King County subalpine and alpine habitat

Mountain goats are commonly found in alpine habitat. Photo by Jennifer Vanderhoof.
Mountain goats are commonly found in alpine habitat. Photo by Jennifer Vanderhoof.

Except for a very small area in the SE corner of the County, the subalpine and alpine habitats are located in the North Cascades Ecoregion that occupies the NE quarter of King County. This ecoregion is composed of steeply dissected valleys that rise precipitously to the subalpine (montane) forests, meadows, and parklands and, in a short distance more, to the alpine ridges and peaks of the Cascade Crest. The habitats that typify this high-elevation zone are among the most undisturbed habitats remaining in King County.

For the purposes of this discussion, we separate the subalpine zone into three distinctive habitats: the montane forest, the subalpine parkland, and the subalpine meadow. The montane forest zone is characteristically an unbroken forest of mountain hemlock with isolated trees of Alaska cedar and Pacific Silver fir; however, on the western slopes of  King County’s mountains, the forests with Pacific Silver fir typically transitions directly into the subalpine parkland without passing through a hemlock forest. The Montane forest is the coolest and wettest of the forested zones in the Pacific Northwest. Annual precipitation is 163 to 284 centimeters (64 to 112 inches); snowfall is heavy (406 to 1,270 centimeters; 160 to 500 inches), with a snowpack up to 6.4 meters (21 feet) deep that persists into late summer. The dominant species, mountain hemlock, is a large tree for this elevation (1677 meters, 5,500 feet, and higher). It matures to 500 - 700 years of age and can be 38 meters (125 feet) tall and up to 2 meters (80 inches) in diameter. Understory plants in these hemlock forests will include mountain huckleberry, mountain rhododendron, and bear grass (which is actually in the lily family). Bear grass is a tall plant with a spectacular creamy white bloom, which supports communities of insects in the spring. Typical animals of the montane zone are elk, black bear, cougar, and deer, all of which migrate here in summer for food and to breed and descend in winter to avoid snowpack.

At the upper elevational limit of the montane zone, mountain hemlock forest gives way to the parkland zone, a habitat of shrub-herb meadows dotted with isolated patches of trees. In King County, this parkland habitat dominates the landscape just west of the mountain crest from Snoqualmie Pass all the way to Snohomish County to the north (continuing all the way to Canada). Southward, this habitat type does not appear again until Mt. Rainier. Many ecologists familiar with the mountains of the world contend that this parkland habitat is unique on the planet, both for its extent and for its deep (gradual) transition between forest and open meadow. The shrub-herb layer of this habitat is mainly a blend of three species of New World heathers and a dwarf shrub, mountain huckleberry; the tree islands generally consist of three conifers: mountain hemlock, subalpine fir, and Alaska cedar. Notably, this habitat is far from static and may even be somewhat transient, an accident of recent climatic history. In the early 1900s, subalpine fir and mountain hemlock began to invade the meadows, reaching a peak in the 1930s before dying back. Most alpine ecologists believe that a warmer, drier period from about the 1880s through the early 1930s promoted the invasion. Now, only scattered saplings, bleached and wind-worn, remain to remind us of this dramatic advance and retreat of vegetation. This invasion could occur again with warming trends attributable to climate change, and it may persist for far longer than the 40 - 50 years of the last invasion.

At slightly higher elevations, especially on the windward faces of this zone, even the small islands of trees are no match for the conditions, and the open meadow zone dominates the slopes. Again, heathers and mountain huckleberry may be the dominant ground cover, but in spring some meadows bloom with glacier lily (Erythronium grandiflorum[1]), avalanche lily (E. montanum), and springbeauty. Later in the summer, these same meadows boast white pasqueflower, mountain artemesias, alpine bistorts, and paintbrush. In the persistent snowy places of these meadows, the black alpine sedge forms tenuous communities that appear and disappear from year to year. Among the boulders and talus slopes of these meadows are the dens of yellow-bellied and hoary marmots, mammals and the only full time residents of this habitat.

Above the timberline that marks the upper limit of the subalpine zone lies the alpine zone of the Cascades, a habitat of such severity that no trees can persist. The line that demarcates subalpine from alpine is often populated by krummholz, the species-nonspecific name for the dwarfed conifers that sprawl along the ground in the direction of the prevailing winds. In King County, the alpine zone is characterized by many low-growing herbs that extend upward from the subalpine zone: Alaska spirea (Luetkea pectinata), mountain heliotrope (Valeriana sitchensis), and the black sedge (Carex nigricans) are common. A few other shrubby species also may be found here: common juniper, shrubby cinquefoil, kinnikinnik, and snow willow (Salix nivalis). This last species, with its prostrate growth habit, is often a surprise in the alpine and its remarkable growth habit is more characteristic of willows commonly found in the far north. Nevertheless, this habit is not merely a growth variation within a species; snow willow is truly distinct species. In general, the species that characterize the alpine habitat of King County tend to be shared with the upper limits of the subalpine.

[1] Scientific names are used when common names may cause confusion or misidentification.


About the Author: 
Robert Fuerstenberg, Jennifer Vanderhoof, Jonathan Frodge, Kathryn Gellenbeck, Kollin Higgins, Klaus Richter, and Kim Stark collaborated to write the King County Biodiversity Report, which was published by the King County Department of Natural Resources and Parks as part of the Local Action for Biodiversity (LAB) project, a global biodiversity initiative. The report serves as the foundation of a plan for long-term protection of biodiversity in King County. Citation: King County. 2007. King County biodiversity report. King County Water and Land Resources Division, Department of Natural Resources and Parks. Prepared for International Council for Local Environmental Initiatives (ICLEI), Biodiversity Initiative. 102 pp.