1
Arboriculture and Tree Energy Dynamics:
Understanding the Maturing Tree
Rex A. Bastian, Ph.D.
The Davey Tree Expert Co.
Wheeling, IL 60090
Consider Trees as a System
� Orderly collection of
parts
� Produce a service
� Require constant
supply of fuel
� Cannot become larger
than the energy
available to power the
system
To Understand How to Care for Maturing Trees, We Must:
� Understand stress and how it affects trees
» To do this, we must also understand:
–Tree anatomy and how trees grow
–The processes of respiration,
photosynthesis transpiration, and
translocation
� Understand how trees allocate resources
-Merker and Hopper, 2005
System Must Maintain “Order”
� “Order” for a tree
translates into
“health”
� As “disorder”
enters the system
» Health
– Stress (reversible)
– Strain (Irreversible)
� The “System”
demands energy
2
Energy Required for Every Little Thing
� Stomata Function
» Doesn’t just “happen”
– Closing of leaf stomata
reduces transpirational
water loss
� Also limits carbon
dioxide and water
needed for
photosynthesis
� Also limits oxygen
needed for respiration
Opening- Left and closing- right; http://bio.fsu.edu/ www.gopixpic.com
Tree Begins with Energy Reserve
� More energy
needed as tree
grows to start
the system
each year
Energy Determines the Ultimate Size of the System
� You can start with a
healthy, small tree
and keep it healthy
and small
� Can’t take a healthy
large tree and turn it
into a healthy, small
tree
Tree Physiology
� The study of processes
that take place inside at
tree
» Photosynthesis
» Respiration
» Transpiration
» Absorption
» Translocation
» Growth and Development
» Defense
3
Photosynthesis
Chlorophyll (Leaves and
Green Twigs)
Carbon Dioxide
(Air)
Oxygen (Air)
Water (Soil)
Light Energy
Light Energy
ChlorophyllWater + Carbon Dioxide Sugar + Oxygen + Water
12 H2O + 6 CO2 ���� C6H12O6 + 6O2 + 6H2O
What Happens to the Sugar?
� Much is used as a kinetic energy source for
respiration
» fuels day to day processes (makes things happen)
� Chained together to make “Cellulose”
» more leaves, roots, wood, etc.
� Chained together to make “Starch”
» stored for future energy needs as carbohydrate
reserves ( Potential Energy )
� Used for fuel to make protective chemicals
Respiration
Sugar + Oxygen Energy + Water + Carbon Dioxide– Reverse of photosynthesis– Sugars are burned to produce kinetic energy for use– Occurs both day and night (even when trees are dorm ant)– Ultimately, this becomes the key process
Purves et al., Life: The Science of Biology, 4th Ed.
TranspirationPulls Water Up Stem
� Loss of water through the foliage in the form of water vapor» As water vapor is lost, water
molecules “pull” each other up the plant
» Direct connections exist from root hairs to leaves
» Rate of water loss is regulated by stomates
– Usually open during day and close at night
» Temperature, humidity, light and other factors all influence transpiration
4
Absorption/TranslocationWater Moves into Root By Osmosis
� Plant cells have more solutes in their interior than does water in the soil» Water moves from low
solutes to high solutes– Same principle as used
in pickles or salted meats
» Requires no or little energy» Once water reaches xylem
tissues in root, transpiration pulls water molecules up the tree
Direction of water movement
MembraneDissolved Solutes
Absorption/TranslocationPassive and Active Uptake of Nutrients
� Passive Transport -
movement of nutrients from
higher to lower
concentration (Diffusion)
� Active Transport - root
selectively transports
nutrients across plasma
membrane and into the root
against concentration
gradient
» Requires Energy
Translocation
� Food (sugars and other compounds) are
moved in phloem tissues
» Sources (where made)
– Leaves/green twigs
» Sinks (where needed)
– Fruit
– Seeds
– Young foliage
– Root tissues
� This movement can be up, down, or
sideways in the tree» Loading the phloem requires energy
� The phloem, like the cambium, is very
thin and easily damaged
Growth
� Tree Growth depends on two “pumps”
» One produces water and elements
» The other produces energy
� Each depends on the other
» If one begins to fail, the other will soon follow
� Growth and health depend on how well both pumps can function together as
the tree grows larger, demanding both more potentia l and kinetic energy
Water and Elements
Energy
Image Courtesy of the Morton Arboretum
5
Trees are Generating Systems
� They must grow to
survive
� They can grow fast
or slow, a lot or a
little, but they must
grow
» They have no choice
� If trees stop
growing, they die!
Photosynthesis Vs Growth Vs Defense
� Can there be
too much of a
good thing?
� What about the
low/moderate
range?
How Does Nature Handle the Situation?
Trees Allocate Resources
» Metabolism
» Growth
» Reproduction
» Defense
� Tree must finance all of these
� Maintaining a high level of
potential energy is key to long
term health
Growth Strategy and Life Expectancy
Growth
Defense
Storage
� Trees allocate energy to
growth and defenses
differently
� Resulting life expectancy
vary based on growth
strategy
» Poplars ���� 60 years
– “Live Fast, Die Young”
» Oaks ���� 200-300 years
– “Slow and Steady Wins
the Race”
GrowthDefenseStorage
Fast Growth Tree Species
Slow Growth Tree Species
Quandary--Which is More Desirable?
6
Resource AllocationUnequal Incomes
GrowthDefenseStorage
GrowthDefenseStorage
� The tree with the
greater income
can allocate more
to each use, but
maintain the
balance
Tree Defense SystemsCODIT
� CODIT can be hard to visualize» Key points
– It’s a survival mechanism– Wood that forms after
wounding is more resistant to decay
– Trees may become hollow as a result of CODIT
– Decay spreads vertically faster than sideways and outward
� Requires Energy, but is funded at low priorityUSDA Forest Service
Prioritization of Resources
1. Maintenance of living tissues (Respiration)
2. Production of fine roots
3. Flower and seed production
4. Primary growth (elongation of shoots and roots)
5a. Secondary/Diameter growth
5b. Defensive chemicals
Oliver and Larson, 1996
Mass and Energy
� Must consider two different ratios
» Potential to Kinetic Energy Ratio
» Dynamic to Static Mass Ratio
7
Energy Makes and Allows Things To Happen
� Potential Energy
» Reserve (Stored)
– Short term (Checking)
� Glucose
– Long term (Savings)
� Starch Reserves
» Allows system to get
larger
» Maintains kinetic energy
� Kinetic Energy
» Active Energy (Metablolism)
» Pays the bills
– Think Wallet (Cash)
– More leaves, wood, fruit,
defensive chemicals, etc.
» Makes system larger
» Maintained by potential
energy
Growth Beyond Potential Reserves Risks Reserve Depl etion
Dynamic vs Static MassDynamic Mass: Tissues that are alive and functioni ngStatic Mass: Tissues that are dead or not actively functioning
• As Trees Age:– Static mass increases relative to dynamic mass– Potential/Kinetic energy ratio decreases– Demand for carbohydrates increases
– Volume of respiring tissues increases while photosy nthetic volume remains fairly constant
Mass/Energy Ratio
� Small Trees tend to grow faster
� Large trees tend to grow slower
� As trees age, energy requirements
increases exponentially
» Reproduction
» Wounds accumulate
– Require barrier zones
� Larger size means more ability to
produce energy
» More energy needed to start system
each spring
May 25, 2016
July 20, 2016
The Core/Skin Hypothesis
� Trees try to deal with
the energy/mass
quandary
� A Tree is a Series of
Overlapping Trees
» Trees use this principle
to enable them to “shut
down” the “inner” trees
to reduce energy
demands
USDA: Forest Service
Shigo, 1989
8
Tree System Adjustments
� Trees adjust by
reducing dynamic
mass
» Shed parts
» Shut down older,
inner core trees to
form heartwood
� Requires energy
to form, but
afterward, no
energy to maintainUSDA: Forest Service
If Trees Can’t Adjust
� Health gives way
to stress which
can lead to strain
» Decline
–Whole tree
» Dieback
–Part of tree
If It Can Adjust
� May observe a
“reset” of the
trees growth
pattern
» “Turned a corner”
» “Got back on its
feet”
» “New lease on life”
Enough Energy Must Constantly Enter System to Maintain Order
� As Arborists, we
must:
» Understand limits
» Know when added
energy gains little
» Know when to
recommend “pulling
the plug”
9
Tree Age vs. Pruning Dose
� The older, more
mature a tree
becomes, less live
wood and more
dead wood should
be removed
Shigo: Modern Arboriculture
ive wood ead wood
Young
Mature
Over-maturePru
ning
Per
cent
age
Tree Age
D/S Mass ���� HighP/K Energy ���� High P/K Energy ���� Low
D/S Mass ���� Low
Over-Pruning/Construction Injury and Sprouts
� Loss of too many
leaves or injury to
root system can
lead to excessive
shoot formation
» Indicates the tree is
using energy
reserves
» Attempting to return
energy to tree
Liontailing
� “Reverse Topping”
� Removes interior leaves
that function better under
high temperatures
� Leads to overextended,
structurally weak
branches
� Reduces local energy
reserves
Fertilizers Are Not Plant Food
pH Drops
NO3-
HCO3-
HCO3- + H2O = H2CO3 + OH-
pH Increases
NH4+
H+pH Drops
Do not add energy to the system
10
Trees and TurfSo, What Makes the Most Sense?
� Whenever possible, try to separate the two systems» Allows each system to be
managed most effectively
» Avoids the conflicts
� Identify the most important plant group occupying the area, and optimize the management of that group
Trees Are Fighting A Losing Battle As They Age
� The tree is committed to
increasing its mass
� With limiting resources ,
the tree regulates its
dynamic/static ratio so that
kinetic energy demands do
not exceed potential
energy reserves
� It can’t keep doing this
forever!Image from Shigo, Modern Arboriculture
Patterns of Death in Landscape Trees� Structural Failure
– Branch, crown and stem failure, uprooting, decay, girdling
� Environmental Degradation» Acute
– Flooding, fire, vandalism, construction injury, drought, high/low temperature
» Chronic– Soil toxicity, soil
compaction, air pollution, restricted growing space, low fertility, severe pruning
� Parasitic Invasion– Insects, fungi, bacteria,
viruses, mycoplasma-like organisms, parasitic plants
1989
1998
1994
The Decline Spiral
� Predisposing Factor
» Diminishes vitality from optimum
» May not be noticeable
» Long term
» Character of tree or physical
environment
� Inciting Factor
» Especially damaging to Predisposed tree
» Short term
» Often very noticeable
» Physical or biotic
� Contributing Factor
» Perpetuates decline of already altered
tree
» Long term
» Effect often very noticeable
» Often opportunistic insect/pathogenImage/Text from Manion, Tree Disease Concepts
11
The Decline Spiral
USDA Forest
So, Why Do Trees Die?
� And finally, Respiration Terminates
» Which leads to carbohydrate production
ceasing and/or carbohydrate stores being
exhausted
–Then, photosynthesis slows or discontinues
� Factors necessary for photosynthesis are
unavailable, interrupted, or obstructed
» Because of physical, biological, environmental
or human factors
Healthy vs Unhealthy
� May vary by tree part
� The “System” has high energy demands» Limitation on
energy will result in ruthless changes
» Ultimately, the tree runs out of energy
� Understanding that system will make us better arborists
1989
1998
1994
Summary
� Each part of a tree’s anatomy contributes to its survival
� Photosynthesis produces energy, respiration uses that energy, and transpiration keeps trees hydrated
� A tree’s vascular system is responsible for moving water, nutrients, and foods to where they are needed
� Trees defend themselves from insects and diseases, but ultimately, run out of energy