Montana Field Guide

PLANTS: A small, shallowly rooted, deciduous tree that grows to 12 m tall and 50 cm in diameter. Trees have an open crown and spreading branches. Sources: McGregor et al. 1986; Lesica et al. 2012; Lesica and Marlow 2013.

BARK: Dark gray and shallowly furrowed. Source: Lesica et al. 2012.

BRANCHES / BUDS: Twigs are green to brown and glabrous to densely pubescent. The terminal bud is reddish-brown to nearly black and acute to acuminate, while the lateral buds are rounded and in pairs. Lenticels are prominent. Sources: McGregor et al. 1986; Lesica et al. 2012; Lesica and Marlow 2013. Morris et al. 1962.

LEAVES: The odd-pinnate leaves are oppositely arranged, petiolate, ovate in outline, with 5 to 7 leaflets. The entire leaf is 11-30 cm long by 8-18 cm wide. The leaflets have short petioles that are lanceolate in shape with serrate margins, 5–12 cm long, and glabrous to silky-pubescent below. Sources: McGregor et al. 1986; Lesica et al. 2012.

INFLORESCENCE: Small inconspicuous flowers arise from a panicle which appears before the leaves. Green Ash is a dioecious plant, with male and female flowers found on separate trees. The calyx is 1–1.5 mm long and cup-like with 4 shallow lobes. The corolla is absent. Male flowers have 2 stamens that are 2–4 mm long. Female flowers have 2 aborted stamens and 1 pistil with a superior ovary that has a 2-lobed stigma.

In eastern Montana, flowers are produced as the leaves expand, commonly in late May (Lesica and Marlow 2013). Fruits mature in late summer but may remain on the tree through the winter.

Green Ash is a deciduous tree with a dominant single stem (trunk) and opposite pinnately compound leaves having 5-7 leaflets.
Maples (Acer spp.) also have a dominant single trunk and opposite leaves; however, leaves are either single and lobed or have three leaflets, that are each lobed. Sources: McGregor et al. 1986; Lesica et al. 2012.

Green Ash – Fraxinus pennsylvanica
*Deciduous tree up to 12 meters tall with a single main stem (trunk).
*Leaves are oppositely arranged, pinnately compound with 5 to 7 leaflets, that are lanceolate to elliptical in outline. Leaflet margins are serrate, and glabrous to silky-pubescent below.
*Twigs are green to brown and glabrous to densely pubescent.
*Terminal bud is reddish-brown to nearly black and acute to acuminate, while the lateral buds are rounded and in pairs. Leaf scar is raised, hemispheric, bundle traces numerous, continuous in a curving line.
*Bark is ashy gray to brown in color, with interlacing corky ridges forming obvious diamonds; older trees may be somewhat scaly.
*Fruit is a single 1-seeded samara.

Box-elder - Acer negundo
*Dioecious tree to 15 meters with one to multiple stems (trunks).
*Leaves are oppositely arranged, pinnately compound with 3 to 5 leaflets, lanceolate to ovate in outline. Leaflet margins are coarsely serrate or somewhat lobed, and veins are pubescent.
*Twigs are green to purplish green, glabrate to pilose, leaf scars narrow, meeting in raised points, often covered with a glaucous bloom.
*Buds are white and hairy, lateral buds appressed.
*Bark is thin, gray to light brown, with shallow interlacing ridges; young bark is generally warty.
*Fruit is a double 1-seeded samara.

TAXONOMY
Montana's plants are sometimes considered to be var. lanceolata or var. subintegerrimus, but these varieties are now considered of little taxonomic value (McGregor et al. 1986).

In Montana, Green Ash occurs in the Plains zone (Lesica et al. 2012). Trees grow in alluvial soils along rivers, streams, and ephemeral drainages and on cool north-facing slopes. In the Great Plains the species is hardy, tolerating climatic extremes and occurring in two distinct habitats: drier woody draws and riparian areas. It can grow on a range of soils from clay substrates that are often subject to frequent flooding to sandy or silty soils that may be limited in moisture (Kennedy 1990). Green Ash woodlands are most abundant where topography is broken, such as drainage divides or along incised stream beds. These draws are more mesic than surrounding uplands because they accumulate and retain snow (Lesica and Marlow 2013).

Refer also to the Great Plains Wooded Draw and Ravine Ecological System

ASSOCIATED VEGETATION
Green Ash is the dominant and often only deciduous tree found in woody draws of eastern Montana (Lesica and Marlow 2013). American Elm (Ulmus americana) is found in some stands and occasionally is co-dominant. Box-elder (Acer negundo) also occurs in some stands but it is never abundant.

Understory vegetation of Green Ash woodlands is rich in shrub and herbaceous species. Chokecherry (Prunus virginiana) and Western Snowberry (Symphoricarpos occidentalis) are dominant shrubs, with American Plum (Prunus americana), Pin Cherry (Prunus pensylvanica), Western Poison-ivy (Toxicodendron rydbergii), Serviceberry (Amelanchier alnifolia), Succulent Hawthorn (Crataegus macrantha), and Wood’s Rose (Rosa woodsii) being common in many stands. Dominant graminoids in Green Ash stands are Sprengel’s Sedge (Carex sprengelii) and many introduced grasses including Kentucky Bluegrass (Poa pratensis), Smooth Brome (Bromus inermis), Japanese Brome (Bromus japonicus), and Quackgrass (Agropyron repens). Common native broad-leaved plants include Virginia Strawberry (Fragaria virginiana), Canada Violet (Viola canadensis), Northern Bedstraw (Galium boreale), Maryland Black Snakeroot (Sanicula marilandica), Kidneyleaf Buttercup (Ranunculus abortivus), Cleavers (Galium aparine), Starry Solomon’s Plume (Smilacina stellata), and Purple Meadowrue (Thalictrum dasycarpum). Common introduced forbs are Common Dandelion (Taraxacum officinale) and Common Burdock (Arctium minus).

Heavy Sedge (Carex gravida) is a Montana Species of Concern and known from only a handful of Green Ash woodland sites in eastern Montana (Lesica 2001; Lesica and Marlow 2013).

ENVIROMENTAL SITE CHARACTERISTICS [Adapted from Lesica and Marlow 2013]
* Flowers and young fruits are very sensitive to late spring frosts (Wright 1959).
* Tree seedlings grow equally well in sun or shade (Borger and Kozlowski 1972). They are intolerant to saline soil conditions (Pezeshki and Chambers 1986). Seedlings can survive for 1-2 years when growing in dense herbaceous cover, but their growth is reduced because of competition with soil moisture (Lesica and Marlow 2013). Dormancy occurs earlier for drought-stressed seedlings than for those that are well-watered (Shumway et al. 1991).
* Tree seedling recruitment was higher in closed understories of mesic sites that had less grazing (Lesica 2001). Woodlands with more closed canopies have extensive leaf litter on the ground with more native forbs and relatively less cover of grass-like plants. Dense grass cover appears to inhibit seed germination (Lesica 2009).

FIRE [Adapted from Lesica and Marlow 2013]
The role of fire in Green Ash communities is not well studied. Woody draws where Green Ash grow are in shaded ravines which may be more protected from fire. It is possible these draws may serve as a natural fuel break. The species is a prolific re-sprouter which suggests it is fire adapted. Controlled spring burns in western South Dakota and wildfires in eastern Montana both increased sprouting. However, sprouting was less where fires did not reduce introduced sod-forming grasses. Although Green Ash re-sprouts readily, intense fire may destroy plants and sites may temporarily revert to shrublands. Fire frequency is thought to have declined with European Settlement.

PATHOGEN [Adapted from Lesica and Marlow 2013]
Green Ash is highly susceptible to the white stringy heartrot fungus (Perenniporia fraxinophila; Fomes fraxinophilus) in the northwestern portion of its range. This native and common heartrot rarely kills its host tree but can weaken infected trunks and branches. Infected trees become more susceptible to breakage by wind or ice, and older or larger trees are more vulnerable. Affected tree stumps can re-sprout producing multiple stemmed trees.

ANIMAL INTERACTIONS [Adapted from Lesica and Marlow 2013]

Ungulates: Green Ash woodlands provide important summer and winter range for Mule Deer (Odocoileus hemionus) and are crucial wintering habitat for White-tailed Deer (Odocoileus viginianus). Green Ash woodlands provide important escape cover, travel corridors, late summer and winter forage, and fawning grounds for both White-tailed Deer and Mule Deer (Swenson 1981).

Non-game Mammals: Green Ash woodlands provide important habitat for Coyotes (Canus latrans), weasel (Mustella spp.), red fox (Vulpes vulpes), Bobcat (Lynx rufus), and Meadow Voles (Microtus pennsylvanicus).

Game Birds: During the fall and winter months Green Ash woodlands provide important habitat for Sharp-tailed Grouse, particularly when snow makes grain fields inaccessible. Wild Turkeys commonly use Green Ash woodlands.

Non-game Birds: Green Ash woodlands are important for many species of birds that would otherwise not occur in the semi-arid Great Plains including many songbirds typical of eastern deciduous forests. Several species of raptors use Green Ash woodland canopies for nesting. These include Great Horned Owl, Long-eared Owl, Swainson’s Hawk, Red-tailed Hawk, Ferruginous Hawk, Sharp-shinned Hawk, Eastern Screech Owl and American Kestrel. Yellow-billed Cuckoo, Downy Woodpecker, and Red-eyed Vireo may also be found nesting in the canopy. Black-billed Cuckoo, Gray Catbird, and Warbling Vireo require tall shrubs, and the Ovenbird requires dense ground cover and leaf litter. At least ten bird species of conservation concern commonly occur in Green Ash woodlands.

Trees reproduce by seed and by sprouting from a stump. The persistence of Green Ash Woodlands (woody draws) is dependent upon both seed production/germination and stump sprouting (Lesica 2001).

FRUITS
The fruit is a samara. Samaras are borne in clusters; each being elongated, winged, and single seeded (Kennedy 1990, Lesica 2001).

LIFE CYCLE
Cold stratification is required for seeds to germinate (Lesica and Marlow 2013).
Flowers are produced as the leaves expand, usually in late May for eastern Montana. Seedlings grow equally well in sun or shade (Borger and Kozlowski 1972).
Stems (trunks) rarely persist for more than 100 years on the Northern Great Plains.
Seeds are wind dispersed short distances from the parent tree (Kennedy 1990, Lesica 2001).
Green Ash is reported to have a short-lived seed bank (Farrar 1995). However, harvested seeds can remain viable for at least one year if stored properly at room temperature (Fowells 1965).

ECONOMICS OF RECREATON
Woodlands provide important habitat for deer, attracting a lucrative hunting recreational economy. Turkey hunting in woodlands also contributes to the local economy.

Fur trapping was once important in these woodlands; however, as an industry it has been in decline.

A comprehensive discussion of Green Ash Woodland management and restoration can be found in Lesica and Marlow 2013, as well as in the Great Plains Wooded Draw and Ravine Ecological System profile to learn more about 'woody draws'.

PLANTINGS
Historic records reveal that Green Ash woodlands were common prior to European settlement. Green Ash was commonly planted in shelterbelts in the Great Plains and extensively cut for firewood (Peattie 1953).

Green Ash trees are commonly grown and sold by nurseries throughout Montana. The Montana Department of Natural Resources and Conservation (MT DNRC) is developing guidance on planting trees in urban settings. Green Ash is a good choice for planting at certain sites, such as along the highline in eastern Montana because it can tolerate arid and windy conditions. Green Ash is not the best choice for planting into city boulevards because they require more space, frequent pruning, and are susceptible to certain fungal rots.

WOODCUTTING
A large influx of homesteaders settled in eastern Montana during the years of 1900–1918 (Lesica 2001). Wood was needed for building houses, barns, and fences. Pine was preferred, but where pine was scarce, Green Ash could be used. This use declined in the 1920s during the Great Depression. As a result, a peak in Green Ash recruitment occurred in the 15-year period from 1926 to 1940. This surge in ash stem recruitment was likely caused from sprouting after trees were cut, and later by land abandoned in response to drought. Presently woodcutting of Green Ash is minimal.

GRAZING CONTROLS [Adapted from Lesica and Marlow 2013]
Livestock grazing and wildlife use have been implicated as the primary causes of Green Ash Woodland decline. Grazing animals congregate in these shady habitats during the hot, dry summer and early fall. However, the current condition of Green Ash woodlands may be more a reflection of the intense grazing pressure from the homestead era (1870-1930) than the post-depression era (after 1940). Cattle and sheep were common up until the 1930s when the number of sheep began to decline and the number of cattle increased. Although grazing pressures are relatively less in the post-depression era, the small shady Green Ash woodlands are often disproportionately grazed, even at moderate stocking rates (Severson and Boldt 1978). Overgrazing has a number of adverse effects on the structure of woodlands that are well documented elsewhere. The effects of different grazing systems to help retain Green Ash Woodlands have not been well studied, resulting in a lack of best grazing practices for Green Ash.

White-tailed Deer populations have increased since the homestead era in eastern Montana. White-tailed Deer use Green Ash woodlands intensively, especially in winter, and browse heavily on Green Ash likely preventing growth of seedlings and vegetative sprouts into mature trees (Swenson 1981).

Although overgrazing by livestock may be the primary agent initiating woodland decline, discontinuing livestock grazing alone is likely not enough to enhance tree recruitment. Where present, sod-forming exotic grasses must also be controlled because they directly compete and reduce seedling survival. Large, native deer populations that naturally rely on these woodlands can also hinder tree seedling growth when disproportionately used.

INVASIVE PLANTS
A number of invasive, rhizomatous sod grasses, particularly Smooth Brome, Kentucky Bluegrass, and Quackgrass, and other exotic grasses, such as Crested Wheatgrass, were introduced into the Great Plains with European settlement and have increased in rangelands under the influence of heavy livestock grazing. Lesica (2001) found a decline in tree seedling density was associated with a change in the understory from the native Sprengel’s sedge to these exotic rhizomatous grasses; this change was likely triggered by livestock grazing. Treating exotic sod grasses with an herbicide in these degraded hardwood draws resulted in an increase in Green Ash and chokecherry seedling recruitment and survival. These studies indicate that tree recruitment from seed is curtailed as the ground layer becomes dominated by a sod of exotic grasses.

Green Ash recruitment is also reported to be reduced by competition in other habitats. Lesica and Miles (2001) concluded that Russian Olive may replace Green Ash in riparian forest stands as it can grow at nearly three times the rate of Green Ash. Also, Russian Olive will establish with increasing frequency in riparian forests in eastern Montana, especially in areas where seasonal flooding no longer occurs.

RESTORATION
Fire has been a suggested process that could facilitate regeneration of woodlands on the Great Plains, but there is limited evidence to support this idea.

Where sod-forming exotic grasses are prevalent, applying an herbicide (glyphosate) to the grass has shown to greatly increase Green Ash seedling recruitment compared to untreated sod; however, surviving seedlings grew poorly (Lesica 2009).

Restoration may prove challenging in Montana as the species is at the arid limit of its range, and in current times is growing in a potentially drying warming climate.

Recruitment of Green Ash seedlings might be possible by first establishing a chokecherry understory to act as “nurse plants.” The shading provided by a healthy shrub layer reduces the vigor of sod-forming exotic grasses, which means trees seedlings will grow better. Seedlings are tolerant of shade.

EXISTING THREATS
Numerous studies have found that since 1978 the majority of Green Ash Woodlands have declined throughout Northern Great Plains (Lesica and Marlow 2013). The potential causes are many and may act independently or synergistically, as well as, differ in their importance depending upon the location and environment within the plains:

Livestock and Native Ungulate Grazing: Grazing animals often congregate in Green Ash woodlands which provide shade, succulent forage, relief from biting insects, and sometimes water. Disproportionate grazing, even at moderate stocking rates, directly and indirectly adversely affects the structure of these woodlands (Lesica and Marlow 2013). Native and domesticated ungulates forage on tree seedlings, directly removing recruitment. Rubbing and trampling can reduce tree cover. Over-use compacts soil which creates gullies and reduces infiltration to the water table. Continuous grazing pressures can raise soil temperatures and increase evaporation rates.

Invasive Plants: Invasive grasses, particularly Crested Wheatgrass, Smooth Brome, Kentucky Bluegrass, and Quackgrass, grow densely and compete for soil moisture, reducing or preventing Green Ash seed germination and tree seedling growth and survivorship. Establishment of Russian Olive trees can out-complete Green Ash in riparian forest stands of eastern Montana, especially in areas where seasonal flooding no longer occurs.

Climate Change: With possible lower levels of precipitation on the Great Plains, Lesica and Marlow (2013) hypothesized that recruitment of Green Ash could decline as the species is already at the arid edge of the tree’s geographic range.

POTENTIAL THREAT
Emerald Ash Borer (Agrilus planipennis): This metallic wood-boring beetle is native to China (Persad 2016). It was first detected in North America (Michigan) in 2002 and has since spread to at least 35 states and 5 Canadian provinces; this includes the neighboring state of South Dakota (Persad 2016; Emerald Ash Borer Information Network). This exotic beetle feeds on native and cultivated ash (Fraxinus species) trees in urban and wildland landscapes, which eventually will kill the tree. As of 2021, Emerald Ash Borer has not been documented in Montana. However, with its high potential to invade Montana, proactive efforts are being conducted by the Montana Invasive Species Council with cooperation from the Montana Department of Agriculture, Montana Department of Natural Resources and Conservation, and other agencies.

Signs of an infestation:
Infested ash trees exhibit canopy thinning and yellowing leaves, D-shaped holes in the bark, and canopy and bark loss. Infested trees tend to have branch fractures within the upper canopy, specifically located closer to the union of the trunk and the upper stems. These broken stems near the top of the canopy can be hard to see from the ground. Cracks in the bark cracks around the first branch are often present. Early detection is difficult as trees may be infested for more than 2 years before showing signs of infestation - often this is too late for treatments to be effective. Small trees may die within 1-2 years while large trees can be killed in 3-4 years. Healthy as well as stressed trees may be affected. There is some evidence that tree genotype may influence vulnerability to infestation due to host defense responses (Koch et al. 2015; Koch et al. 2020).

Dispersal Pathways:
Emerald Ash Borer adults and larvae can be transported long distances in firewood collected from infested forests. It is recommended that firewood not be transported across state lines, and particularly that firewood not be brought into Montana. Should Emerald Ash Borer establish in Montana, the ecological and economic impacts to Green Ash would be devastating.

Preventing Emerald Ash Borer:
The Montana Department of Agriculture has established a quarantine to minimize the 'risk of introduction' of Emerald Ash Borer into Montana. Potential sightings should be reported immediately to the State Quarantine Specialist and if possible, collect a sample and preserve it in rubbing alcohol for verification.

Carson Thomas, Nursery/Quarantine Specialist, 302 North Roberts Street, Helena, Montana 59601; 406-444-3428; carson.thomas@mt.gov

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