Montana Field Guide

This group is characterized by forests and woodlands dominated by Whitebark Pine (Pinus albicaulis) or Subalpine Larch (Larix lyallii), individually or in combination. Other conifers, primarily Subalpine Fir (Abies lasiocarpa) and Engelmann Spruce (Picea engelmannii) may be present, especially in Whitebark Pine stands. It occurs frequently on both sides of the Continental Divide in the subalpine zone of the higher mountain ranges and typically forms the highest elevation forested communities in many mountain ranges. Stands typically occur between elevations of 6,000 to 9,500ft. on mid to upper slopes, shoulder slopes, ridges, and exposed high-elevation benches on all aspects. Trees are often stunted and flagged as a result of harsh cold and wind at timberline. Stands in more protected sites or below timberline may reach 50ft or more in height. The understory is variable depending on substrates ranging from sparse on rockier sites to dense on more mesic sites and typically characterized by low-growing, ericaceous shrubs, graminoids and sparse forbs. Fire is infrequent in this group, though it is important in maintaining some stands and removing competition from more shade tolerant conifers. However, sparse canopies and rocky terrain limits the spread of fire at many sites.

This Group is similar to the Rocky Mountain Subalpine Woodland and Parkland Ecological System.

Conifer Forest and Woodland; Rocky Mountains; Subalpine Zone, Timberline; Mixed Severity Fires.

Typical Dominants: Whitebark Pine (Pinus albicaulis), Subalpine Larch (Larix lyallii)

In Montana, this Group occurs frequently on both sides of the Continental Divide in the subalpine zone of the higher mountain ranges. It often forms the highest elevation forested communities in many mountain ranges. It extends east to the Little Belt Mountains, the Crazy Mountains and the Beartooth Plateau where it forms extensive stands. Whitebark Pine occurs in the Sweetgrass Hills and the Big Snowy Mtns but does not appear to be abundant or extensive enough to form communities. Communities containing Subalpine Larch occur mostly west of the Continental Divide but can be found in limited stands east of the Divide in Glacier National Park and in the Bob Marshall Wilderness Complex. Further south it can be found as far east as the Flint Creek Range, the Pintlers and the Beaverhead (Big Hole) Mtns.

In MT, G223 occurs within these Level III Ecoregions: 15 (Northern Rockies), 16 (Idaho Batholith), 17 (Middle Rockies) and 41 (Canadian Rockies).

In Montana, G223 occurs within these Major Land Resource Areas: 43A-Northern Rocky Mountains, 43B - Central Rocky Mountains.

Large Patch

This subalpine forest and woodland group typically occurs between elevations of 6,000 to 9,500ft. Stands occur on mid to upper slopes, shoulder slopes, ridges, and exposed high-elevation benches on all aspects. These sites are often subject to desiccating winds, heavy snowpack, and extreme diurnal temperate fluctuations. Substrates include a variety of igneous, metamorphic, and sedimentary geologic formations. Soils are well- to excessively drained and can include coarse sand, silt and clay loams. The climate is typically very cold and snowy in winter and relatively dry in summer. Yearly snow accumulations are typically greater than 6ft . Some sites have little snow accumulation because of high winds and sublimation. In this harsh, often windswept environment, trees are often stunted and flagged from damage associated with wind and blowing snow and ice crystals, especially at the upper elevations of the type. Where Subalpine Larch is dominant, soils are poorly developed and almost exclusively of fractured granitic or quartzite rocks which have not been previously colonized by other vascular plants. The majority of sites where Subalpine Larch occurs are in areas which experienced heavy alpine glaciation less than 12,000 years ago.

This group is characterized by forests and woodlands dominated by Whitebark Pine (Pinus albicaulis) or Subalpine Larch (Larix lyallii), individually or in combination. Other conifers, primarily Subalpine Fir (Abies lasiocarpa) and Engelmann Spruce (Picea engelmannii) may be present, especially in Whitebark Pine stands. Trees are often stunted and flagged as a result of harsh cold and wind at timberline. Stands in more protected sites or below timberline may reach 50ft or more in height. The understory is variable depending on substrates ranging from sparse on rockier sites to dense on more mesic sites and typically characterized by heaths and graminoids and sparse forbs. Shrubs and subshrubs common in these sites include Kinnikinnick (Arctostaphylos uva-ursi), Pink Mountain-heath (Phyllodoce empetriformis), Grouse Whortleberry (Vaccinium scoparium) and False Huckleberry (Menziesia ferruginea). The herbaceous layer is sparse under dense shrub canopies or may be dense where the shrub canopy is open or absent. Common species include Beargrass (Xerophyllum tenax), Ross’s Sedge (Carex rossii), Pinegrass (Calamagrostis rubescens), woodrush (Luzula hitchcockii), Mountain Arnica (Arnica latifolia) and Alpine Hawkweed (Hieracium gracile). Non-native species are generally absent or incidental in these high-elevation forests.

In Montana, this group is composed of 17 Associations grouped into 2 Alliances within the National Vegetation Classification, which likely covers the diversity of types within this group in the state.

Whitebark Pine is a slow-growing, long-lived conifer that is common at higher elevations in the upper subalpine zone. It occurs as extensive forests or as a mosaic of tree islands. In lower subalpine forests, it is a seral species, establishing after a large disturbance such as stand-replacing fire, or it is restricted to dry, rocky ridges where it competes well with shade-tolerant tree species. Without disturbance, it will be overtopped in 100-120 years by faster growing, shade-tolerant species such as Abies lasiocarpa, Picea engelmannii, Pseudotsuga menziesii, and Tsuga mertensiana. Although crown fires and high-intensity surface fires kill Whitebark Pine, it tolerates low-intensity surface fires that will kill the shade-tolerant understory. Fire intervals range from 30-300 years.

Birds and small mammals often eat and cache the large, wingless pine seeds and are responsible for the dispersal of this species. Most important is the Clark's nutcracker, which can transport the seeds long distances and cache them on exposed windswept and burned-over sites. This results in the regeneration of pines in clumps from forgotten caches (Eyre 1980, Steel et al. 1983, Burns and Honkala 1990a, Schmidt and McDonald 1990).

Pests include the mountain pine beetle (Dendroctonus ponderosae), which has killed many mature trees in the past, during epidemics where populations of the beetle build up in lower elevation Pinus contorta stands, then move up into the Pinus albicaulis (Steel et al. 1983; Burns and Honkala 1990a; Schmidt and McDonald 1990). The exotic pathogen white pine blister rust (Cronartium ribicola) is attacking and killing Whitebark Pine trees in many parts of the interior northwestern U.S. It is especially destructive in more mesic habitats that favor infection of its alternate host Ribes spp (Currants and Gooseberries). Whitebark Pine is very susceptible to this disease and high rates of mortality have occurred across large portions of its range. (Steel et al. 1983; Burns and Honkala 1990a; Schmidt and McDonald 1990; Tomback et al. 2001).

Subalpine Larch is a very slow-growing, long-lived tree, with individuals attaining up to 1000 years in age (Richards 1981). It is generally intolerant of shade from other trees, but extreme environmental conditions limit competition. Reproduction is typically by seed and is most favorable on moist mineral soil. Seedling growth is initially very slow and accelerates after an extensive root system is established. Major disturbances to stands of this group are windthrow and snow avalanches. Lightning damage to individual trees is common, but sparse canopies and rocky terrain serve to limit the spread of fire.

In the absence of natural fire, periodic low-severity prescribed burns can be implemented during late fall months to maintain, enhance, and restore this system. Fire facilitates nutrient cycling and encourages whitebark pine dominance in stands where succession by subalpine fir and Engelmann spruce is occurring (Arno and Hoff 1989). Fire additionally creates open sites favorable to seed caching by Clark’s nutcrackers and exposes mineral soil seedbeds favored by whitebark pine and alpine larch. A long-term study in western Montana and eastern Idaho found that prescribed fire is likely most effective at restoring whitebark pine if burn sites are in close proximity to healthy whitebark stands, or if burning is followed by planting of rust-resistant nursery stock (Keane and Parsons 2010). When selecting seed sources for supplemental planting, seed transfer guidelines should be followed to avoid maladaptation to site specific conditions (Bower and Aitken 2008).

Restoration strategies within Whitebark Pine stands will in part depend on degree of blister rust infection. Small-scale prescribed burning during late fall after several hard frosts is recommended to prevent succession by subalpine fir and facilitate whitebark pine regeneration by providing open sites on exposed mineral soils suitable for nutcracker seed caching and seedling establishment (Fryer 2002). Blister rust damage reduces cone production and nutcracker seed caching (McKinney and Tomback 2007). When blister rust infection within a region is severe, post-burn supplemental planting with genetically rust-resistant nursery stock may be necessary (Keane and Parsons 2010). Similarly, large scale mountain pine beetle outbreaks may necessitate supplemental planting if regeneration is limited or blister-rust infection of surviving individuals is severe. When outplanting rust-resistant nursery stock is necessary, success can be improved by reducing seedling competition with overstory trees or understory grasses and sedges, and planting seedlings in microsites with favorable growth conditions, including on the leeward side of rocks and stumps (McCaughey et al. 2009).

M.E. Hall and M.S. Reid 2013

S. Mincemoyer, T. Luna, M. Hart, L. Vance

12/4/2024