Montana Field Guide

This group occurs in the foothills and lower montane zones in the Rocky Mountain and Intermountain Regions in the southern half of Montana, and on escarpments extending out onto the western Great Plains. It occurs primarily east of the Continental Divide though some communities dominated by Rocky Mtn Juniper also occur west of the Divide. Vegetation is characterized by an open-tree canopy or patchy woodland that is dominated by Limber Pine (Pinus flexilis) and/or Rocky Mountain Juniper (Juniperus scopulorum). In the Pryor Mountains, Utah Juniper (Juniperus osteosperma) reaches its northern extent and may be present or co-dominate on some sites, though stands dominated solely by Utah Juniper are part of G105. Douglas-fir (Pseudotsuga menziesii) and Ponderosa Pine (Pinus ponderosa) may be present at some sites. Elevations of sites range from 4,000ft to as high as approximately 6,500ft in southwest Montana. At lower elevations, it can occur on all aspects and on relatively level terrain. Stands of Limber Pine at higher elevations, lacking Rocky Mtn Juniper and with a mostly different component of undergrowth species are part of G101. In Montana, limber pine stands are found mainly on calcareous substrates. Soils generally have a high rock component (generally over 50% cover) and are coarse- to fine-textured, often gravelly.

This Group incorporates the lower and drier plant associations included within the Rocky Mountain Foothill Limber Pine - Juniper Woodland Ecological System

Xeric Conifer Forest and Woodlands; Foothills and Lower Montane Zones, Great Plains Rocky Mtn and Intermountain Region; Low to Moderate Canopy Cover; Calcareous Soils; Gravel, Rock and Bare Soil Common; Soils with an A-Horizon <10cm.

Typical Dominants: Limber Pine (Pinus flexilis), Rocky Mtn Juniper (Juniperus scopulorum), Utah Juniper (Juniperus osteosperma)

This Group occurs in the foothills and lower montane zones east of the Continental Divide and onto the plains. It is common along the lower elevations of several of the Island Ranges and on escarpments extending out into the western Great Plains. It is common in and near the Pryor Mountains in south-central Montana. This group also occurs in scattered locations west of the Divide and is represented by communities dominated by Rocky Mtn Juniper.

In Montana, G209 occurs in Level III Ecoregions: 17 (Middle Rockies), 18 (Wyoming Basin), 41 (Canadian Rockies), 42 (Northwestern Glaciated Plains), and 43 (Northwestern Great Plains).

In Montana, G209 occurs within these Major Land Resource Areas: 32 - Northern Intermountain Desertic Basins, 43B-Central Rocky Mountains, 46 - Northern and Central Rocky Mountain Foothills; 52 – Brown Glaciated Plains, 58A - Northern Rolling High Plains, Northern Part.

Large Patch

Communities in G209 are found on sites with elevations from 4,000ft to as high as approximately 6,500ft in southwest Montana. At lower elevations, it can occur on all aspects and on relatively level terrain. In Montana, limber pine stands are found mainly on calcareous substrates. Rocky Mountain juniper stands are often found in complex transitional zones or growing on exposed or severe sites within other forest systems. These juniper stands can exhibit a savanna-like character in southwestern Montana. Soils generally have a high rock component (generally over 50% cover) and are coarse- to fine-textured, often gravelly. They are generally poorly developed, shallow, have low moisture holding capacity and are easily erodible, so in some occurrences, little topsoil is present. Although this group can be seen on gently rolling terrain, limestone cliffs, and exposed bluffs, it is most often found on rocky ridges and steep rocky slopes, and can survive in extremely windswept areas at the lower treeline. Climate is characterized by a relatively small amount of precipitation, with the wettest months during the growing season, very low humidity, and wide annual and diurnal temperature ranges.

Vegetation is characterized by an open-tree canopy or patchy woodland that is dominated by Limber Pine (Pinus flexilis) and/or Rocky Mountain Juniper (Juniperus scopulorum). In the Pryor Mountains, Utah Juniper (Juniperus osteosperma) reaches its northern extent and may be present or co-dominate on some sites. Douglas-fir (Pseudotsuga menziesii) and Ponderosa Pine (Pinus ponderosa) may be present at some sites. A sparse to moderately dense short-shrub layer is usually present. In southern Montana, Big Sagebrush (Artemisia tridentata), Black sagebrush (Artemisia nova), Curl-leaf Mountain Mahogany (Cercocarpus ledifolius), Broom Snakeweed (Gutierrezia sarothrae) and Plains Pricklypear (Opuntia polyacantha) are commonly present. The herbaceous layer is generally sparse and typically dominated by perennial graminoids such as Sandberg’s bluegrass (Poa secunda), Bluebunch Wheatgrass (Elymus spicatus), Prairie Junegrass (Koeleria macrantha), Purple Threeawn (Arista purpurea), Blue Grama (Bouteloua gracilis), Spike Fescue (Leucopoa kingii), Indian ricegrass (Oryzopsis hymenoides), and Threadleaf Sedge (Carex filifolia). Forb diversity can be very high. Some common forbs include Arenaria hookeri, Astragalus spp, Cryptantha spp, Erigeron spp, Eriogonum ovalifolium, Gaura coccinea, Locoweeds (Oxytropis spp). Phlox spp, Petrophytum caespitosum, Penstemon spp, Senecio canus, Stenotus spp, and Tetraneuris acaulis. Bryophyte and lichen cover are usually sparse (DeVelice and Lesica 1993, Pfister et al, 1977).

In Montana, 9 Associations grouped into 3 Alliances are currently recognized. These are relatively well-described and likely represent the overall diversity of the group within Montana.

Major disturbances in this system include fire, soil erosion from over-used range, and biotic vectors. Fire is infrequent and spotty as the semi-arid environment and rocky substrates inhibit growth of a continuous canopy and the fine fuels that are needed for continuous fire spread. However, some of these woodlands often originate with and are likely maintained by fire. Regeneration on burns within Limber Pine stands is largely from germination of seedlings from Clark's nutcracker seed caches. Clark's nutcrackers are the primary harvester and disperser of its seeds. Fire can easily kill young Limber Pine and Rocky Mountain Juniper because of their thin bark (Fischer and Clayton, 1983), however, fuel loads in this system are generally light due to open rocky terrain, and fires do not generate severe damage or considerably alter vegetation composition. In comparison with upper treeline Limber Pine communities, foothill populations are thought to experience greater disturbance frequency (Schuster et al., 1995), and fire return intervals vary between 50 and 400 years (U.S. Department of Agriculture, 2012). Over time Limber Pine woodlands have shifted both up- and down-slope in response to changing climate and drought, and are considered to be particularly sensitive to future change (Means 2010).

Limber Pine occurs on dry, rocky sites that are typified by extreme winter weather and droughty summer conditions that offer marginal conditions for tree growth. Consequently, mortality from abiotic and biotic stressors is high in some areas. Limber pine is highly susceptible to white pine blister rust (Cronartium ribicola), the pine needle pathogen (Dothistroma septospora), and mountain pine beetles (Dendroctonus ponderosae). It can also be heavily infected or killed by limber pine dwarf-mistletoe (Arceuthobium cyanocarpum), particularly in south-central and southwestern Montana (Jackson et al., 2010), and is susceptible to infestation by cone beetles (Conophthorus contortae), the ponderosa pine cone worm (Dioryctria auranticella), and the western conifer seed bug (Leptoglossus occidentalis). Resistance to blister rust and mountain pine beetle is lower for Limber Pine than for other North American pines affected by these biotic agents (Hoff and McDonald 1993; Means 2010), and drought can exacerbate vulnerability to pine beetle attack (Jackson et al., 2010). The most significant damage due to biotic factors appears to occur at locations on the Lewis and Clark National Forest along the northern Rocky Mountain Front, the Gravelly range and sections of the Yellowstone ecosystem in southwestern Montana. Large numbers of trees have very thin crowns and poor terminal growth, and severe mortality is occurring in some areas.

Under natural conditions, Rocky Mountain Juniper seedlings become established on moist sites in partial shade (Burns and Honkala 1990). Stands found in southwestern Montana may exhibit a savanna-like character due to the inability of Rocky Mountain Juniper to establish on drier micro-sites. Rocky Mountain Juniper is generally shallow rooted, and forest health can be negatively affected by heavy grazing, especially on exposed sites with erodible soils. Although Rocky Mountain juniper is relatively resistant to disease and tolerant of insects, several insect pests do attack this species including cedar flathead borers (Chrysobothris spp.) and bark beetles (Phloeosinus spp.) (Scher, 2002). Additionally, mistletoes (Phoradendron spp.), a blight caused by Cercospora sequoia, and cedar apple rust (Gymnosporangium juniper virgiananae) can be especially problematic (Burns and Honkala 1990).

In the absence of natural fire, periodic low to moderate intensity prescribed burns can be implemented during late fall months to maintain and enhance Limber Pine regeneration, although results may be variable due to insufficient ground fuels and rocky terrain typical of these communities. Fire may kill younger Limber Pine and Rocky Mountain Juniper because of their thin bark. Thinning may also be used in particularly dense stands to reduce spread of mountain pine beetles (Bureau of Land Management, 2011). In light of blister rust prevalence, stands can be managed to maintain Limber Pine forest composition, and to diversify age structure to include regeneration, thereby encouraging natural selection of rust resistant individuals (Jackson et al., 2010). On sites with slopes and forage that support domestic livestock, use can be monitored to maintain soil integrity. Prolonged drought and white pine blister rust (Cronartium rubicola) have decimated limber pine along the Rocky Mountain Front (and elsewhere), resulting in a skeleton woodland with scattered Douglas-firs as the only living trees.

Reintroduction of prescribed fire fosters Limber Pine regeneration because it provides open sites and exposed mineral soils that are suitable for Clark's nutcracker to cache seeds, and for seedlings to establish. Augmenting natural Limber Pine regeneration with seed sources that exhibit some resistance to blister rust or, in some cases, with nursery stock, will be necessary in areas where seed sources are absent or greatly reduced. Blister rust-resistant or tolerant trees can be identified in previously infected stands, or by screening for an identified resistance gene (Schoettle and Sniezko 2007; Schoettle et al. 2014). Direct seeding may be the most practical restoration method on most sites, however seed-transfer guidelines should be considered when the seed source is a considerable distance from the seeding site (Schoettle and Sniezko 2007). Germination will take place during the first growing season after fall caching or direct seeding.

Because this system is characterized by shallow soils, outplanting of nursery stock may be limited to microsites with deeper soil pockets. Out-planted seedling survival has been shown to be higher when seedlings are planted on microsites with some cover, when seedlings are planted in clumps rather than singly, and when competition from surrounding vegetation is minimized (Asebrook et al. 2011). Seedling health was marginally improved in burned areas compared to unburned areas within an experimental area in Waterton Lakes National Park, Alberta (Asebrook et al. 2006).

D.H. Knight (1994) and M.S. Reid and K.A. Schulz

S. Mincemoyer

12/3/2024