Montana Field Guide

Limber Pine Woodlands in this group occur intermittently from the lower montane zone to upper timberline. They occur east of the Continental Divide primarily on limestone-derived soils and can be found from the foothills of the Rocky Mountain Front, south to the mountains of extreme southwest Montana (Italian Peaks) and east to the island ranges including the Snowy Mtns and the Pryor Mtns. Elevations range from about 4,500ft in central Montana to over 8,500ft in the southwest. Sites are xeric and occur on exposed, windswept slopes and ridges to gentle slopes such as along the Rocky Mountain Front. They occur on all aspects but are most common on dry south- and west-facing slopes, especially at higher elevations. Soils are typically shallow, skeletal and coarse-textured, such as gravelly, sandy loams or loams, but may include alkaline clays. Exposed rock, gravel and soil are common. The vegetation is characterized by an open canopy of relatively short-statured Limber Pine (Pinus flexilis) up to about 50ft tall. Other tree species that may be present or codominant on some sites include Whitebark Pine (Pinus albicaulis), Engelmann Spruce (Picea engelmannii), and Douglas-fir (Pseudotsuga menziesii). The understory vegetation is typically sparse as the sites are dry with shallow, rocky soils.

Sites that are co-dominated by Rocky Mountain Juniper or Utah Juniper are part of G209 as are arid communities of Limber Pine/Bluebunch Wheatgrass.

This Group incorporates the higher elevation plant associations included within the Rocky Mountain Foothill Limber Pine - Juniper Woodland Ecological System.

Xeric Conifer Forest and Woodland; Montane and Subalpine Zones; Upper Timberline; Rocky Mtn Region

Typical Dominants: Limber Pine (Pinus flexilis)

In Montana, this group occurs east of the Continental Divide at montane and subalpine elevations primarily on limestone-derived soils. It can be found from the foothills of the Rocky Mountain Front, south to the mountains of extreme southwest Montana (Italian Peaks) and east to the island ranges including the Snowy Mtns and the Pryor Mtns.

In Montana, G101 occurs in Level III Ecoregions: 17 (Middle Rockies) and 41 (Canadian Rockies).

In Montana, G101 occurs within these Major Land Resource Areas: 43B - Central Rocky Mountains, and higher elevations of 46 - Northern and Central Rocky Mountain Foothills.

Large Patch

Communities in this group occur intermittently from the lower montane zone to upper timberline. They occur east of the Continental Divide primarily on limestone-derived soils and can be found from the foothills of the Rocky Mountain Front, south to the mountains of extreme southwest Montana (Italian Peaks) and east to the island ranges including the Snowy Mtns and the Pryor Mtns. Elevations range from about 4,500ft in central Montana to over 8,500ft in the southwest. Sites are xeric and occur on exposed, windswept slopes and ridges to gentle slopes such as along the Rocky Mountain Front. They occur on all aspects but are most common on dry south- and west-facing slopes. Soils are typically calcareous, shallow, skeletal and coarse-textured, ranging from sandy loams to silts. Exposed rock, gravel and soil are common with only a minor or patchy layer of duff and litter. This group occurs in a semiarid, cold temperate climate. Annual precipitation amounts and patterns are variable as stands occur at wide range of elevations.

These communities are dominated by an open canopy of relatively short-statured Limber Pine (Pinus flexilis) up to a maximum height of about 50ft, though are mostly much shorter. Rocky Mountain Juniper and Utah Juniper are absent or of minor importance in these mostly higher elevation Limber Pine communities. Other tree species that may be present or codominant on some sites include Whitebark Pine (Pinus albicaulis), Engelmann Spruce (Picea engelmannii), and Douglas-fir (Pseudotsuga menziesii). The understory vegetation is typically sparse as the sites are dry with shallow, rocky soils.

A sparse, short, shrub layer may be present that typically includes Common Juniper (Juniperus communis), Kinnikinnick (Arctostaphylos uva-ursi), Creeping Oregon-grape (Berberis repens) and Mountain Snowberry (Symphoricarpos oreophilus), and stands along the Rocky Mountain Front may also have Creeping Juniper (Juniperus horizontalis). The herbaceous layer is composed primarily of graminoids such as Idaho fescue (Festuca idahoensis), Rough Fescue (Festuca campestris), and Spike Fescue (Leucopoa kingii). Perennial forbs have sparse cover. In the Pryor Mountains, Achillea millefolium, Agoseris glauca, Allium cernuum, Arnica cordifolia, Eurybia conspicua, Galium boreale, and Senecio streptanthifolius are common components (DeVelice and Lesica 1993, Pfister etal 1977). Annual forbs and grasses may be seasonally present.

In Montana, this group is represented by 1 Alliance with 7 Associations, which likely covers the range of vegetation types found within this group in the state.

Although some of the conifers that are present or codominant in Limber Pine stands are late-successional species, they are unlikely to displace it. as most of these stands occur on harsh sites where Limber Pine is more competitive than the other conifer species. These stands are generally considered to be topographic or edaphic "climax" stands (Cooper 1975; Eyre 1980). Because Limber Pine occurs over a broad range of elevations, it can also be important as a post-fire seral species on drier sites in the Rocky Mountains (Cooper 1975; Peet 1988). Birds and small mammals often eat and cache the large, wingless pine seeds. Most important is the Clark's nutcracker, which can transport the seeds long distances and cache them on exposed windswept sites (Lanner and Vander Wall 1980). This results in the regeneration of pines in clumps from forgotten caches (Eyre 1980; Steele et al. 1983). Fires are generally of low frequency and low severity in these communities due to low fuel loads and the patchiness of the fuels. 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.

In the absence of natural fire, periodic low to moderate intensity prescribed burns can be implemented during late summer and 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 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). 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.

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).

K. Schulz

S. Mincemoyer

12/4/2024