No. 9. Subalpine Parkland

Rex C. Crawford and 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 Owyhee Mountains, and Okanogan Highlands), extends into mountains of Canada and Alaska, and to the Sierra Nevada 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 typically accumulate. 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.

Composition. Species composition in this habitat varies with geography or local site conditions. The tree layer can be composed of 1 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 Cascades. Whitebark pine (P. albicaulis) is found primarily in the eastern Cascade mountains Okanogan Highlands, and Blue Mountains. Subalpine larch (Larix 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 undergrowth. 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 Arbelbide ¹⁸¹ called this habitat Whitebark pine and Whitebark pine-Subalpine larch cover types. Kuchler ¹³⁶ included this within the subalpine fir-mountain hemlock forest. The Oregon Gap II Project ¹²⁶ and Oregon Vegetation Landscape-Level Cover Types ¹²⁷ 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}.

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 reoccurrence 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 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.