The Three Sisters Wilderness Area is a UNESCO Biosphere Reserve representing the northern half of the Sierra-Cascade Province. It encompasses nearly 100,000 ha of largely undisturbed landscape straddling the crest of the central Cascade Range in Oregon. The Three Sisters was given wilderness status in 1957 and selected as a Biosphere Reserve in 1974 to represent a "control" area for the nearby H. J. Andrews Experimental Forest Biosphere Reserve. Coniferous forests dominate the reserve, although it supports a diversity of non-forest habitats, including montane and subalpine meadows. Integral to the establishment of a Biosphere Reserve is the collection of baseline data on the composition, structure, and distribution of its major plant communities. These baseline data are essential to monitoring both natural vegetation change and changes attributable to human activities. At the time this study was initiated (1981), basic ecological research in the Three Sisters had been limited. The goals of this study were two-fold: (1) to undertake a phytosociological analysis of the diversity of forest and non-forest plant communities and their relationships to the physical environment; and (2) to assess historical and ongoing changes in vegetation across natural forest-meadow boundaries (or ecotones). Studies addressing this second goal included a retrospective analysis of historical patterns of tree invasion as they relate to site environment, grazing history, and climate; and an analysis of subsequent changes in vegetation (1983-2009) including both tree and ground-layer communities.
Bradley G. Smith, Charles B. Halpern, Eric A. Miller, Jerry F. Franklin, Ryan D. Haugo
Our objectives were five-fold:
- 1. To describe the composition, structure, and distribution of forest and meadow communities in the Three Sisters Wilderness Area/Biosphere Reserve, and to develop a classification of community types
- 2. To relate community patterns to environmental variation
- 3. To characterize the fire history of these forests
- 4. To characterize spatial and temporal patterns of tree invasion into montane and subalpine meadows and their biotic and abiotic controls (grazing history, climate, and site environment)
- 5. To provide a system of permanent transects to monitor future changes in the composition and structure of forest-meadow boundaries