09 – Subalpine Parkland
Rex C. Crawford & Christopher B. Chappell
Geographic Distribution. The Subalpine Parkland habitat occurs
throughout the high mountain ranges of Washington and Oregon (e.g., Cascade
crest, Olympic Mountains, Wallowa and Blue mountains, and Okanogan Highlands),
extends into mountains of Canada and Alaska, and to the Sierra Nevadas and Rocky
Mountains.
Physical Setting. Climate is characterized by cool
summers and cold winters with deep snowpack, although much variation exists
among specific vegetation types. Mountain hemlock sites receive an average
precipitation of >50 inches (127 cm) in 6 months and several feet of snow
often accumulates. Whitebark pine sites receive 24-70 inches (61-178 cm) per
year and some sites only rarely accumulate a significant snowpack. Summer soil
drought is possible in eastside parklands but rare in westside areas. Elevation
varies from 4,500 to 6,000 ft (1,371 to 1,829 m) in the western Cascades and
Olympic Mountains and from 5,000 to 8,000 ft (1,524 to 2,438 m) in the eastern
Cascades and Wallowa mountains. Landscape Setting. The Subalpine
Parkland habitat lies above the Mixed Montane Conifer Forest or Lodgepole Pine
Forest habitat and below the Alpine Grassland and Shrubland habitat. Associated
wetlands in subalpine parklands extend up a short distance into the alpine zone.
Primary land use is recreation, watershed protection, and grazing.
Structure. Subalpine Parkland habitat has a tree layer
typically between 10 and 30% canopy cover. Openings among trees
are highly variable. The habitat appears either as parkland, that
is, a mosaic of treeless openings and small patches of trees often
with closed canopies, or as woodlands or savanna-like stands of
scattered trees. The ground layer can be composed of (1) low to
matted dwarf- shrubs (<1 ft [0.3 m] tall) that are evergreen
or deciduous and often small-leaved; (2) sod grasses, bunchgrasses,
or sedges; (3) forbs; or (4) moss- or lichen-covered soils. Herb
or shrub-dominated wetlands appear within the parkland areas and
are considered part of this habitat; wetlands can occur as deciduous
shrub thickets up to 6.6 ft (2 m) tall, as scattered tall shrubs,
as dwarf shrub thickets, or as short herbaceous plants <1.6 ft
(0.5 m) tall. In general, western Cascades and Olympic areas are
mostly parklands composed of a mosaic of patches of trees interspersed
with heather shrublands or wetlands, whereas, eastern Cascades and
Rocky mountain areas are parklands and woodlands typically dominated
by grasses or sedges, with fewer heathers.
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Composition.
Species composition in this habitat varies with geography or local site
conditions. The tree layer can be composed of one or several tree species.
Subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea
engelmannii) and lodgepole pine (Pinus contorta) are found throughout
the Pacific Northwest, whereas limber pine (P. flexilis) is restricted to
southeastern Oregon. Alaska yellowcedar (Chamaecyparis nootkatensis),
Pacific silver fir (A. amabilis), and mountain hemlock (Tsuga
mertensiana) are most common in the Olympics and western Cascades. Whitebark
pine (P. albicaulis) is found primarily in the eastern Cascades
mountains, Okanogan Highlands, and Blue Mountains. Subalpine larch (Laryx
lyallii) occurs only in the northern Cascade Mountains, primarily east of
the crest.
West Cascades and Olympic areas generally are parklands. Tree
islands often have big huckleberry (Vaccinium membranaceum)
in the undergrowth interspersed with heather shrublands between.
Openings are composed of pink mountain-heather (Phyllodoce empetriformis),
and white mountain-heather (Cassiope mertensiana) and Cascade
blueberry (Vaccinium deliciosum). Drier areas are more woodland
or savanna-like, often with low shrubs, such as common juniper (Juniperus
communis), kinnikinnick (Arctostaphylos uva-ursi), low
whortleberries or grouseberries (Vaccinium myrtillus or V. scoparium)
or beargrass (Xerophyllum tenax) dominating the ground cover.
Wetland shrubs in the Subalpine Parkland habitat include bog-laurel
(Kalmia microphylla), Booth’s willow (Salix boothii),
undergreen willow (S. commutata), Sierran willow (S. eastwoodiae),
and blueberries (Vaccinium uliginosum or V. deliciosum).
Undergrowth in
drier areas may be dominated by pinegrass (Calamagrostis rubescens),
Geyer’s sedge (Carex geyeri), Ross’ sedge (C. rossii),
smooth woodrush (Luzula glabrata var. hitchcockii),
Drummond’s rush (Juncus drummondii), or short fescues (Festuca
viridula, F. brachyphylla, F. saximontana). Various sedges are
characteristic of wetland graminoid-dominated habitats: black (Carex
nigricans), Holm’s Rocky Mountain (C. scopulorum), Sitka (C.
aquatilis var. dives) and Northwest Territory (C. utriculatia)
sedges. Tufted hairgrass (Deschampsia caespitosa) is characteristic of
subalpine wetlands. The remaining flora of this habitat is diverse and
complex. The following herbaceous broadleaf plants are important indicators of
differences in the habitat: American bistort (Polygonum bistortoides),
American false hellebore (Veratrum viride), fringe leaf cinquefoil
(Potentilla flabellifolia), marsh marigolds (Caltha leptosepala),
avalanche lily (Erythronium montanum), partridgefoot (Luetkea
pectinata), Sitka valerian (Valeriana sitchensis), subalpine lupine
(Lupinus arcticus ssp. subalpinus), and alpine aster (Aster
alpigenus). Showy sedge (Carex spectabilis) is also locally abundant.
Other Classifications and Key References. This habitat is called
the Hudsonian Zone,155 Parkland
subzone,134 meadow-forest
mosaic,74 upper subalpine zone,88
Meadows and Park, and Subalpine
Parkland.20 Quigley and
Arbelbide181 called this habitat Whitebark pine and
Whitebark pine-Subalpine larch cover types. Kuchler136
included this within the subalpine fir-mountain hemlock forest.
The Oregon Gap II Project126 and Oregon Vegetation
Landscape-Level Cover Types127 that would represent
this type are whitebark-lodgepole pine montane forest and subalpine parkland.
Additional references describe this habitat.11, 49, 75, 105, 112, 114,
115, 139, 144, 221
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Natural Disturbance Regime. Although fire is rare to infrequent
in this habitat, it plays an important role, particularly in drier
environments. Whitebark pine woodland fire intervals varied from
50 to 300 years before 1900. Mountain hemlock parkland fire reccurrence
is 400- 800 years. Wind blasting by ice and snow crystals is a critical
factor in these woodlands and establishes the higher limits of the
habitat. Periodic shifts in climatic factors, such as drought, snowpack
depth, or snow duration either allow tree invasions into meadows
and shrublands or eliminate or retard tree growth. Volcanic activity
plays a long-term role in establishing this habitat. Wetlands are
usually seasonally or perennially flooded by snowmelt and springs,
or by subirrigation.
Succession and Stand Dynamics. Succession in this
habitat occurs through a complex set of relationships between vegetation
response to climatic shifts and catastrophic disturbance, and plant species
interactions and site modification that create microsites. A typical succession
of subalpine trees into meadows or shrublands begins with the invasion of a
single tree, subalpine fir and mountain hemlock in the wetter climates and
whitebark pine and subalpine larch in drier climates. If the environment allows,
tree density slowly increases (over decades to centuries) through seedlings or
branch layering by subalpine fir. The tree patches or individual trees change
the local environment and create microsites for shade-tolerant trees, Pacific
silver fir in wetter areas, and subalpine fir and Engelmann spruce in drier
areas. Whitebark pine, an early invading tree, is dispersed long distances by
Clark’s nutcrackers and shorter distances by mammals. Most other tree
species are wind dispersed.
Effects of Management and Anthropogenic Impacts. Fire suppression
has contributed to change in habitat structure and functions. For
example, the current “average” whitebark pine stand will
burn every 3,000 years or longer because of fire suppression. Blister
rust, an introduced pathogen, is increasing whitebark pine mortality
in these woodlands.4 Even limited logging
can have prolonged effects because of slow invasion rates of trees.
This is particularly important on drier sites and in subalpine larch
stands. During wet cycles, fire suppression can lead to tree islands
coalescing and the conversion of parklands into a more closed forest
habitat. Parkland conditions can displace alpine conditions through
tree invasions. Livestock use and heavy horse or foot traffic can
lead to trampling and soil compaction. Slow growth in this habitat
prevents rapid recovery.
Status and Trends. This habitat is
generally stable with local changes to particular tree variants. Whitebark pine
is maybe declining because of the effects of blister rust or fire suppression
that leads to conversion of parklands to more closed forest. Global climate
warming will likely have an amplified effect throughout this habitat. Less than
10% of Pacific Northwest subalpine parkland community types listed in the
National Vegetation Classification are considered imperiled.10
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