The Biome: Subalpine to Alpine
The alpine lifezone or biome is most often described as the area above or near treeline on mountaintops. In the North Cascades, the elevation range of the alpine zone is from about 6,400ft to about 8,530ft (Douglas & Bliss, 1977). The subalpine biome often shares many characteristics with alpine plant and animal communities as the boundaries between the two lifezones are rather indistinct (Billings, 1974). The varying topography blends these two biomes, making the assignment of plant communities highly subjective. Among the main features that designate an area as subalpine are the discontinuation of the forest and the formation of “scattered tree clumps in a meadow mosaic” (Taylor & Douglas, 1995, p.4). These tree clumps are pioneers in harsh soil and growth conditions and “are normally short, with spreading branches, but [they still] retain definite crowns and do not develop the dense, low, thicketlike growth form known as krummholz” (Taylor & Douglas, 1995, p. 5-6). Krummholz is generally found on higher slopes and marks the beginning of the alpine zone (Taylor & Douglas, 1995). It would be much easier to assign general characteristics to these biomes if the mountain were flat ground with consistent weather patterns. However, nature provides large doses of interest and variety in vegetation patterns through vastly different slope aspects, substrate conditions, and extreme daily ranges in temperature, wind speeds, solar radiation, and water availability.
The combination of these abiotic factors creates many different habitats with microclimates and vegetation stripe communities occurring within those habitats. Fellfields are most common in the alpine biome, and are “characterized by rocky ground and dry soil, and are typically less than half covered by vegetation…Plants that grow here must be short in stature or they will be desiccated by freezing wind in winter and blasted by wind-driven sand in summer” (Visalli, 2014b, p.3). The constant frost action and avalanche potential acting on the slopes causes the soil to be unstable, poorly developed, and easily eroded as well, and pioneering plants must act quickly to establish roots when possible (Douglas & Bliss, 1977). Vegetation stripes can occur in the talus and scree slopes of fell- and boulder-fields, where soil and moisture has found a path of least resistance to percolate through or flow down and created a pocket of nutrients for plants to capitalize on (Douglas & Bliss, 1977).