. The only advantage of a leaning tree is that the direction of failure is usually predictable.

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Lightning Scar

This type of scar usually appears as a spiral seam around the bole of a tree, or it may be a long straight seam along the bole. Sometimes lightning scars are hard to differentiate from frost cracks, and the only distinguishing appearance is that the lightning scar ordinarily travels in a spiral design the full length of the tree, sometimes showing up in neighboring trees as the lightning bounces around from tree to tree.

If the damage from lightning exposes raw wood fibers for any length of time, there is a possibility of pathogens infecting the tree. While a lightning scar does not in itself indicate a hazardous tree, the probability that the tree is defective is greater than normal. If the tree is large and exists near an area frequented by humans, it should be managed as a high-risk tree, unless further study shows that the tree is structurally sound and not a threat. When investigating lightning damage the surrounding trees should also be checked.

Loose Bark

Loose bark results from damage to that area of a tree’s bole between the bark and wood. Fire can heat the bark up to a point where it is not charred but cells have died. Another tree can fall, striking the subject tree and killing cells at the inner bark. If the inner bark cannot function and the outer bark is still attached, trees simply grow

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new bark under the non-functioning bark, sloughing it off.

Certain species normally slough off loose bark to provide for the expansion of new growth. An excessive amount of loose bark with these types of trees can indicate possible damage. For those trees that do not normally produce loose bark, it is an indicator of damage to the area between the inner bark and the woody portions of the tree. Sun-scald can also result in loose bark. If trees that have been growing in a shaded environment are suddenly exposed to direct sunlight, the exposed bark could be scalded from solar radiation. In these cases the new undamaged bark grows and expands underneath the damaged bark, causing it to slough off. In most cases, loose bark does not indicate further defect because pathogens do not ordinarily have access to the tree’s fibers. Loose bark should be reason for monitoring.

Multiple Stems

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Fig. D

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Fig. 3“Multiple Stems”

Multiple stems have the same hazard development processes as a forked tree.

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Fig. 7A

Fig. 7B

“Failed Fork”

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Fig. 4“Forked Tree Failure”

The potential for failure at a fork is high due to increasing weight of the stem supported by decreasing

strength at the fork.

Decay decreases the holding strength of forked trees

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When a tree’s bole is broken, the nearest limbs begin to vie for dominance. In most cases, one of these branches wins and becomes the leader. When all the vying branches continue to grow at an equal pace, the result is multiple stems. The danger arises from the period of time between the break and the wound callusing over. During this stage, the wound is exposed to airborne pathogens, creating the possibility of infection. Failure of one or more of the stems depends on the stress created by the weight of the stem and the holding strength of that part of the tree, especially if it has been infected by pathogens. The holding strength of the tree is affected by the possible presence of decay, and the stress created by the multiple stems is affected by the weather. Rain, snow, and ice add weight, and wind adds stress.

Mushrooms

Certain mushrooms are the fruiting bodies of fungi causing decay inside a tree’s roots or bole. Some tree-decaying fungi produce fruiting bodies on limbs, the bole, or root collar, and some produce fruiting bodies on the ground near the tree. Some of the fungi most devastating to trees have a fruiting body as a brown mushroom on the ground.

Pitch

Any pitch on the outside of the bark is cause for concern. Pitch normally functions inside the tree. It is used by some species as a lubricant between rubbing fibers when there is much swaying from wind exposure.

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A small, round ("" diameter or less) hole with pitch indicates that insects have drilled a hole and the tree is producing pitch to force them out. Ordinarily a few pitch-outs occur, but a large amount suggests the tree should be monitored, along with any surrounding trees. Some beetles can determine when certain trees are weak or sick and attack those trees. Some trees, when wounded, produce pitch to cover the wound, creating a barrier against airborne pathogens. If the wound calluses over and the pitch continues to flow, the tree should be investigated for structural defects. A core sample would present valuable information.

Root Suffocation

Root suffocation is a common result of construction and landscaping. Root suffocation is the choking off of the normal air exchange between the soil around the tree and the atmosphere. Plastic sheets, bark dust, concrete for a patio, asphalt for driveways, and even excessive dirt piled up around the base of a tree are common ways of suffocating a tree’s root system. The symptoms of root suffocation are similar to the symptoms of root disease - a stressed crown.

Rust

Rust is a fungal disease that displays itself on the bark of a bole or on a limb as a pitchy, weeping sore. It is a parasitic fungus that kills the limbs or bole of the host trees by girdling the stem. Because this fungus kills the tree from above the ground, uprooting potential is low at

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first because the root systems are not affected. As deterioration progresses, the hazard potential increases.

Sail

This is the amount of wind that a tree is capable of catching. The larger the crown, the more sail and, therefore, the more effect wind will have on that tree. The amount of sail is important for two reasons: 1) It increases the failure rate, especially if a defect

such as root and stem disease is a contributing factor2) The sail can be manipulated through pruning. A

percentage of the branches can be removed to reduce the catch factor of the sail or a portion of the sail can be removed through topping. (See discussion of pruning and topping on page 74)

Trees growing in open spaces grow large sails, but they also grow sufficient limb and bole strength to support such dense, healthy growth. Trees growing in spaces with less than desirable light and water produce smaller, thinner crowns, and just enough limb and bole strength to support this level of crown or sail development.

Both crown, or sails, are well adapted to continue to function in their given environment. It is the occasional severe storm that they are generally not prepared for that causes them to fail.

Sawdust - See Frass.

Scar

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Fig. 11A

“Scars”

(Above) Scar on tree’s bole indicating defect inside.

(Below) Extensive decay found inside the scar.

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Fig. 11B

Fig. 12A“Scar”

Scar (above) indicates defect (below).

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Fig. 12B

Scars on trees will, in time, become hidden defects as the tree will sooner or later callus over the blemish. In most cases, the scar will eventually be hidden from view and that area will become a seam.

A scar that is weeping pitch or any other type of liquid is indicative of a more serious condition such as rust or an internalized defect that the tree is unable to contain.

Seam

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Fig. 13

“Seam”Seam from bending caused by heavy snow load.

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.

A seam is a wound that has been callused over by a tree. The seam is that area of the defect where callusing growth from both sides of the defect meet.

Spike Limb

A spike limb indicates possible defect inside the tree. It differentiates itself from other limbs by growing at different angles or in different patterns than the normal branches. These limbs form as the result of a wound or break in the tree’s bole. When a tree’s bole breaks off within the crown and two branches compete for dominance, the spike limb is the loser. While the winning branch takes over as the new bole, the losing limb gets distorted by the growth of the new stem. Sometimes a spike limb is the only sign that the tree’s bole was once broken. The best way to identify a spike limb is to observe the general pattern of the limb’s nodes and watch for those few that are distorted.

Split

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Fig. 16“Split”

Split tree from wind bending.

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Fig. 17A“Root Rot”

(Above) Stump showing advanced stages of root rot. The red area indicates pre-decay stain. By the time the stain has reached this level, the roots have lost more than half their strength. Additional defects such as heart rot, in the center, increase the potential for failure.

(Below) Tree failure due to root rot.

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Fig. 17B

A split is the result of incomplete tree failure; the tree bends enough to split but not to break. The bending that causes splits can be a result of severe snow or ice load as well as wind or mechanical means. Splits can occur anywhere on the tree and in most cases are not obvious, perhaps showing up as a faint line along the bole. However, splits predispose the tree to failure in upcoming storms and also expose the tree’s fiber to pathogens.

Swell

Trees appear swollen for several reasons: buttressing as protection from wind; callusing around a defect; response to light and interference, such as lean; and parasitic plants

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Swelling can often be confused with buttressing. However, buttressing should only occur at the lower bole and nodes. It is often difficult to differentiate the two, but extra fiber observed outside of these areas is a strong indicator that they are caused by swelling. Core samples expose some internalized defects. Swollen areas from parasitic plants usually occur on limbs but can occur on the bole. Swell from parasitic plants such as dwarf mistletoe is usually obvious from the distorted limb and foliar growth.

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Thin Crown

The tree’s foliage should block out most of the sky when viewed through the crown from at least 50 feet away (less for small trees). Severe winds can blow branches and foliage out of the tree, causing more sky than crown to be seen. In most other cases, a thinning crown indicates something wrong with the tree. The foliage could be affected by insects, the bole could be affected by rusts, or the roots could be affected by disease.

It is important to recognize the pattern difference in these two circumstances. If the thinning occurs as a result of storm or mechanical damage, then entire branches are missing, resulting in whole sections missing, showing a clump-like appearance. Illness will show up in the crown evenly and in a lacey pattern. It offers the lacey pattern because the thinning occurs not from lost branches but from lost or sick needles, leaves, and smaller branches. In this case, the tree also ordinarily shows some yellowing of the foliage when compared to the normal tree whose foliage should be thick and green.

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CHAPTER SIXHazard Tree Management

Hazard tree management is the evaluation of and reaction to the trees we encounter. To a parent taking a child to a park or camp, hazard tree management is probably not an issue. The parent should be able to assume that the managers have taken the necessary steps to make the park or camp safe for their visit. The same should be true for private parks and recreation areas.

On some occasions, we must make hazard tree management our own responsibility. On a camping trip, for example, we should not pitch our tent under a dead, leaning tree during a storm. Trees near our homes are our own responsibility. We can learn about tree safety and evaluate them ourselves or we can have them evaluated by a professional. In some cases, we may have to contact a neighbor regarding a tree posing a threat from across property lines.

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Managers of outdoor use areas with standing trees have a special responsibility – the management of those trees with the safety of visitors and staff as a primary objective.

Trees are an integral part of any outdoor use area, but like any other living thing, they require maintenance. As the number of visits around and under them increases, the chance of an accident increases.

Hazard tree management is needed any time there is a tree within striking distance of a human concern or places people live or visit. In some cases, hazard tree management involves no more than a brief look up into a tree to realize that there is no hazard. In some cases an expert forester or arborist is needed to determine if a certain tree is a threat, for example, to identify hidden defects in a tree where people congregate.

Any time trees and human safety are a concern, hazard tree evaluation and management should take place. Hazard tree management should be conducted in camps and campgrounds, parks, roads and trail corridors, picnic areas, around lodges and cabins, and, of course, around homes. An analysis of the potential for tree failure against potential for damage to persons or property can prevent an accident.

If having trees in the area being evaluated is not important, then a liberal approach to hazard tree management can be taken. Cutting down all the trees is certainly an effective method of ensuring safety. If trees are appreciated and retaining them within the

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community is important, then even though it is more difficult, a balance can be achieved between living safely with trees and enjoying their aesthetic qualities. In some cases, such as in a young stand or grove of trees, there is not much to be done in providing for safety; there is little threat. In some cases, such as in a mature or over-mature stand, much evaluation and treatment is needed. There is usually a threat in this case.

In most cases where there are trees, usually a certain percentage has defects. The younger the tree or the forest, the less defects. The older the tree or forest, the more defects, and therefore the more hazards.

Storms play a very significant role in affecting hazard trees. Most tree failures occur during storms. Storms do serve as positive task. They “mop up” hazards created by human activity or by other natural events such as previous storms. Weak and hazardous trees are forced to fail, and dead branches are dislodged during a predictable time, the storm event.

Storms also create additional hazards as well as weakened situations that may or may not wait for the next storm. Roots/soil relationships are interfered with. Trees’ boles are cracked, split, or placed under pressure from bending. Limbs are also cracked or split, sometimes broken but being held by a thread. Depending on the severity of the crack, split, lean, or break, a slight breeze may be all that is necessary to cause complete failure. Some of these failures occur during perfectly calm weather. Widowmakers are the

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most common, but leaning trees are a close second, especially if there is decay in the root systems. If decay is involved, failure is only a question of time. If, for example, a leaning tree has decay in its roots, then the tree continues to grow while the decay in the roots continues to spread. This situation results in more weight being added to a failing root support system. Failure of that tree is simply based on the increasing weight of the tree and the decreasing strength of the roots and, of course, weather.

The National Park Service maintains as its policy that “the saving of human life will take precedence over all other management as the Park Service strives to protect human life and provide for injury-free visits.”

If other parks, camps, and campgrounds adopt this attitude, how will we know when we have achieved our goal of protecting human life and providing for injury-free visits? By compiling a well thought-out plan that includes a close look at each tree that is within striking distance of something we care about or where people are involved. If this is done properly, then hidden defects are the only unknown or unreliable factor. Managing for hidden defects is beyond the scope of any responsible manager. We cannot manage what we cannot see. Accidents will always happen, but through responsible management and removing the accidents-waiting-to-happen, we can minimize the risks.

If we have a tree leaning over our home or a trail and it fails, injuring someone, can we say that we strive to protect human life?

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HAZARD TREE MANAGEMENT PLAN

A good hazard tree management plan should be established by a professional forester or arborist or by the most qualified people the organization has available. In some cases, a professional can train the staff who then can write and manage the plan. The plan should start with goals and objectives, then field evaluations, and succeeding treatments, if necessary. The plan should be written with good records of activities and dates. Follow-up evaluations should be done on a routine basis, at least annually, as well as after storms. A map of the facility is a necessary tool. It can specifically identify and record problem areas. Any tree within striking distance of a use area should be analyzed.

Evaluations

Evaluations in areas with few trees can be done with a single survey. Evaluations in areas with a large amount of trees should be done in two phases. The first phase is to identify level one hazards only. After those are identified and treated, then a second survey is conducted to identify the level two hazards. These trees will require the most consideration.

Decisions have to be made as to whether to remove, modify, monitor, or avoid certain trees. Specific evaluations should be made as to why the tree is less than normal, what the potential damage is, and what action is taken to prevent this potential failure or damage from occurring.

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Chapter 5 “Indicators” should be used as a guide for what to look for, and this chapter should be used to prioritize the information gathered.After level one hazards are removed, proper evaluations, considerations, decisions, and planning for the remaining trees can begin. The level three, or normal, healthy trees should be evaluated for whatever outside factors can affect them (e.g., fire, disease, other trees, and damage from people and their various activities). Protective measures for preserving the health and integrity of these trees should be considered.

Considerations

A tree’s age is a very important factor in its probability of being a hazard. During the 1920s and 1930s most of western Washington state was logged for its timber. About a third of this logged area naturally regenerated a species known as red alder. The lifespan of red alder is sixty to eighty years. Today, in the year 2003, there are many camps, campgrounds, parks, homes, trails, and woods functioning among these over-mature, dying, and dead trees, and accidents are happening. Some recreation site staff prudently treat the situation, and some feel that no action is necessary.

It is important to know the age of the trees under consideration and their expected lifespan. As trees approach maturity, branches start to die and fall, disease has had a chance to wreak havoc, and earlier defects are now poised to cause failure.

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Adjacent trees can present information about any tree under consideration. Some diseases spread from tree to tree. Insects attacking certain trees can move to others. Activities such as roads, trails, campsite construction, and utilities installation and maintenance, can damage trees – particularly the roots and lower bole. It is almost certain that one pathogen or another will infect any sizeable exposed wound, resulting in a progressively weaker tree.

Potential Hazards

Most trees with the potential to cause injury or damage show signs of that potential. Large trees within striking distance of a structure or human activity should be checked for these signs routinely. If the tree presents signs of defects that indicate a high potential for failure and, therefore, harm, there are three ways to avoid disaster:

1. Modify the tree2. Remove the tree 3. Avoid the tree during those times when weather

factors increase the potential for failure beyond an acceptable level of risk. (This may save a life but offers no protection to a structure).

Damage from tree failure is preventable. In the past when a tree damaged property or hurt or killed a person, it was considered an accident or an act of God. This attitude has changed since we realized that there is a certain level of predictability in tree failure. In most

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cases, something can be done to prevent the damage or failure.

For example, twenty years ago cars traveled park access roads sporadically, giving failing trees across the road space between cars to fail with a slim chance of striking one. Today there is a steady stream of cars on most days. Failed trees across roads are regularly causing injury to people and damage to cars.

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Tree Failure

There are three ways in which a tree fails:

1. Failure of the roots and soil2. Failure of the bole or stem3. Failure of the limbs and branches

There are two types of tree failure – complete and incomplete. Complete failures are more common in severe storms when trees are overwhelmed and fall over. From a hazard tree standpoint, a complete failure has done its damage and is no longer dangerous to humans. Incomplete failures occur when a tree leans or loses limbs. An incomplete failure is more dangerous to human beings because a leaning tree or dangling branch can fall on a person or building during a storm. With time, a leaning tree may grow so weak it will fall over without any outside force.

Likewise, there are different kinds of limb failures – a limb can partially break off and hang by a thread, break off and be held up by other limbs, or be severed completely and fall to the ground. In this sense, there is also complete and incomplete limb failure, and again, the incomplete limb failure poses more of a threat to human beings.

Incomplete failure occurs when the tree has been damaged, and is in an unstable situation. Not all incomplete failures result in complete failures. In most cases, partial failure increases the hazard that the tree poses. Its potential to do harm is greater than when the

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tree was standing in a normal vertical stance. Some trees do regain their balance by growing new limbs, callusing over their wounds, or using new growth to create as much balance as possible under the given circumstances. These recovered trees will be a lesser hazard, but will always be more hazardous than a normal tree.

Examples:

1. A branch breaks off and is hanging by a few fibers 2. A tree loses its battle with the wind only partially

and leans at an angle over a home 3. Wind bends or lightning cracks or splits the bole of a

tree and leaves it upright4. The tree is pushed over just enough to break some

roots, remaining upright and possibly leaning.

Predicting whether a specific tree will fail is difficult because there are many variables. Some variables allow us to be able to predict, with a high level of accuracy, trees that have the potential to fail. There are minor variables that, when combined, will cause a tree to fail, as well as single significant factors that can spell failure. Most trees challenged by a 100-mile per hour wind have a high potential for failure. Add wet soil or defective roots, and the potential for failure goes even higher.

Treatment

Treating hazardous trees involves choices. The first choice is whether to treat the hazard or to remove the

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threatened activity. For example, a trail passes under a tree with large limbs attached to a defective bole. The tree is deemed a level one hazard, because the potential for limb or bole failure is very high. But the tree has significant meaning to the organization. The choices are to either remove the tree or to reroute the trail beyond the striking distance of the tree. A tree can be honored from a short distance.

Other than removing a tree in its entirety, the remaining choices are pruning to remove certain branches or limbs or topping to remove the uppermost portion of the tree. The reasons for pruning are to remove dead, diseased, or otherwise hazardous material and to reduce the sail. Topping can reduce the striking distance as well as reducing the sail.

Monitoring and pruning on a regular basis to control limb growth eliminates additional hazard. Monitoring at least every three years (preferably less) and re-pruning before the new growth expands to unmanageable sizes can prevent large limb growth and have the added advantage of sculpting and shaping the tree. Topping can be used when a large tree is within striking distance of a human concern. The tree can be topped short so it will not make human contact if it fails. With this in mind, pruning and topping can be used as a valuable tool in the safe management of trees, especially in those cases where the tree has significant social and aesthetic value. The problem with pruning and topping is that, similar to mechanical damage, they expose wounds for pathogens to infect. Once a tree receives any sort of treatment such as pruning, monitoring becomes

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imperative. We should not expect that if a tree has defects that are treated with a pruning program that our concern ends there.

Logically, pathogenic activity can be controlled by physically blocking the pathogens from the tree’s wound. There are no known proven treatments for blocking or preventing pathogens from infecting trees’ wounds. Paints, and some chemicals, work on occasion. Perhaps instead of attempting to control the whole situation we should aid the tree’s natural processes. But using chemical applications to stave off pathogens may also interfere with the tree’s natural processes.

Certain trees use pitch over a wound as a physical barrier to invasive spores; artificially treating a wound should not interfere with this process. It is logical, then, that duplicating or aiding the tree’s natural efforts over a pruning or other wound would help the tree in its fight against infection. The downside is that if the pathogen infects the wound first, then a barrier on the wound will seal it and the infectious medium. Even if one pathogen infects a wound before a barrier is applied then the barrier will still block out other pathogens, and if a pathogen infects a wound, adding a barrier or not will not change the fact that the tree was infected. While this may not stop all pathogenic invasions, it is a big step in prevention. Furthermore, if limbs can be kept from growing large, then a certain amount of rotting bole can be tolerated. Re-pruning can also remove infected areas of trees years after the initial pruning or topping.

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If the goal is to keep as many existing trees as possible, and pruning and topping enable us to do this, they should be considered appropriate methods of hazard tree control. Topping with regular monitoring and re-pruning can turn a hazardous tree into an aesthetically pleasing tree that is relatively safe.

Pruning can be used: 1) To open a tree crown, allowing wind to pass through

the tree and reducing the sail effect of the crown; 2) To balance a tree’s structure. If a tree has been

damaged, pruning can be used to re-create a new balance in the tree’s structure. If two trees have been growing close together, there will be very little foliage in the area between them. If one of them is removed, the remaining tree will have a one-sided crown. Pruning could re-create the balance.

3) To reduce the striking distance of a tree. Pruning and topping of trees duplicates natural functions. A good percentage of trees in a natural environment receive similar treatment from weather.

Certain species of trees such as western hemlock do not respond well to treatments such as pruning, while some species such as Douglas fir immediately start spewing pitch over wounds. Species that do not respond well to pruning are poor candidates for retention where people are present.

In some cases, pruning and topping only postpones the inevitable that the tree is going to die or will sooner or later increase its failure potential so as to achieve a level one rating.

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A consideration should be given to immediately planting young trees of a species well suited to the vicinity and the use of the area. Encourage the kind of care that results in a healthy tree and consider this a replacement for the defective and hazardous tree that had received treatment.

Good forest management should be an integral part of any hazard tree treatment program. The primary goals of most forest management plans are to grow healthy, thrifty trees and also to remove the defective, diseased trees, replacing them with healthy, vigorous ones. A hazard tree plan has similar goals. It promotes healthy trees; removes the defective, hazardous trees; and replaces them with healthy, non-threatening trees.Balance can be reached between the aesthetic value of trees and the potential damage or injury that they can cause. The dilemma for managing trees in an outdoor use area usually involves the role of trees in the presentation of the area versus the responsibility a facility has regarding safety. Invited guests have the right to expect that the organization has made the facility safe for their visit.

It is not always necessary to remove all defective trees, but it is always necessary to monitor them, as defective trees do survive storms. But as the value of the concern to be protected increases, the level of treatment should also increase.

Hazard Tree Management

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Hazard tree management is needed any time a tree is within striking distance of a human concern, or places people live, visit or travel. From simply guessing if a tree along a road might fall onto a passing car to logically assessing the pathogenic activity inside a tree, if human safety is a concern, then hazard tree management should be conducted.

In an established recreation site such as a park or camp, a methodical system for analyzing the risk from trees should be established. The system should be simple and easy to understand. There is no need for a hazard tree evaluation and rating system to be complicated; the tree either has a problem or it does not. If a tree has a rotting bole, in a hazard tree sense, it is not important which pathogen caused the rot; the only consideration is under what circumstances will this tree fail, and if the tree or part of the tree fails, what are the potential damages. The particular pathogen is a definite consideration in a secondary sense, to determine if the disease will or will not spread to other trees and what part of the tree will be affected in the future.

A dead tree leaning over a well-traveled road or trail can fail at any time, and when it fails it may do significant harm. This tree should receive the highest level of hazard tree rating. A live tree with a hollow cavity in its bole standing along the same road can be spared from the cutter’s saw if the road or trail can be avoided during a storm capable of causing its failure. This tree may receive a low level hazard rating.

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In any given stand of trees there is usually a certain percentage of defective trees. Trees fail as an ordinary function in forests, but they usually fail during storms, unless they have surpassed a certain threshold of defects. Once trees have surpassed this threshold then their failure can occur during ordinary weather; in some cases they even fail on perfectly calm days.

The goal of any hazard tree rating system should be to determine a threshold of defects in trees that increase their chances of failure to an unacceptable level and treat those trees. The other trees may be retained and managed. To manage hazard trees that do not pose an immediate risk is to treat, monitor, and conduct follow-up treatment when necessary. A part of this plan may include avoidance during storms severe enough to cause the tree’s failure.

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THE HAZARD TREE RATING SYSTEM

The goal of the hazard rating system is twofold: first, to determine which trees are a threat to human concerns; and second, to determine the level of treatment, if any, needed for those trees which are determined to be a threat. This information is also sufficient for determining whether immediate treatment is necessary or if the tree should be monitored.

All trees within striking distance of human activity should be evaluated; there is less need to evaluate trees that do not have the potential to damage human beings or their concerns.

Even though any tree can fail given the right circumstances, certain trees are considered a threat to human concerns because of their location and/or their structural integrity. Trees that are considered a threat to human concerns include those trees that have a higher than normal potential for failure; a three tier system is used to assess the risk.

Hazard Level 1 - TREES WHOSE FAILURE COULD OCCUR IN ORDINARY WEATHER OR A MILD STORM.

Examples:! Any tree or part of that tree that is dead or decayed. ! Severely leaning tree.! Slightly leaning tree that is defective.! Tree with weak, defective or diseased root system. ! Mushroom-like growth (conks) associated with the

tree.

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Level one hazard trees should be removed or modified so that the hazards are corrected or improved. A dead tree should be removed or avoided; dead branches over an activity site should be removed, and the tree should be monitored.

Activity within striking distance of the tree should be conducted with caution until the tree is removed or upgraded to a level two hazard tree.

Hazard Level 2 – TREES THAT WILL PROBABLY SURVIVE A MILD STORM, BUT ARE LIKELY TO FAIL DURING A SEVERE STORM.

Examples:! Slightly leaning trees that are top heavy.! Trees with defective branches.! Trees with slight root system damage or decay.! Trees with forks, crooks, spike branches, and

multiple stems.! Trees with cavities and holes.

All level two hazard trees should be monitored routinely. An initial evaluation should record the tree's present condition and serve as a basis of comparison for all future inspections.

Hazard Level 3 - NORMAL TREES. THERE ARE NO DEFECTS, AND THEY ARE GENERALLY SAFE. HOWEVER, CAUTION IS APPROPRIATE UNDER SEVERE STORM CONDITIONS.

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Under severe storm conditions, all trees have the potential for failure. A large, defect-free tree with normal failure potential should be treated as a level one hazard during a severe storm if it is within striking distance of humans or human concerns. The perfectly healthy tree can fail due to storm severity and should be respected as a high risk during severe storms.

Helpful Hints

Most individuals can without training read signs in trees that indicate danger.

" Look at your trees routinely. If there is a threat, it is usually obvious.

" Become aware of local wind history and pattern." Analyze trees in areas visited that are large enough

to inflict harm." Mushroom-like growth or insects on trees may be an

indication that the tree is not well." Large, longitudinal cracks on the outer surface of

trees indicate damage or instability." Avoid widowmakers. A small branch falling from a

height of fifty feet can maim or kill." Disturbance in a tree’s form may be an indication of

an unsound tree." Avoid leaning trees, particularly during storms." Have your trees of major concern evaluated by a

professional." If you prune or top a tree, monitor it on a regular

basis." Take responsibility for your own safety.

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THE EFFECTS OF STORMS

Storms are responsible for most of the negative impacts on trees. They break branches; they force trees to lean; they bend them until they break; they disturb root systems; they break out tops. This causes trees to fail, consequently damaging other trees on their way to the ground.

Human activities are also responsible for some of the negative impacts on trees. We drive spikes and drill holes, we girdle boles, we disturb root systems, and we change the natural alignment of stands of trees.

For the most part, human activities set up the potential so that storms can have a more remarkable effect on trees. In some cases tree failure is simply an overwhelming force from a storm causing a perfectly healthy tree to fail. For the most part, our activities, previous storms, pathogens, and mechanical damage establish a tree’s weakened situation, and the storm completes the job.

Consequently, a prudent tree owner or manager conducts a tree damage assessment after a storm. This assessment should be carried out after windstorms, ice storms, snowstorms, and even heavy rains or floods. Something as simple as a broken branch above a walkway is worth looking for.

What to look for (refer to chapter on indicators beginning on page 45):! Leaning trees

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! Hanging branches ! Broken branches ! Cracks in trees ! Disturbance in the soil around trees.

If a tree does not fail during a storm, it can use that experience to strengthen itself, given that the damage was not insurmountable and there is sufficient recovery time. A tree can recover from bending that does not cause a split, crack, or break. It can also recover from losing its bond with the soil as long as significant lean has not occurred. But any injury that exposes wood fiber to pathogens or any severe lean is a reason for evaluation and possible treatment.

Recreation site managers must consider both the aesthetic qualities that the trees offer their guests as well as the safety of those guests that the same trees may threaten. Hazardous trees should not be about liability; the consideration should be safety.

The skills and the knowledge are available to identify and to correct hazardous tree situations. Identify areas of concern anywhere that people may visit and trees are present. The areas should include trails, roads, structures, and gathering places. Designate a “safe area.” If a severe storm develops suddenly, guests should have a safe refuge from falling trees or flying branches. A structure capable of holding the ordinary amount of guests with no hazardous trees within striking distance would be ideal. The dining hall has served some recreation sites very well after ensuring that no threat from failed trees exists around the structure.

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If trees exist on a recreational site, the potential for failure exists. Therefore the potential for injury also exists.

All visitors should be informed of the potential hazards and how to avoid them. Furthermore, they should be informed as to what to do or where to go if a sudden storm develops with sufficient intensity to challenge the trees’ stability.

Striking Distance

Striking distance refers to the probable horizontal reach of a tree should it fail. Trees within striking distance of human concerns should be evaluated and monitored for hazards and failure potential. Trees outside of striking distance of human concerns may not need to be evaluated. Dead or failing trees make good wildlife habitat and may safely be left provided that they are out of range of human concerns should they fail.

Measuring the striking distance can easily be done with an instrument that measures vertical angles, such as a clinometer. From the area of concern, the angle to the top of the tree under consideration and the angle to the base is measured. These angles can be measured either in degrees or percent (see table on page 117). Keep in mind that the vertical angle is measured from the eye,

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which is five or six feet above the ground, depending on the height of the person doing the measurements.

On flat topography, the striking distance of a tree equals its height. If the percent angle to the base of the tree is near zero and the percent angle to the top of the tree is 100% or greater, the tree is within striking distance (see table on page 118).

Measuring the striking distance of trees on sloping topography requires the same two measurements. If looking uphill, subtract the angle to the base of the tree from the angle to the top. If the difference is 100 or more, the tree is within striking distance. If looking downhill at the tree, add the angle to the base of the tree and the angle to the top. If the sum is 100 or more, the tree is within striking distance.

As a precaution, it is wise to add on to the striking distance calculated to account for the natural variability. Trees sometimes pivot forward using their branches or slide down hillsides when they fall. They can break up and bounce parts downhill. Storms can also extend the striking distance. The steeper the slope, the greater effect it has on the striking distance. Adding twenty feet to the calculated striking distance is adequate for most practical purposes.

These calculations are based on relatively vertical trees. Adjustments should be made for leaning trees. If a leaning tree fails, it will almost certainly fall in the direction of the lean. Calculating the striking distance of leaning trees requires knowledge of the tree’s height.

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CONVERSION TABLEFOR

VERTICAL ANGLES

DEGREES PERCENT5 96 109 1510 1811 2014 2515 2617 3019 3520 3622 40

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24 4525 4626 5029 5530 5831 6033 6535 7037 7539 8040 8441 8542 9043 9545 10050 11851 12055 143

60 173

A tree is within striking distance if

the % angle to the base is

and the % angle to the top is equal to or greater than

+100 200 +90 195+80 185+70 170+60 150+50 145

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+40 140+30 130+20 120+10 1000 100-10 95-20 90-30 80-40 70-50 70-60 60-70 50-80 50-90 45-100 35

Note: This table refers to the geometric reach of a vertical tree. It does not apply to leaning trees or the

effects of storms or topography.

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AVERAGE HEIGHTS OF NORTH AMERICAN TREES AT MATURITY

Under 50 Feet

Flowering dogwood PersimmonHackberry PinyonHolly SassafrasJuniper Vine mapleMagnolias Virginia pineNorthern white cedar WillowsPacific yew

50 to 75 Feet

Basswood Lodgepole pineBig-cone Douglas fir Northern red oakBlack cherry Oregon ashButternut Oregon white oakCatalpas Quaking aspenEastern red cedar Red pineHoney locust White ashKnobcone pine

75 to 100 Feet

Alaska cedar California laurelAmerican beech Eastern white pineAmerican chestnut Golden chinquapinAmerican sycamore HickoriesBigleaf maple Jack pineBlack locust Jeffrey pine

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Black walnut Loblolly pineBlue spruce MadroneBuckeyes Monterey pineMountain hemlock Subalpine firPaper birch Sugar mapleRed alder Sweet-gumRed maple Tan oakShortleaf pine TupelosSilver maple White oakSlash pine

100 to 150 Feet

American elm Longleaf pineBald cypress Noble firCalifornia red fir Pacific silver firCottonwoods Western larchEngelmann spruce Western white pineGrand fir White firIncense cedar Yellow poplar

Over 150 Feet

Douglas fir Sitka spruceGiant sequoia Sugar pinePonderosa pine Western hemlockPort Orford cedar Western red cedarRedwood

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SHADE TOLERANCE OF NORTH AMERICAN TREES

Shade Tolerant – Able to grow in shade

Alaska cedar Chamaecyparis nootkatensisAmerican beech Fagus grandifoliaBasswood Tilia spp.Bigleaf maple Acer macrophyllumBuckeyes Aesculus spp.California laurel Umbellularia californicaEngelmann spruce Picea engelmanniiFlowering dogwood Cornus floridaGrand fir Abies grandisHolly Ilex spp.Incense cedar Libocedrus decurrensMountain hemlock Tsuga mertensianaNorthern white cedar Thuja occidentalisPacific silver fir Abies amabilisPacific yew Taxus brevifoliaPersimmon Diospyros spp.Port Orford cedar Chamaecyparis lawsonianaRed maple Acer rubrumRedwood Sequoia sempervirensSilver maple Acer saccharinumSitka spruce Picea sitchensisSub-alpine fir Abies lasiocarpaSugar maple Acer saccharumTan oak Lithocarpus densiflorusTupelos Nyssa spp.Vine maple Acer circinatumWestern hemlock Tsuga heterophylla

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Western red cedar Thuja plicataWhite fir Abies concolor

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Intermediate – Able to grow in some shade but requires open sun to thrive

American chestnut Castanea dentataAmerican elm Ulmus americanaAmerican sycamore Platanus occidentalisBald cypress Taxodium distichumBlue spruce Picea pungensCalifornia red fir Abies magnificaDouglas fir Pseudotsuga menziesiiEastern white pine Pinus strobusGiant sequoia Sequoia giganteanGolden chinquapin Castanopsis chrysophyllaHackberry Celtis spp.Madrone Arbutus menziesiiMagnolias Magnolia spp.Monterey pine Pinus radiataNorthern red oak Quercus rubraOregon ash Fraxinus latifoliaSlash pine Pinus elliottiiSugar pine Pinus lambertianaWestern white pine Pinus monticolaWhite ash Fraxinus americana White oak Quercus alba

Intolerant – Requires open sunlight to grow and thrive

Big-cone Douglas fir Pseudotsuga macrocarpaBlack cherry Prunus serotinaBlack locust Robinia pseudoacaciaBlack walnut Juglans nigraButternut Juglans cinereaCatalpas Catalpa spp.

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Cottonwoods Populus spp.Eastern red cedar Juniperus virginianaHickories Carya spp.Honey locust Gleditsia triacanthosJack pine Pinus banksianaJeffrey pine Pinus jeffreyiJuniper Juniperus spp.Knobcone pine Pinus attenuataLoblolly pine Pinus taedaLodgepole pine Pinus contortaLongleaf pine Pinus palustrisNoble fir Abies proceraOregon white oak Quercus garryanaPaper birch Betula papyriferaPinyon Pinus edulisPonderosa pine Pinus ponderosaQuaking aspen Populus tremuloidesRed alder Alnus rubraRed pine Pinus resinosaSassafras Sassafras spp.Shortleaf pine Pinus echinataSweet-gum Liquidambar styracifluaVirginia pine Pinus virginianaWestern larch Larix occidentalisWillows Salix spp.Yellow poplar Liriodendron tulipifera

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GLOSSARY

Blister – a scar on a tree that manifests itself as a weeping sore; it may weep pitch or other colored liquids

Bole – a tree’s stem supporting the limbs and crown

Broom – an abnormal clustering of branches associated with infections, genetic aberrations, and insect damage

Butt – the part of the tree’s bole closest to the ground

Buttressing – an adaptive technique normal trees have acquired in response to wind exposure; consists of growing extra fibers in a braided pattern, usually at the base of the bole or nodes

Butt rot – decay developing in and sometimes confined to the butt; may originate in wounds or roots; root disease which has left the roots and entered the bole

Callus – tissue produced at wound sites in response to injury, which may or may not overgrow an infected area

Canker –a definitive lesion on a stem, branch, or root

Canopy – the uppermost shade-producing foliage in a stand of trees

Chlorosis – an abnormal yellowing of foliage

Compaction – the compression of the soil that displaces the air space between the soil particles

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Conk – the fruiting bodies of many wood-decaying fungiCore sampling – the removal of a small sample of a tree’s woody interior for examination

Crook – a sharp offset in the lineal alignment of a tree’s bole

Crotch – that part of the tree where the main stem or larger branches fork

Crown – the uppermost part of any tree containing the branches and foliage

Crown closure – the amount of light that a tree’s crown blocks out from the naked eye

Decay – biodegradation or decomposition by fungi and other microorganisms

Defect – any feature, fault, or flaw that lowers the strength, integrity, or utility of an affected part of a tree

Distress cones – smaller-than-normal, excessive in number cones produced by a tree under stress

Drip line – the maximum radial extension of the tree crown projected to the ground

Failure – partial or total collapse of a tree or tree part

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Fibrous root system – root system in which the tree produces no central root

Fork – a tree’s bole separated into two new stems; also known as school marmFrass – sawdust-like material on the bole or at the base of a tree produced by insects chewing and excavating the bark or woody tree fibers

Frost cracks – splitting of the outer bark and sapwood which occurs on the boles of trees subjected to extreme cold; usually indicate decay inside the bole

Fruiting body – conk, mushroom, or other fungal reproductive structure

Gall – a swelling on a tree’s limb produced by fungi or bacteria or infested with gall-forming insects

Hazard tree – any less than normal tree that is within striking distance of humans or their concerns

Heart rot –decay restricted to the heartwood

Holding strength – the structural relationship between the roots and soil particles

Human concerns – human beings and their property

Hypha – a single, microscopic, thread-like filament made up of fungal cells

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Inoculum – spores or tissue of a pathogen that serve to initiate disease

Jackstraw – trees laying on the ground intertwined in all different directions

Leader – the last year’s vertical growth on a normal tree

Lower bole – the part of a tree’s bole closest to the ground

Mechanical damage – non-biological damage to a tree, such as damage from equipment

Node – the junction of two woody portions of a tree, e.g., limb to bole or limb to limb

Pathogen – a fungus, bacterium, virus, or other infective agent capable of causing disease

Plant association – a system of classifying plant communities

Punk knots – a protruding and unhealed knot of a tree with decay (bark may not encase the knot)

Root collar – the protruding root-like structures along the groundline at the base of a tree formed by some trees

Root crown – the region where the root system joins the bole

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Root graft – the process in which the roots of two or more trees of the same species come in contact and grow together and share a root system

Sail – the one-dimensional surface area of a tree’s crown and bole

Scar – a partially callused over wound on a tree

School marm – see fork

Seam - a long, narrow wound that has been callused over by a tree; where callusing growth from both sides of the defect meet.

Shake – a defect of trees which are commonly exposed to high winds; the bending from wind causes the growth rings to separate

Signs – indicators of the presence of defects in a tree

Snag – a standing dead tree

Spike knot – the loser of a competition in which two limbs vie for dominance after the break of a tree’s bole; the losing limb becomes a spike knot if it’s broken

Spike limb – the loser of a competition in which two limbs vie for dominance after the break of a tree’s bole; the losing limb becomes a spike limb if it’s still alive

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Split – a long, narrow rupture in a tree’s bole that does not result in a complete break; usually caused from bending

Stem – the main trunk or central stalk of a tree

Striking distance – the probable horizontal reach of a tree should it fail

Sweep – a gentle change in direction of a tree’s bole; a slight bend in the bole

Taproot system – root system in which the tree produces one central root that penetrates the soil vertically and spreads out at a depth determined by genetic predisposition and the composition of the soilTopping – removal of some of the upper crown of a tree

Undermined roots – roots that are no longer firmly anchored due to soil removal or loss beneath and/or around them

Widowmaker – debris or branches suspended in the crown of a tree; may or may not be attached

Wind break – trees that receive the first contact with the wind, creating a void on the lee side

Wind throw – tree failure triggered by wind

Xylem – water conducting woody tissue

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GENERAL RESOURCES

Allen, E., D. Morrison, and G. Wallis. 1996. Common tree diseases of British Columbia. Canadian Forest Service. Victoria, B.C.

Avery, T. E. 1975. Natural resources measurements. McGraw-Hill. New York, N.Y.

Boyce, J. S. 1961. Forest pathology. McGraw-Hill. New York, N.Y.

Brockman, C. F. 1968. A Guide to field identification: Trees of North America.Golden Press. New York, N.Y.

Graham, S. A. and F. B. Knight. 1965. Principles of forest entomology. McGraw-Hill. New York, N.Y.

Harvey, Jr., R. D. and P. F. Hessburg. 1992. Long-range planning for developed sites in the Pacific Northwest: The context of hazard tree management. United States Department of Agriculture.

Hitchcock, C. and A. Cronquist. 1973. Flora of the Pacific Northwest. University of Washington Press. Seattle, W.A.

Kong, E. 2002. “Hazard Tree Management for Camps.” Camping Magazine. Vol. 75, No. 5.

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Little, E. L. 1998. National Audubon Society field guide to trees. Alfred A. Knopf. New York, N.Y.

Pearce, J. K. and G. Stenzel. 1972. Logging and pulpwood production. The Ronald Press Company. New York, N.Y.

Petrides, G. A. 1958. A field guide to trees and shrubs. Houghton Mifflin. Boston, M.A.

Pojar, J. and A. MacKinnon. 1994. Plants of the Pacific Northwest coast. Lone Pine Publishing. Vancouver, B.C.

Spurr, S. H. and B. V. Barnes. 1973. Forest ecology. The Ronald Press Company. New York, N.Y.

Stefferud, A., Ed. 1957. Soil, the 1957 yearbook of agriculture. The United States Government Printing Office. Washington, D.C.

Thies, W. G. and R. N. Sturrock. 1995. Laminated root rot in western North America. United States Department of Agriculture. Portland, O.R.