Montana Field Guide

This system is typically associated with highly intermittent or ephemeral streams. It may occur on steep northern slopes or within canyon bottoms where soil moisture and topography produce higher moisture levels than are common throughout most of the area. In some areas of the western Great Plains, in higher elevation draws and ravines, Rocky Mountain juniper (Juniperus scopulorum) can dominate the canopy. Aspen (Populus tremuloides), paper birch (Betula papyrifera), or boxelder maple (Acer negundo) are commonly present in portions of the northwestern Great Plains. In central and eastern Montana, green ash (Fraxinus pennsylvanicus) or chokecherry (Prunus virginiana) are the usual dominants. Douglas hawthorne (Crataegus douglasii) is occasionally seen as a dominant in south-central Montana, especially around the Pryor Mountains. This system is found in ravines formed by ephemeral and intermittent streams, and on toeslopes and north-facing backslopes. Generally, these systems are less than 50 meters (165 feet) wide, although the linear extent may be considerable. Soils are usually deep and loamy. Flooding is very short in duration when it occurs, as water is rapidly channeled downslope.

In Montana, this community is composed mostly of small trees, although larger diameter trees can occur at the foot of the ravine where there is greater available soil moisture. In some areas of the western Great Plains, in higher elevation draws and ravines, Rocky Mountain juniper can dominate the canopy. Aspen, paper birch or boxelder maple are commonly present in portions of the northwestern Great Plains. Throughout central and eastern Montana, green ash or chokecherry are the typical dominants, although Douglas hawthorne is occasionally seen as a dominant in south-central Montana, especially around the Pryor Mountains. Boxelder maple and American elm (Ulmus rubra or Ulmus americana) are often present. In many parts of Montana, particularly in disturbed occurrences, the understory is a dense shrub layer of western snowberry (Symphoricarpos occidentalis). In less disturbed sites, the understory is two-layered, with a shrub layer of chokecherry and other Prunus species, as well as hawthorne species, silverberry (Elaeagnus commutata), current (Ribes species), Woods' rose (Rosa woodsii), and silver buffaloberry (Shepherdia argentea). The lowest layer is dominated by sedges (Carex species) and grasses such as northern reedgrass (Calamagrostis stricta), western wheatgrass (Pascopyrum smithii), bluebunch wheatgrass (Pseudoroegneria spicata), and thickspike wheatgrass (Elymus lanceolatus). Common forbs include American licorice (Glycyrrhiza lepidota), yarrow (Achillea millefolium), meadow rue (Thalictrum dasycarpum), and bedstraw (Galium species). Exotics such as Russian olive (Elaeagnus angustifolia), yellow sweetclover (Meliotus officinalis) and Kentucky bluegrass (Poa pratensis) are often found throughout these systems, especially in agricultural areas.

Fire, wildlife and livestock use, and invasion by non-native species are major disturbances in this system. Both domestic animals and wildlife use this system readily, leading to trampling of vegetation and an increase in shrub and grass domination. Boxelder is highly susceptible to mechanical damage from livestock (Rosario, 1988), and in stands where green ash is dominant, heavy livestock grazing may prevent regeneration, leading to more open stands dominated by exotic perennial grasses (Lesica, 2009). A study in green ash dominated draws in the northern Great Plains found that exclusion of livestock increased tree height and decreased mortality for both green ash and elm (Uresk et al., 2009).

Fire is a secondary influence and may promote regeneration by encouraging sprouting and thinning of stands (Lesica, 2003). Fire return intervals in this system average approximately 30 years, and range from low-severity surface fires to stand-replacing burns (U.S. Department of Agriculture, 2012). Most species in this system are highly susceptible to fire, although green ash and Rocky Mountain juniper may survive low-intensity burns in some cases (Gucker, 2005; Scher, 2002). Despite experiencing high mortality due to fire, species in this system are fire-adapted and recover quickly via root sprouting, as is the case with aspen and green ash, or by prolific seed production and wind dispersal, as is the case with paper birch and boxelder. Most species in this system, however, are capable of utilizing both strategies to varying degrees (Gucker, 2005; Howard, 1996; Uchytil, 1991; Rosario, 1988).

In parts of eastern Montana, non-native species like Russian olive (Elaeagnus angustifolia) have invaded this system altering vegetation composition and changing biogeochemical cycling in streams (Mineau et al., 2011). Russian olive trees are fast-growing and form a dense canopy that prevents the more shade-intolerant native species typical of this system from establishing (Combs, 2010). Additionally, Russian olive exerts a strong competitive effect on native tree species in this system, inhibiting their establishment (Katz and Shafroth, 2003). Non-native grasses also alter species composition within this system, particularly where green ash is dominant, by forming dense sods and preventing seedling recruitment (Lesica, 2009).

Restoration of this system may in part require alternate grazing practices to allow for successful recovery. Dominant species such as chokecherry, Douglas hawthorne and elm have extensive root systems and are rated as good to excellent for soil erosion control. Aspen and paper birch are additionally recommended for revegetation and soil stabilization (Howard, 1996; Uchytil, 1991). In some cases, shrubs can be planted in clusters or bands in areas with high soil erosion potential. All other associated understory shrubs within this system - western snowberry, silverberry, gooseberry, Woods' rose, and silver buffaloberry - are rated as good to excellent restoration species, and possess strongly rhizomatous root systems that minimize soil erosion on steep slopes.

In order to promote regeneration in areas where green ash recruitment has been prevented by exotic grasses, Lesica (2009) recommends herbicide treatment followed by seeding. Alternatively, cutting of mature individuals encourages sprouting, which may be more successful than direct seeding. However, intensive browsing by ungulates may limit the success of this approach (Lesica, 2009). In wooded draws where Russian olive has become dominant, the most effective method of restoration employs a combination of chemical and mechanical treatments. Prescribed burning is not recommended as Russian olive readily resprouts post-fire (Katz and Shafroth, 2003). Combs (2010) recommends specific methods for reducing Russian olive where invasion into this system has occurred.