Dynamics of montane and subalpine meadows in the Three Sisters Wilderness Area and Biosphere Reserve, 1981-1993

The Three Sisters Wilderness Area is a Biosphere Reserve that represents the northern half of the Sierra-Cascade Province. It encompasses nearly 100,000 ha of essentially undisturbed landscape straddling the crest of the central Cascade Range, Oregon. Coniferous forests dominate the Three Sisters, although the Wilderness also supports a diversity of non-forested habitats including montane and subalpine meadows. The Three Sisters was given wilderness status in 1957 and was selected as a UNESCO Biosphere Reserve in 1974, to represent a "control" area for the nearby H. J. Andrews Biosphere Reserve. Integral to the establishment of a Biosphere Reserve is the documentation of existing ecosystems with baseline data. However, basic ecological research in theThree Sisters has been relatively limited. We conducted two types of studies: (1) phytosociological studies to characterize current vegetation patterns and to interpret relationships between community composition and major environmental and edaphic gradients, and (2) retrospective analyses of the invasion of montane and subalpine meadows by trees with a focus on the effects of recent climatic variation, grazing history, and site environment.