John Ben Wright Oregon State University FES 548 Term Paper Assignment 3/14/16

Ulmus pumila

Introduction Ulmus pumila L. (Siberian elm) is a hearty and tolerant tree species that ranges from its native East Asia to more recent arrivals in Europe and N. America. Its introduction continues to serve a diversity of applications, likely becoming the most introduced tree species in N. America, despite its invasive characteristics. It tolerates temperature extremes, drought, wind, challenging substrates, and thrives in complex and highly disturbed environments. Unlike native elm species in Europe and N. America, it is highly resistant to Dutch Elm Disease. It seeds prolifically, is difficult to kill, and hybridizes with native elms. The very same qualities that make it an ideal survivor for challenging applications such as wind breaks, shelter belts, street trees, shade trees, hedges, and phytoremediation, also predispose it towards invasibility. It’s management, therefore, is a paradoxical effort to harness the strength of those irascible characteristics and limit its presence to only intentional landscapes, knowing full well that from the trees point of view, the ideal condition for success is absence of management.

Ulmus pumila in Gobi Desert, Mongolia Ulmus pumila in Taos, NM (Wikipedia) (JBW 3/8/16)

Biological Characteristics

Ulmus pumila Characteristic Citation

Life Form Tree under higher moisture that tends towards multi-trunk form. Shrub in dryer areas. USDA SW Field Guide

Life Cycle

Seed, Seedling (< 3/8" Diam.), Sapling (3/8" to 2.5" Diam.) , Small Tree (2-3" Diam.), Mature (> 3" Diam.), Senescent. Precocious reproduction capability within 10 years of growth. Depending on conditions, the tree can live upwards of 200 years.

USDA SW Field Guide Dulamsuren 2008 Zalapa 2009

Size Up to 70’ Tall and 50’ Feet wide with slender spreading branches USDA SW Field Guide

Trunk Rough grey brown bark with shallow irregular furrows USDA SW Field Guide

Twigs Silver grey, yellowish, or grayish brown with a leaf bud at each bend. Scattered lenticels. USDA SW Field Guide

Leaves

Alternate – 0.5 to 2.5” Long, tapered at each end with a simple serrate. Upper surface is deep green. Lower surface pale green with hairs along vein axils. Leaves may turn yellow in autumn.

USDA SW Field Guide

Flowers 2 to 5 small green drooping flowers, no petals, occurring February through April before leaves develop

USDA SW Field Guide

Fruit Clusters of smooth, circular, winged samara fruit occurs April to May. Contains single seed. USDA SW Field Guide

Seed

Prolific seeding, primarily through wind dispersal, dormancy not necessary, tolerates intermittent moisture, osmotic stress and high range of temperatures. Dispersal rarely > 100 M. High germination rate for seed. (Wesche study measured 48% fine soil and 72% course soil)

Wesche 2010, Bertolasi et al 2015

Reproduction Mainly sexual, although clonal reproduction is possible when resources are limiting. Dulamsuren 2009

Pollination Pollination Distance is measured up to 7.89 KM with a mean of 2.93 KM Bertolasi et al 2015

Life Cycle Thresholds Seed The infamous seeding habit of U. pumila may be necessary to survival in its native habitat. The seeds are contained within flat white-yellow discs evolved to be carried by the wind. With the exception of hitching to animals and equipment, they don’t often travel more than 100 meters from the parent tree (Bertolasi 2015, 689). The seeds do not need to go through dormancy or temperature induced modifications to germinate. They need moisture to begin the process, but once started, they tolerate periods of dessication, cycles of wetting and drying, and osmotic stress. They need some warmth to germinate but are otherwise fairly tolerant of fluctuations. The seeds will germinate in the dark (Wesche 2011, 94). Seedling It is possible that U. pumila evolved a precocious seeding habit and highly flexible germination requirements because in its native habitat, a large number of seedlings succumb to herbivory (Wesche 2011, 92). The seedling stage is an important threshold. The growth of the young tree will not continue if the site is not flooded with sunlight and a level of moisture consistency is not present. A very low shoot/root ration indicates roots try and reach water as fast as possible. (Wesche 2011, 97). Dulamsuren’s research on the Mongolian steppes shows that, “The survival of very young seedlings during the first weeks after germination seems to be the bottle neck retarding the establishment of U. pumila on the slopes. Once U. pumila has passed this critical stage, the seedlings are not dependent on extreme years of high precipitation” (Dulamsuren 2009, 570). Sapling The sapling stage for U. pumila is characterized by rapid growth. Water requirements are less important at this stage, but if moisture is available, the growth rate from seedling to a small tree is astounding (Dulamsuren 2009, 571). Specific growth rate data appeared to be absent from the literature. The sapling stage is also the point beyond which hand pulling becomes out of the question. The quickly developing root system adheres firmly into the soil substrate. Tools can still be used for removal, but if the entire root is not removed, the plant will resprout and resume top growth. Mature As the tree grows into maturity it becomes increasingly hearty and drought resistant. It reaches reproductive age by 10 years (Zalapa 2010, 165). In its natural habitat, “The data suggests that U. pumila trees growing in savanna-like stands on the south-facing slopes of northern Mongolia are usually not limited by drought nor are they sensitive to photoinhibition during summer drought” (Dulamsuren 2008, 22). It responds to water shortage and dessication by shutting down part of the leaf structure. The dieback of branches reduces the level of transpiration and

Parr Field Elm Sapling ~ 4 Months from germination JBW 10/21/15

pushes the tree into a tighter form. The tree responds to longer periods of drought stress by dying back to the root crown and returning growth in a shrubbier compact form as the water availability allows. Senescent

U. pumila does not die gracefully. As branches die back, they split apart at the weak junctures with each other and at the main trunk. Despite its resistance to Dutch Elm Disease (Ophiostoma ulmi) or (DED), it is still prone to a number of insects, bacterial, and fungal diseases. A disease complex known as “wetbark” is very common both in natural stands and in introduced areas. The tree continues to be reproductively viable long after it’s prime. In the wild, under the best conditions, trees have been

known to grow upwards of 70 feet spanning over 200 years (Wesche et al 2011, 96). However, in most cases, including introductions to harsh circumstances, the trees are lucky to grow 25-50 years (Leopold 1980, 177). Water Use

U. pumila can exist in extremely dry sites, through various adaptive techniques. They prefer contact with the water table as indicated by their natural occupation of seasonal stream beds. They will not tolerate standing water however (Dulamsuren 2009, 23). The water seeking root systems grow to seek pockets of water in the soil substrate as well as widen out to take advantage of the rain that may fall. “The shallow and wide distribution of tree roots facilitated the utilization of shallow water when ground water was not available. This belowground biomass allocation strategy is common and critical for plants distributing in the semi-arid environments to collect water through vast root systems” (Li Gang 2011, 222).

These trees are evolved to withstand insecure water supplies. They do not regulate their transpiration in response to drought stress as some desert plants, but rather continue full transpiration to evaporatively cool the high leaf temperatures during the day. U. pumila instead employs the technique of altering the osmotic potential in the roots to raise the water uptake to counter the continuing water loss. (Dulamsuren 2008, 23). This immediate physiological adaptation to drought stress is aided by continued growth incorporating structural improvements to improve water use efficiency and further drought resistance. Small xylem vessels are developed to resist cavitation of the vascular system in the transport of water to the

Sibirische Ulme (Wikipedia)

leaves (Dulamsuren 2008, 23). Drought damage occurs only under severe conditions. In a study near the Aral Sea, “U. pumila exhibited reduced water use in response to the termination of irrigation water supply. As its stem and canopy growth continued, the enhanced water use efficiency of U.pumila may be an adaptation to the cessation of irrigation” (Khamzina et al. 2009, 1872).

Reproduction U. pumila relies primarily on sexual reproduction, although there are cases that call for vegetative reproduction (Wesche 2011, 97). On difficult dry sites, clonal reproduction may be more prevalent because of the lack of resource input for the energy to put into seed production (Dulamsuren 2008, 24). Most elm species are self incompatible. The seed production, although prolific under supportive conditions, is generally distributed close to the parent plant, so in order for strong levels of genetic exchange to occur, the pollen dispersal has to make up the difference (Zalapa 2009). Bertolasi et al measured pollen dispersal through paternity tests and found distances up to 7.89 kilometers from the parent tree. This potential for high pollen immigration helps to maintain the genetic connection between isolated stands of trees. The pollen dispersal rates are vastly increased under decreased forest density, thereby improving gene flow and subsequent adaptability in open landscapes (Bertolasi 2015, 690). Genetics

U. pumila shows weak barriers to cross fertilization, therefore it hybridizes readily with other elm species. (Bertolasi 2015, 689). Multiple studies show that existing genetic diversity among the introduced U. pumila is augmented by cross pollination with the native elms. It is possible that DED resistance is introgressed into native populations, but more likely that increased habitat adaptability from the expansion of genetic diversity leads to greater success. (Bertolasi 2015, 690)

In a study in the Po River region of Northern Italy, conducted by Bertolasi et al, pollen dispersal and its effects on gene flow and hybridization was studied between the introduced U. pumila and the native Ulmus minor. The natural forests of the region have been continually anthropically denuded since the Neolithic age creating an agricultural mosaic of land. The remaining native U. minor trees have been heavily affected by DED, thereby opening the niche for the DED resistant U. pumila to succeed. Paternity analysis of the gene flow between the two species may give clues to the role of genetics in determining invasive potential of U. pumila. (Bertolasi et al. 684). The researchers found clear evidence of hybridization between the native elm species and the introduced elm species in the direction of an increasing genetic component of U. pumila in the hybrids. The conservation fear is that ultimately the invasive elms will genetically overtake the native populations. Ulmus pumila clump near Yellowjacket Canyon, Co.

In another study, Zalapa et al researched the hybridization with Ulmus rubra aiding the invasion of U. pumila in the eastern and mid-western USA. (Zalapa 2009). Hybridization helps overcome the founder effect by overcoming low levels of genetic diversity in a small number of introduced individuals (Zalapa et all 2009, 157). It was determined that a higher level of genetic diversity through hybridization may contribute to the invasiveness of U. pumila in this region by conferring adaptability to a greater range of habitat conditions (Zalapa 2009, 166). Allelopathy

Allelopathy is a tool shown to be used by U. pumila to suppress competition to ensure successful establishment. This can become a characteristic that grants more potential for invasion, although the research that verifies this characteristic is still in its infancy. In a study in Madrid, Spain, Esther Perez-Corona demonstrated allelopathic effects of U. pumila leaf litter on native riparian understory species. The experiments showed that chemical compounds in the leaf litter slowed down radicle extension and shoot growth on the test species, although there was no effect on germination rates. They concluded that allelopathy is indeed a factor in U. pumila becoming invasive in riparian and riverine ecosystems, but more experiments are needed to confirm this result and explore the consequences. (Perez-Corona et al. 2013, 7) Habitat

Ulmus pumila Characteristic Citation

Native Distribution Southern Mongolia, Northeastern China, Korea, Southern Russia

Dulamsuren 2009

Introduced distribution Widely dispersed over Europe and North America

USDA Guide 2014 Leopold 1980

Habitat Preferences

Native habitat is open grasslands, steppes, floodplains, Prefers full sun. Very adaptable to difficult conditions when introduced. Thrives on disturbed soils, and lack of management.

Dulamsuren 2009 Wesche 2011

Plant Community

Tends to grow in isolated clumps. Does not normally associate with other plants. Native refugia of prehistoric forests. Allelopathic effects. Only tree species in the Gobi desert.

Perez-Corona 2013

Temperature Range 21 C to -11 C 4C Mean Wesche 2011 Precipitation Range 1750 mm to 20 mm 450mm Mean Wesche 2011

Soil types Rocky. Well drained. PH 5.5-8.0 Dulamsuren 2009

Water requirements

Does not tolerate stagnant water or poor drainage. Can adapt to drier sites with a shrubbier form. Crown dieback to conserve water resources.

Dulamsuren 2008

Native habitat The existing native habitat for U. pumila is primarily the Mongolian steppes, Gobi Desert, Northern China. Southern Siberia, and North Korea.

Natural distribution range of Ulmus pumila in hatched area over annual precipitation (Reproduced from Wesche et al 2011, 92)

U. pumila persists in its native habitat in northeast Asia. The communities tend towards sparse individuals along intermittent waterways and in scattered clumpy groves in the grasslands and steppes. This community structure probably results from a scarcity of resources and the extreme demands the habitat plays on capabilities for growth. The regions are generally semi-arid and prone to temperature extremes. The soils are of low to moderate fertility, and much of the steppe country is prone to high winds. With these limitations to growth, U. pumila naturally chooses the most promising sites for survival. It prefers sun exposed sites in mountainous regions and floodplains of the forest-steppe ecosystems. (Wesche 2011). “Such U. pumila stands on south-facing slopes are not forests in the strict sense, but are structured like savannas consisting of small numbers of trees scattered over the grasslands” (Dulamsuren 2009, 563). It will grow in many types of soil textures, but does best in rocky soils that create spaces for water pockets to form. It is the only tree species growing in some parts of the Gobi Desert (Wesche 2011, 92).

Current stands of native Siberian Elm in Mongolia have been proposed to be remnants of much larger stands. The pollen cores do not verify this, but it is noted that the areas in which they grow are not ideal for pollen preservation. There are theories that the existing stands are possibly refugia from an antiquated forest but the evidence hasn’t yet been found to support this (Wesche 2011, 98). Perhaps the current climate of the region doesn’t support the dense growth of U. pumila, but as noted, the genetics of this species support physiological and structural adaptations towards perseverance under the most difficult conditions.

When conditions are improved, even slightly, as they are introduced to the harsher environs of other regions of the world, the inherent biology of the species proves more than adequate for success. In the words of an early proponent for their introduction to the U.S., Mr. Frank Nicholas Meyer, using the original common name ‘Chinese Elm’, writes, “The Chinese elm (Ulmus pumila), used all over northern China and Manchuria as an avenue, shade, and timber tree, resists droughts, extremes of heat and cold, and neglect remarkably well; will be a good shade tree for the semi-arid Northern regions of the U.S.” (Webb 1948, 274).

Ulmus pumila 'Pendula' photographed by Mr. Frank Nicholas Meyer on an old grave near Fengtai, Chihli, China. March 27th 1908. The timing and the authorship of this photograph opens the possibility that this very tree may have provided genetic stock for one of the several introductions to the U.S.

Introduction to new habitat Although U. pumila was first introduced to Europe in the 16th century (Bertolasi et al 2015, 684), it didn’t officially make it to the Americas until the early 20th century. The first verifiable records of its introduction to the U. S. were in 1905 by J.G. Jack of the Arnold Arboretum of Harvard University. Seeds were collected from the Temple of Pekin and along with cuttings, were shipped by Frank Nicholas Meyer in 1908, and propagated out by the UC Berkeley Forest Nursery in 1917 (Leopold 1980, 175). People were very excited about its introduction, and its further propagation and dispersal were met with a beckoning landscape. “Because of Siberian Elm’s fast growth and tolerance to almost any site, nurserymen raved about this species and consequently through their zealous promotion were responsible for its immediate popularity and tremendous success” (Leopold 1980, 175). In the 1930’s Governor Tingley of NM offered U. pumila seedling for free to anyone who promised to plant them. He was trying to create a tree canopy on a barren landscape in New Mexico’s urban areas. By 1948, in the Great Plains area of the U.S., U. pumila became the primary tree used for windbreaks and represented 75% of the new street, shade, and park plantings (Webb 1948, 274).

The reasons behind its introduction and ultimate wide ranging dispersal were numerous. It showed promise to vegetate and maintain areas where taller trees and shrubs were naturally scarce. (Wesche 2011). U. pumila was bred as a solution to create Mid-western windbreaks and soon presented itself as a fast growing and hearty street and shade tree. It was publicized to the Midwest as a shelterbelt tree because it could withstand the wind and hold the soil in place, and to the Southwest states because of its resistance to drought, and tolerance of low soil fertility, (Leopold 1980). The fact that it was resistant to DED also conferred a great deal of trust in the viability of this tree to fill the holes left by the fallen Ulmus americana (American Elm) and Ulmus rubra (slippery elm). It was a tree that provided solutions to a growing and increasingly urbanized population expanding into more vegetation challenged terrain.

Similar to the willing and hopeful introductions of many other species that ultimately became invasive, it was praised for its short-term benefits and ease of adaptability without considering the long-term peril of its success. The enthusiasm of its introduction is clearly spurned by it’s adaptive capabilities and the impatience for the establishment of landscape trees for shelterbelts and urban canopies. It has since found many open niches beyond those intentionally provided, and integrated itself into multiple wild habitats, landscaped ecosystems, and into a great number of American communities. Fragmentation

With the pressure of its persistent introduction to the landscape, the invasion was also assisted by the dynamics of landscape fragmentation. As noted earlier, habitat fragmentation and anthropic alterations of the environment can increase gene flow partly through increased pollen dispersal. (Bertolasi et al 2015, 683). This creates even greater genetic diversity in the U. pumila populations which gives it more tools for adaptation to difficult environments. Since U. pumila also shows the ruderal characteristics of early succession species, it is very at home in highly disturbed environments associated with anthropic effects on the landscape. Fragmentation may disrupt the evolved ecological balance of native species in a landscape, but to U. pumila, nothing could be more encouraging.

Extent of invasion in North America U. pumila is now present in nearly every state in the U.S and is include on invasive species lists in 25 states (Weeds U.S. Database). It will likely only live 25-50 years in its introduced habitat, but It may be the most planted of any introduced tree species in the U.S. (Leopold 1980, 178). It has hybridized with native populations of U. rubra and U. americana and has made a place for itself in farmer’s fields, along streets and homeowners yards, in riparian areas, in parks, in vacant lots, abandoned buildings, and in cracks in sidewalks. It not only replaces existing native biota through sunlight restricting competition and resource manipulation, but it has created novel niches to grow in places where nothing has grown before. It has been enthusiastically asked to help improve and expand human habitat, but arguably, it has created more problems than it has solved. Problems with pumila

U. pumila grows very quickly into forms structurally unsound for its size. It develops low branch attachment angles that are structurally weak and prone to breakage in storms. It’s habit of shutting down portions of its crown in response to drought stress causes large amounts of dead material. This isn’t a problem in the wild, but in an urban setting, this can be a liability. Its prolific seeding habit creates numerous enemies and overwhelms the native species. In Albuquerque, NM the spring seeding frenzy is known as “Tingley Snow” after the controversial governor who emphatically led its introduction to the state. This seeding event is perfectly timed for the summer rains promising fields of viable seedling that under the right conditions dominate the landscape. These ‘urban wild’ forests thrive on lack of management and create green enclaves out of forgotten pieces of land. Attempts to control the invasion are thwarted unless they are maintained diligently over a span of years. Despite marks against this misplaced species, it has found a home in North America, and for better or worse is likely here to stay.

Integration into human communities U. pumila still provides ecosystem services and tolerates the anthropic ill-treatment of the landscape. In some areas, similar to its native Gobi Desert, it is virtually the only tree that can survive to provide shade, some measure of energy benefits, storm-water mitigation, erosion control, and aesthetic pleasure to an otherwise barren street. The proposition of its removal presents a predicament. It is too integrated into the lives of people and in the ecology of communities to simply remove it without considering the ramifications. Each case needs to be considered carefully. Fortunately, there are some alternatives, given the time and perseverance to enact them.

Distribution Map for Ulmus Pumila (Plants Database)

Management

Mapping The first step in managing the existing U. pumila populations is to understand the extent of its presence the and severity of its influence. As previously stressed, there may be cases for its desired inclusion in certain landscape applications. Regardless, it is important to map the presence of U. pumila in the landscape. Typically, the mapping of trees involves geo-referencing the individuals and stands, measuring the diameter at breast height (DBH), assessing their overall structure and condition, and assembling this information to GIS mapping software. This information can be used to assess the ability of a community or agency to make management priorities. However, U. pumila presents certain species specific problems to being mapped. Their tendency towards multi-trunk forms, and dying back to a shrubby form makes their counting more difficult than single trunk specimens. The tendency to grow in thickets of small diameter individuals suggests that they should be mapped following mapping standards for areas of infestation rather than as individual trees. Maintenance

With a sense of the localized presence of U. pumila in a region, decisions can be made as to how to manage them. Since U. pumila thrives on low maintained areas, the more resources for maintenance, the higher success rate. However, management resources are often in short supply to adequately contend with its presence. Additionally, U. pumila is still providing benefits in many cases so that a sudden comprehensive removal plan would not be in the best interest of the either the landscape or the community. So the decisions need to consider temporal, spatial, and management resource factors. The maintenance and control of U. pumila will require long-term planning and an extended input of management resources. The ultimate goal may not be to remove every U. pumila tree, but rather to remove them from certain sites and generally slow down their spread. Either way they need to be managed to keep their presence from displacing native biota. Replacement Ideally, the most promising way to manage U. pumila is through a sequenced replacement and removal plan. This is most applicable in deliberately landscaped sites. Another tree species can be planted underneath the one to be removed with the plan to let it establish before the invasive one will be removed. Care needs to be taken in herbicide use in this situation. Regional recommendations for suitable species for replacement are available for all but the most difficult sites. These replacement trees should be chosen from a wide range of genus and species to ensure the maintenance of biodiversity in landscape plantings. There are also alternative non-invasive Asian elm species that share the same characteristic of DED resistance. Interestingly, some of these alternatives were available early in the introduction period, but the predictive capabilities for invasion potential of U. pumila were underdeveloped and the alternate species weren’t seriously considered.

In the early 20th century, Frank Nicholas Meyer sent cuttings from another Asian elm species, Ulmus parvifolia (Lacebark elm). It was not deemed quite as hearty as U. pumila and therefore wasn’t taken as the best option for difficult site conditions. However, in retrospect, it may have proven not only suitable, but in most cases preferable. Fortunately, it is still being bred, and will provide a suitable alternative in most cases. U. parvifolia seeds in the fall, limiting its dispersal abilities and develops a much stronger structure with more useful wood production. Breeding programs at the Morton Arboretum are currently hybridizing varieties of U. parvifolia to provide a host of ulmus alternatives to pumila.

Ulmus parvifolia Ulmus pumila

There is some confusion in the common names that would need to be resolved before recommendations towards another Asian elm species would be accepted by the public. Early on, both species were called Chinese elm creating a muddled connection between the negative characteristics and the wrong species. U. pumila at first, was planted almost exclusively under the name ‘Chinese elm’. Later, an attempt to change the name to ‘Siberian elm’ was applied to emphasize the greater cold tolerant characteristics of U. pumila, but by that time, the common name ‘Chinese elm’ had mostly stuck. The ‘good’ Ulmus, unfortunately was also called ‘Chinese elm’ (U. parvifolia). An attempt to rename it, ‘Lacebark elm’ to alleviate the confusion has not completely caught on. The common name confusion is easily rectified by using the Latin names, but the public won’t likely participate. When the words ‘Chinese Elm’ are spoken, most people still visualize ‘U. pumila’. This obstacle will need to be removed before an adequate replacement program can be initiated. Fortunately, the physical and functional differences between the two trees are absolutely clear. “Chinese [parvifolia] elm is an asset to the urban environment and not the liability that Siberian [pumila] elm frequently becomes” (Leopold 1980, 178).

Mitigation and Removal

Site Physical Methods Cultural Methods Chemical Methods Citation

Roadsides, irrigation ditches, fence lines, or noncrop areas

Seedlings (< 3/8" diam.) and saplings (3/8" to 2.5" diam.): dig or grub with shovel, hoe or weed tool. Remove as much root as possible. Burning may work for seedlings, but anything larger resprouts after top is killed off.

Train road crews to identify and report infestations along roads; implement requirements for vehicle operations.

Light infestations: for trunks < 3' diam. and less than 8' tall, use basal bark treatment; for trunks > 3" diam., girdle or use cut- stump with herbicide.

USDA Field Guide 2014

Small trees (2–3" diam.): remove individual plants using the cut/stump method.

Use weed screens on irrigation canals.

Dense infestations: use foliar application with backpack sprayer; truck/ATV- mounted sprayer.

Larger trees (> 3" diam.): girdle trunks and leave in place or use cut-stump method. Where access is not limiting, remove trees with an excavator or backhoe. Anticipate the need to control resprouts.

Wash under vehicle after application to prevent spread.

Urban and developed areas. Parks, yards, sidewalk cutouts.

Same as above, but the choice to girdle and leave the tree standing may not always be appropriate for the safety and aesthetic consideration of the site. In that case, the repeated cutting or cut/stump method may be preferable.

Educate to prevent the continued sale in nurseries and planting in the landscape. Map the extent of the infestation. If possible, prior to removal, replant with appropriate species. Once established, remove pumila. Clean up after seeding events.

Same as above, except take particular care when using herbicide around people, pets, and in landscaped areas.

Leopold 1980 Radosevich 2007

Rangelands, pastures, or riparian corridors

Light infestations: use an individual plant method to remove trees.

Reseed with certified, weed-free seed; fertilize and irrigate, if possible, to make desirable plants more competitive.

Check with state environment departments for appropriate and legal application for herbicide use. For light infestations with Siberian elm interspersed with desirable native plants, use a backpack sprayer to treat individual plants (basal bark, cut-stump, or girdle with herbicide).

USDA Field Guide 2014

Dense infestations: remove stems with heavy machinery in the winter; followup with chemical treatment to control resprouts in late summer.

For dense infestations in disturbed areas with few desirable plant species present, use broadcast spraying.

Wilderness, other natural areas, and/ or small infestations

Same as above. After passing through infested areas, inspect and remove seed from animals, clothing, and vehicles before entering treated or uninfested areas.

Same as above. USDA Field Guide 2014

(Management Options Table adapted from USDA Field Guide for Managing Siberian Elm in the Southwest 2014)

Removal Techniques Detail Cutting - Cut the tree as close to the ground as possible. The resprouts will need to be periodically recut. This pattern may continue for several years. Excavating the root system - The root system is removed with shovels or heavy machinery. It will be necessary to remove it all because chunks of root still left in the ground will resprout. Fire - This is only recommended for seedlings. Anything larger than a seedling will resprout after the top dies back Girdling - In the late spring to mid-summer, remove a 3” strip of bark from the circumference of the tree without damaging the xylem tissue. Leave the tree standing until the top is dead. May be combined with herbicide application for faster results. Herbicide - Foliar herbicide is appropriate for smaller trees under 8’ applied after the leaves are fully expanded. Triclopyr is recommended. Basal bark spraying may be used on intermediate trees from 2-3” in diameter in midwinter or late summer. Triclopyr mixed with penetrating oil is recommended. Cut-stump method with herbicide - The best time is in the fall. Cut the tree low to the ground and within 5 to 15 minutes, treat the stump with a paintbrush, wick applicator, or low-volume sprayer. Glyphosate is recommended diluted to 20%. Girdling with herbicide - Girdle the tree as described above and coat the girdled area with glyphosate or triclopyr. (USDA SW Field Guide 2014, 3-4) Conclusion Despite its invasive potential, U. pumila may still be a reasonable option for many landscaping demands. Regardless of its present use, It has integrated itself into many North American communities, and therefore requires perpetual management to contain its spreading. Proactive communities with the knowledge, foresight, and management resources, may be able to implement a replacement and removal plan, but this is likely more the exception than the rule. Either way, knowing the biological potential for invasiveness, the ecological problems created, and the techniques that may implemented for control, may help its persistent existence remain tolerable and manageable. Without actively addressing the spread of this extremely hearty and adaptable tree in particular areas, it will continue to excel regardless of our opinion towards it presence.

References Bertolasi B. et al. 2015. “A last stand in the Po Valley: genetic structure and gene flow patterns in Ulmus minor and U. pumila” Annals of Botany. 115: 683-692. Brunet et al. 2013. “Hybridization and introgression between the exotic Siberian elm, Ulmus pumila, and the native Field elm, U. Minor, in Italy.” Biological Invasions. 15: 2717-2730. “Conservation Plant Characteristics for Ulmus pumila (Siberian Elm)” USDA. Natural Resources Conservation Service. Distribution Map for Ulmus pumila. Plants Data Base. Web download. 3/13/16. https://www.usanpn.org/nn/Ulmus_pumila Dulamsuren, Choimaa, et al. 2009. “Performance of Siberian elm (Ulmus pumila) on steppe slopes of the northern Mongolian mountain taiga: Drought stress and herbivory in mature trees.” Environmental and Experimental Botany. 66: 18-24. Dulamsuren, Choimaa. et al. 2009. “Establishment of Ulmus pumila seedlings on steppe slopes of the northern Mongolia mountain taiga.” Acta Oecologica. 35: 563-572. “Field Guide for Managing Siberian Elm in the Southwest.” 2014. USDA Forest Service. Foresry Forum. http://www.forestryforum.com/board/index.php?topic=72813.20. Web Accessed 3/13/16. Khamzina, A., J.P.A> Lamers, and P.L.G. Vlek. 2008. “Tree establishment under deficit irrigation on degraded agricultural land in the lower Amu Darya River region, Aral Sea Basin” Forest Ecology and Management. 255: 168-178. Khamzina, A. et al. 2009. “Transpiration and early growth of tree plantations established on degraded cropland over shallow saline groundwater table in northwest Uzbekistan” Agriculture and Forest Meteorology. 149: 1865-1874. Leopold, Donald J. 1980. “Chinese and Siberian Elms”. Journal of Arboriculture. 6(7): 175-179. Li gang et al. 2011. “Biomass carbon storage and net primary production in different habitats of Hunshandake Sandland, China” Acta Ecologica Sinica. 31: 217-224. McIlvain, E. H. and C. G. Armstrong. 1965. “Siberian Elm: A Tough New Invader of Grasslands”. Weeds. 13(3): 278-279. Moore, Lincoln M. “Plant Guide: Siberian Elm” USDA. NRCS. ed. 2003.

Moore, Lincoln M. “Plant Fact Sheet: Siberian Elm” USDA. NRCS. ed. 2006. Perez-Corona, Esther M. et al. 2013. “Allelopathic potential of invasive Ulmus pumila on understory plant species.” Allelopathy Journal. 32: 101-112. Radosevich, Steven R., Jodies S. Holt, and Claudio M. Ghersa. 2007. Ecology of Weeds and Invasive Plants. Hoboken, New Jersey: John Wiley and Sons. Sibirische Ulme. Wikipedia auf Deutsch. Web download. 3/14/16. Virgina Tech Images. http://dendro.cnre.vt.edu/dendrology/syllabus/factsheet.cfm?ID=134 Webb, Walter E. 1948. “A report on Ulmus pumila in the Great Plains Region of the United States” Journal of Forestry. 274- 278. Weeds U.S. Database. Web download. 3/13/16. http://www.nps.gov/plants/alien/fact/ulpu1.htm Wesche, Karsten et al. 2011. “Trees in the desert: reproduction and genetic structure of fragmented Ulmus pumila forests in Mongolian drylands” Flora. 206: 91-99. Wikipedia. “Ulmus pumila in Gobi desert” https://en.wikipedia.org/wiki/Ulmus_pumila Accessed: 3/13/16. Yellowjacket Canyon. Southwest Colorado Wildflowers. Web download. http://www.swcoloradowildflowers.com/Tree%20Enlarged%20Photo%20Pages/ulmus%20pumila.htm Zalapa, Juan E., Johanne Brunet, and Raymond P. Guries. 2010. “The extent of hybridization and its impact on the genetic diversity and population structure of an invasive tree, Ulmus pumila (Ulmaceae).” Evolutionary Applications. Blackwell Publishing. 3: 157-168.