Northern Rockies Subalpine Woodland and Parkland

This ecological system of the Northern Rockies, Cascade Range, and northeastern Olympic Mountains is typically a high-elevation mosaic of stunted tree clumps, open woodlands, and herb- or dwarf-shrub-dominated openings, occurring above closed forest ecosystems and below alpine communities. It includes open areas with clumps of Pinus albicaulis, as well as woodlands dominated by Pinus albicaulis or Larix lyallii. In the Cascade Range and northeastern Olympic Mountains, the tree clump pattern is one manifestation, but these are also woodlands with an open canopy, without a tree clump/opening patchiness to them; in fact, that is quite common with Pinus albicaulis. The climate is typically very cold in winter and dry in summer. In the Cascades and Olympic Mountains, the climate is more maritime in nature and wind is not as extreme. The upper and lower elevational limits, due to climatic variability and differing topography, vary considerably; in interior British Columbia, this system occurs between 1000 and 2100 m elevation, and in northwestern Montana, it occurs up to 2380 m. Landforms include ridgetops, mountain slopes, glacial trough walls and moraines, talus slopes, landslides and rockslides, and cirque headwalls and basins. Some sites have little snow accumulation because of high winds and sublimation. Larix lyallii stands generally occur at or near upper treeline on north-facing cirques or slopes where snowfields persist until June or July. 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. The stands or patches often originate when Picea engelmannii, Larix lyallii, or Pinus albicaulis colonize a sheltered site such as the lee side of a rock. Abies lasiocarpa can then colonize in the shelter of the Picea engelmannii and may form a dense canopy by branch-layering. Major disturbances are windthrow and snow avalanches. Fire is known to occur infrequently in this system, at least where woodlands are present; lightning damage to individual trees is common, but sparse canopies and rocky terrain limit the spread of fire.

These high-elevation coniferous woodlands are dominated by Pinus albicaulis, Abies lasiocarpa, and/or Larix lyallii, with occasional Picea engelmannii. In the Cascades and Olympics, Abies lasiocarpa sometimes dominates the tree layer without Pinus albicaulis, though in this dry parkland Tsuga mertensiana and Abies amabilis are largely absent. The undergrowth is usually somewhat depauperate, but some stands support a near sward of heath plants, such as Phyllodoce glanduliflora, Phyllodoce empetriformis, Empetrum nigrum, Cassiope mertensiana, and Kalmia polifolia, and can include a slightly taller layer of Ribes montigenum, Salix brachycarpa, Salix glauca, Salix planifolia, Vaccinium membranaceum, Vaccinium myrtillus, or Vaccinium scoparium that may be present to codominant. The herbaceous layer is sparse under dense shrub canopies or may be dense where the shrub canopy is open or absent. Vahlodea atropurpurea, Luzula glabrata var. hitchcockii, and Juncus parryi are the most commonly associated graminoids.

In the mountains of northwestern and west-central Wyoming, where this upper-treeline system reaches the edge of its geographic range, the vegetation usually has the form of an open woodland, and only rarely as scattered groves of trees. At the highest elevations, Pinus albicaulis usually has a wind-stunted shrub form. On lower, more favorable sites, upright but wind-shaped Pinus albicaulis forms woodlands, sometimes with Pinus contorta as a codominant or even the dominant species. With decreased altitude, where this system merges into the subalpine forests, Picea engelmannii and Abies lasiocarpa become common tree species as well.

These high-elevation coniferous woodlands are dominated by Pinus albicaulis, Abies lasiocarpa, and/or Larix lyallii, with occasional Picea engelmannii. In the Cascades and Olympics, Abies lasiocarpa sometimes dominates the tree layer without Pinus albicaulis, though in this dry parkland Tsuga mertensiana and Abies amabilis are largely absent. The undergrowth is usually somewhat depauperate, but some stands support a near sward of heath plants, such as Phyllodoce glanduliflora, Phyllodoce empetriformis, Empetrum nigrum, Cassiope mertensiana, and Kalmia polifolia, and can include a slightly taller layer of Ribes montigenum, Salix brachycarpa, Salix glauca, Salix planifolia, Vaccinium membranaceum, Vaccinium myrtillus, or Vaccinium scoparium that may be present to codominant. The herbaceous layer is sparse under dense shrub canopies or may be dense where the shrub canopy is open or absent. Vahlodea atropurpurea (= Deschampsia atropurpurea), Luzula glabrata var. hitchcockii, and Juncus parryi are the most commonly associated graminoids.

In the mountains of northwestern and west-central Wyoming, where this upper-treeline system reaches the edge of its geographic range, the vegetation usually has the form of an open woodland, and only rarely as scattered groves of trees. At the highest elevations, Pinus albicaulis usually has a wind-stunted shrub form. On lower, more favorable sites, upright but wind-shaped Pinus albicaulis forms woodlands, sometimes with Pinus contorta as a codominant or even the dominant species. With decrease in altitude, where this system merges into the subalpine forests, Picea engelmannii and Abies lasiocarpa become common tree species as well.

This ecological system of the Northern Rockies, Cascade Range, and northeastern Olympic Mountains is typically a high-elevation mosaic of stunted tree clumps, open woodlands, and herb- or dwarf-shrub-dominated openings, occurring above closed forest ecosystems and below alpine communities. The upper and lower elevational limits, due to climatic variability and differing topography, vary considerably from 1000-3200 m depending on latitude. In interior British Columbia, this system occurs between 1000 and 2100 m elevation, and in northwestern Montana, it occurs up to 2380 m. In west-central Wyoming, this system occurs on various landforms over an elevational range from 2230 to 3200 m (Steele et al. 1983).

Climate: The climate is typically very cold in winter and dry in summer. Mean annual precipitation ranges from 60-180 cm, occurring mostly in the winter. Yearly snow accumulations are often over 3 m in the northern Cascades and 2-3 m in the Rockies. Some sites have little snow accumulation because of high winds and sublimation. In the Cascades and Olympic Mountains, the climate is more maritime in nature and wind is not as extreme.

Physiography/Landform: Landforms include ridgetops, mountain slopes, glacial trough walls and moraines, talus slopes, landslides and rockslides, and cirque headwalls and basins. Sites may be nearly level to steep sloping, on all aspects. Some stands occur at treeline in mesic, protected pockets away from the extremely harsh environmental conditions. It is not tied to particular aspects (Steele et al. 1983).

Soil/substrate/hydrology: Soils are generally lithic, well-to excessively drained, and coarse-textured such as shallow, gravelly sands or loams, but may include silt and clay loams. Soils are derived from colluvium, glacial till and residuum from a variety of volcanic, igneous, sedimentary and metamorphic geologic formations.

Pinus albicaulis is a slow-growing, long-lived conifer that is common at higher elevations in the upper subalpine zone. It typically occurs in a mosaic of tree islands and meadows where it often colonizes sites and creates habitat for less hardy tree species. In lower subalpine forests, it is a seral species, establishing after a large disturbance such as stand-replacing fire or avalanche, 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 hot ground fires kill Pinus albicaulis, it tolerates low-intensity ground fires that will kill the shade-tolerant understory. Fire intervals range from 30-300 years.

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. The stands or patches often originate when Picea engelmannii, Larix lyallii, or Pinus albicaulis colonize a sheltered site such as the lee side of a rock. Abies lasiocarpa can then colonize in the shelter of the Picea engelmannii and may form a dense canopy by branch-layering. Major disturbances are windthrow and snow avalanches. Fire is known to occur infrequently in this system, at least where woodlands are present; lightning damage to individual trees is common, but sparse canopies and rocky terrain limit the spread of fire. Larix lyallii is a very slow-growing, long-lived tree, with individuals up to 1000 years in age. It is generally shade-intolerant; however, extreme environmental conditions limit potentially competing trees. In the Cascades and Olympic Mountains, the climate is more maritime in nature and wind is not as extreme, but summer drought is a more important process than in the related North Pacific Maritime Mesic Subalpine Parkland (CES204.837). In northwestern and west-central Wyoming, Pinus albicaulis is the initial colonizer, and trees of other species become established in the micro-sites that it creates (Callaway 1998, cited in Greater Yellowstone Coordinating Committee 2011). In the highest-elevation stands where Pinus albicaulis usually is the only tree present, vegetation dynamics are relatively simple: stands start out with rather dense overstories and sparse undergrowth and develop more open overstories and denser undergrowth over time. At lower elevations, Pinus contorta dominates some stands soon after fire, and the long-lived, more shade-tolerant Pinus albicaulis become dominant over time (Steele et al. 1983). As in the Pacific Northwest, fire has, in the past, been a minor process (compared to the subalpine forests at lower elevations): lightning starts many fires, but they rarely spread (Steele et al. 1983).

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, Burns and Honkala 1990a, Schmidt and McDonald 1990, Steel et al. 1983).

The mountain pine beetle (Dendroctonus ponderosae) has killed many mature trees in the past, during epidemics where populations of the beetles build up in lower elevation Pinus contorta stands, then move up into the Pinus albicaulis (Burns and Honkala 1990a, Schmidt and McDonald 1990, Steel et al. 1983).

From WNHP (2011): The primary land uses that alter the natural processes of this system are associated with exotic species, direct soil surface disturbance, timber management, livestock practices, and fragmentation. The introduced pathogen white pine blister rust (Cronartium ribicola) increases Pinus albicaulis mortality in these woodlands (Kendall and Keane 2001) and changes fire regime, mountain pine beetle (Dendroctonus ponderosae) effects and successional relationships. Exotic species threatening this ecological system through invasion and potential replacement of native species include Poa pratensis. Excessive grazing stresses the system through soil disturbance and perennial layers to the establishment of native disturbance-increasers (Lupinus spp., Juncus parryi, Achillea millefolium) in similar Northern Rocky Mountain systems (Johnson 2004). Persistent grazing will further diminish native perennial cover, expose bare ground, and increase erosion and exotics (Johnson and Swanson 2005). Grazing effects are usually concentrated in less steep slopes, although grazing does create contour trail networks that can lead to addition slope failures. Cattle and heavy use by elk can reduce fescue cover and lead to erosion during summer storms (Johnson and Swanson 2005). Introduction of exotic ungulates can have noticeable impacts (e.g., mountain goats in the Olympic Mountains and domestic sheep grazing in the bunchgrass habitats east of the Cascades). Historical domestic sheep grazing may have occurred in these systems but its cumulative effects are unknown (Landfire 2007a). Locally, trampling and associated recreational impacts can affect sites for decades or longer (Lillybridge et al. 1995). Sites are naturally low in timber productivity and in stocking rates such that removal of trees can have very long-lasting influence on ecological processes (Lillybridge et al. 1995).

Conversion of this type has commonly come from conversion to invasive non-native species such as Poa pratensis, which increase post disturbance including long-term excessive grazing by livestock, or direct soil disturbance from timber management, heavy recreational use, severe trampling by livestock, and roads. However, conversion is not a major factor for this system.

Common stressors and threats include fragmentation from roads, altered fire regime from fire suppression, and indirectly from livestock grazing and fragmentation the introduction of invasive non-native species (WNHP 2011). The introduced pathogen white pine blister rust causes considerable Pinus albicaulis mortality in these woodlands and parklands (Kendall and Keane 2001). Mountain pine beetle epidemics also cause significant Pinus albicaulis mortality, especially during dry years. Pinus albicaulis are large-seeded trees and are dependent on animals for longer distance dispersal. Threats to these dispersers such as Clark's nutcracker are threats to the regeneration of these pines and the ecosystem.

In this system in Wyoming and eastern Idaho (Steele et al. 1983), livestock grazing likely is a minor threat because there is little forage. Grazers can, though, easily degrade forb-dominated undergrowths, but the vegetation where Vaccinium scoparium dominates (as it does in a high proportion of stands) appears to be less susceptible to grazing and, in fact, has been shown to withstand heavy grazing by deer and elk. In Wyoming, 59% of the area predicted to support whitebark pine is within designated national forest wilderness areas or national parts (WNDD 2013). In the Greater Yellowstone area of Wyoming, Montana, and Idaho, 62% of the whitebark pine is within national parks or wilderness areas (Macfarlane et al. 2009, Appendix A; these authors apparently neglected to include 2 wilderness areas in Wyoming, so that percentage likely is higher). Hence a large percentage of this ecological system apparently is in areas managed to minimize threats. Heavy recreational use can damage undergrowth vegetation and cause soil erosion so severe that it prevents restoration (Steele et al. 1983), but such impacts likely are limited to few stands because of the management status of the lands and because, even outside of protected areas, Pinus albicaulis woodlands are largely inaccessible to most people.

White pine blister rust is a very serious threat, as only 26% of the Pinus albicaulis trees in the Greater Yellowstone area show resistance (Greater Yellowstone Coordinating Committee 2011). Monitored plots show infection rates ranging from 0-84% of trees and averaging 20% (several studies cited in Greater Yellowstone Coordinating Committee 2011). Because of blister rust, restoration projects in eastern Idaho and western Montana have failed to produce significant regeneration of Pinus albicaulis (Keane and Parsons 2010, cited in Rice et al. 2012). Mountain pine beetle, too, is a major threat to this ecological system in the Greater Yellowstone area. Aerial surveys in 2009 revealed that 50% of Pinus albicaulis stands had suffered severe to complete mortality of pines, and 95% of forest stands containing Pinus albicaulis had measurable pine beetle activity (Macfarlane et al. 2009, cited in Rice et al. 2011). Several species of Dendroctonus have also killed great numbers of Pinus contorta and Picea engelmannii, other constituents of the vegetation in this ecological system in the area.

Potential climate change effects in the Pacific Northwest region are based on downscaled climate models projecting increases in annual temperature of, on average, 3.2°F by the 2040s. Increases in extreme high precipitation (falling as rain) in the western Cascades and reductions in snowpack are key projections from high-resolution regional climate models (Littell et al. 2009). Warmer temperatures will result in more winter precipitation falling as rain rather than snow throughout much of the Pacific Northwest, particularly in mid-elevation basins where average winter temperatures are near freezing. This change will result in less winter snow accumulation, higher winter streamflows, earlier spring snowmelt, earlier peak spring streamflow, and lower summer streamflows in rivers that depend on snowmelt (Littell et al. 2009). These potential changes in climate could include Increased fire frequency due to warmer temperatures resulting in drier fuels; the area burned by fire regionally is projected to double by the 2040s and triple by the 2080s (Littell et al. 2009). Additionally, likely climatic warming may stress host trees, so mountain pine beetle outbreaks are projected to increase in frequency and cause increased tree mortality. Finally, the amount of habitat with climate ranges required for these subalpine tree species, especially Pinus albicaulis which is susceptible to mountain pine beetle, will likely decline substantially by mid 21st century.

The ways in which the climate in the region where this system reaches its eastern limit is likely to change, and the effects of those changes on the structure and function of this system, are all hard to predict, and only broad generalizations can be made (Rice et al. 2012). Average annual temperature likely will increase by 1.7°C by 2050, and by 1.1° to 5.5°C by the end of this century. Annual precipitation may increase by 10%, with wetter winters and drier summers, but less certainty can be assigned to possible precipitation changes than temperature changes. The greatest direct impact of these changes on this ecological system likely would be that Pinus albicaulis retreats from the lower-elevation parts of its range and exists only at the highest elevations or disappears. Climate changes will also affect the ecological system indirectly, through changes in the fire regime (in general, more frequent and larger fires are likely), bark beetle populations, blister rust populations, and other ecological agents. Changes in the extremes of temperature and precipitation likely will have a stronger effect than will changes in annual averages, and the patterns of these extremes are especially hard to predict. Climate changes almost certainly will disrupt the composition, structure, and function of the parkland ecological system, in ways that can only be very generally anticipated.

This system occurs in the northern Rocky Mountains, west into the Cascade Range and northeastern Olympic Mountains, and east into the mountain "islands" of central Montana.