10 – Alpine Grasslands and Shrublands
Christopher B. Chappell & Jimmy Kagan
Geographic Distribution. This habitat occurs in high mountains
throughout the region, including the Cascades, Olympic Mountains, Okanogan
Highlands, Wallowa Mountains, Blue Mountains, Steens Mountain in southeastern
Oregon, and, rarely, the Siskiyous. It is most extensive in the Cascades from
Mount Rainier north and in the Wallowa Mountains. Similar habitats occur
throughout mountains of northwestern North America.
Physical Setting. The climate is the coldest of any habitat
in the region. Winters are characterized by moderate to deep snow
accumulations, very cold temperatures, and high winds. Summers are
relatively cool. Growing seasons are short because of persistent
snow pack or frost. Blowing snow and ice crystals on top of the
snow pack at and above treeline prevent vegetation such as trees
from growing above the depth of the snow pack. Snow pack protects
vegetation from the effects of this winter wind-related disturbance
and from excessive frost heaving. Community composition is much
influenced by relative duration of snow burial and exposure to wind
and frost heaving.75 Elevation ranges
from a minimum of 5,000 ft (1,524 m) in parts of the Olympics to
›10,000 ft (3,048 m). The topography varies from gently sloping
broad ridgetops, to glacial cirque basins, to steep slopes of all
aspects. Soils are generally poorly developed and shallow, though
in subalpine grasslands they may be somewhat deeper or better developed.
Geologic parent material varies with local geologic history.
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.
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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 Project126 and Oregon Vegetation
Landscape-Level Cover Types127 that would represent
this type are subalpine grassland and alpine fell-snowfields; represented by
nonforest 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
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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 vegetation80 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
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