No. 10. Alpine Grassland and Shrublands

Landscape Setting. This habitat always occurs above upper treeline in the mountains or a short distance below it (grasslands in the subalpine parkland zone). Typically, it occurs adjacent to, or in a mosaic with, Subalpine Parkland. Occasionally, it may grade quickly from this habitat down into Montane Mixed Conifer Forest without intervening Subalpine Parkland. In southeastern Oregon, this habitat occurs adjacent to and above Upland Aspen Forest and Shrub-steppe habitats. Small areas of Open Water, Herbaceous Wetlands, and Subalpine Parkland habitats sometimes occur within a matrix of this habitat. Cliffs, talus, and other barren areas are common features within or adjacent to this habitat. Land use is primarily recreation, but in some areas east of the Cascade Crest, it is grazing, especially by sheep.

Structure. This habitat is dominated by grassland, dwarf-shrubland (mostly evergreen microphyllous), or forbs. Cover of the various life forms is extremely variable, and total cover of vascular plants can range from sparse to complete. Patches of krummholz (coniferous tree species maintained in shrub form by extreme environmental conditions) are a common component of this habitat, especially just above upper treeline. In subalpine grasslands, which are considered part of this habitat, widely scattered coniferous trees sometimes occur. Five major structural types can be distinguished: (1) subalpine and alpine bunchgrass grasslands, (2) alpine sedge turf, (3) alpine heath or dwarf-shrubland, (4) fellfield and boulderfield, and (5) snowbed forb community. Fellfields have a large amount of bare ground or rocks with a diverse and variable open layer of forbs, graminoids, and less commonly dwarf-shrubs. Snowbed forb communities have relatively sparse cover of few species of mainly forbs. In the alpine zone, these types often occur in a complex fine-scale mosaic with each other.

Composition. Most subalpine or alpine bunchgrass grasslands are dominated by Idaho fescue (Festuca idahoensis), alpine fescue (F. brachyphylla), green fescue (F. viridula), Rocky Mountain fescue (F. saximontana), or timber oatgrass (Danthonia intermedia), and to a lesser degree, purple reedgrass (Calamagrostis purpurascens), downy oat-grass (Trisetum spicatum) or muttongrass (Poa fendleriana). Forbs are diverse and sometimes abundant in the grasslands. Alpine sedge turfs may be moist or dry and are dominated by showy sedge (Carex spectabilis), black alpine sedge (C. nigricans), Brewer’s sedge (C. breweri), capitate sedge (C. capitata), nard sedge (C. nardina), dunhead sedge (C. phaeocephala), or western single-spike sedge (C. pseudoscirpoidea).

One or more of the following species dominates alpine heaths: pink mountain-heather (Phyllodoce empetriformis), green mountain-heather (P. glanduliflora), white mountain-heather (Cassiope mertensiana), or black crowberry (Empetrum nigrum). Other less extensive dwarf-shrublands may be dominated by the evergreen coniferous common juniper (Juniperus communis), the evergreen broadleaf kinnikinnick (Arctostaphylos uva-ursi), the deciduous shrubby cinquefoil (Pentaphylloides floribunda) or willows (Salix cascadensis and S. reticulata ssp. nivalis). Tree species occurring as shrubby krummholz in the alpine are subalpine fir (Abies lasiocarpa), whitebark pine (Pinus albicaulis), mountain hemlock (Tsuga mertensiana), Engelmann spruce (Picea engelmannii), and subalpine larch (Larix lyallii).

Fellfields and similar communities are typified by variable species assemblages and co-dominance of multiple species, including any of the previously mentioned species, especially the sedges, as well as golden fleabane (Erigeron aureus), Lobb’s lupine (Lupinus sellulus var. lobbii), spreading phlox (Phlox diffusa), eight-petal mountain-avens (Dryas octopetala), louseworts (Pedicularis contorta, P. ornithorhyncha) and many others. Snowbed forb communities are dominated by Tolmie’s saxifrage (Saxifraga tolmiei), Shasta buckwheat (Eriogonum pyrolifolium), or Piper’s woodrush (Luzula piperi).

Other Classifications and Key References. This habitat is equivalent to the alpine communities and the subalpine Festuca communities of Franklin and Dyrness ⁸⁸. It is also referred to as Alpine meadows and barren No. 52 ¹³⁶. The Oregon Gap II Project ¹²⁶ and Oregon Vegetation Landscape-Level Cover Types ¹²⁷ that would represent this type are subalpine grassland and alpine fell-snowfields; represented by non-forest in the alpine/parkland zone of Washington Gap ³⁷. Other references describe this habitat ^{61, 65, 75, 80, 94, 105, 112, 123, 139, 195, 207}.

Natural Disturbance Regime. Most natural disturbances seem to be small scale in their effects or very infrequent. Herbivory and associated trampling disturbance by elk, mountain goats, and occasionally bighorn sheep seems to be an important disturbance in some areas, creating patches of open ground, though the current distribution and abundance of these ungulates is in part a result of introductions. Small mammals can also have significant effects on vegetation: e.g., the heather vole occasionally overgrazes heather communities ⁸⁰. Frost heaving is a climatically related small-scale disturbance that is extremely important in structuring the vegetation ⁸⁰. Extreme variation from the norm in snow pack depth and duration can act as a disturbance, exposing plants to winter dessication ⁸⁰, shortening the growing season, or facilitating summer drought. Subalpine grasslands probably burn on occasion and can be formed or expanded in area by fires in subalpine parkland ¹³⁹.

Succession and Stand Dynamics. Little is known about vegetation changes in these communities, in part because changes are relatively slow. Tree invasion rates into subalpine grasslands are relatively slow compared to other subalpine communities ¹³⁹. Seedling establishment for many plant species in the alpine zone is poor. Heath communities take about 200 years to mature after initial establishment and may occupy the same site for thousands of years ¹³⁹.

Effects of Management and Anthropogenic Impacts. The major human impacts on this habitat are trampling and associated recreational impacts, e.g., tent sites. Resistance and resilience of vegetation to impacts varies by life form ⁴⁸. Sedge turfs are perhaps most resilient to trampling and heaths are least resilient. Trampling to the point of significantly opening an alpine heath canopy will initiate a degradation and erosion phase that results in continuous bare ground, largely unsuitable for vascular plant growth ⁸⁰. Bare ground in the alpine zone left alone after recreational disturbance will typically not revegetate in a time frame that humans can appreciate. Introduction of exotic ungulates can have noticeable impacts (e.g., mountain goats in the Olympic Mountains). Domestic sheep grazing has also had dramatic impacts ¹⁹⁶, especially in the bunchgrass habitats east of the Cascades.

Status and Trends. This habitat is naturally very limited in extent in the region. There has been little to no change in abundance over the last 150 years. Most of this habitat is still in good condition and dominated by native species. Some areas east of the Cascade Crest have been degraded by livestock use. Recreational impacts are noticeable in some national parks and wilderness areas. Current trends seem to be largely stable, though there may be some slow loss of subalpine grassland to recent tree invasion. Threats include increasing recreational pressures, continued grazing at some sites, and, possibly, global climate change resulting in expansion of trees into this habitat. Only 1 out of 40 plant associations listed in the National Vegetation Classification is considered imperiled  ¹⁰.