The specific goals of our research were:
Plant Association Classification and Environmental Relationships of Forest and Meadow Communities:
See Halpern et al. (1984) for a complete description of methods. Sampling of forest sites was conducted during summer 1981 and meadow sites during summer 1982 using the reconnaissance method of Franklin et al. (1970, A reconnaissance method for forest site classification. Shinrin Richi XII (1): 1-14). The term "meadow" is applied broadly to a diversity of non-forested vegetation types, including mires, lithosolic ridgetop. Sampling of forest vegetation was restricted to the Separation Creek drainage, located centrally on the west side of the Cascade crest. Sampling of meadow vegetation was more widespread covering most regions of the wilderness. Potential study sites were identified from topographic maps and aerial photographs. We sampled a total of 162 forest plots and 152 meadow plots (including montane and subalpine meadows). At each location, a circular plot (500 m2) was subjectively placed in visually homogenous vegetation. Compositional characteristics were recorded through estimates of projected canopy cover of each vascular plant species. Structural characteristics (in forest vegetation) were assessed through size classes distributions of trees and by tree age and height measurements. Environmental features such as elevation, slope, aspect, landform and topographic character were recorded. A soil pit was dug, particle size distribution determined, and a description of horizons and rooting depth noted. Depth to water table (if present) was noted in meadow plots. In forest plots, the ages of one or more dominant trees per plot were determined from increment cores. Detailed descriptions of analyses and results can be found in Halpern et al. (1984, Composition, structure, and distribution of the ecosystems of the Three Sisters Biosphere Reserve/Wilderness Area. Final Report to the USDA).
Details of the 1983 sampling methods are contained in Halpern et al. (1984) and of the 1993 methods in Miller (1995, The dynamics of forest-meadow ecotones in the Three Sisters Wilderness, Oregon: Variation across environmental gradients. M.S. thesis, University of Washington, Seattle) and Miller & Halpern (1998, Effects of environment and grazing disturbance on tree establishment in meadows of the central Cascade Range, Oregon, USA. Journal of Vegetation Science 9: 265-282). In 1983, 21 permanently marked transects were established across forest-meadow boundaries at 17 locations. Transect locations were chosen to encompass a range of physical environments and vegetation types, and to represent a diversity of tree invasion patterns. End points and intermediate points were marked with steel reinforcing bar. Transects were two meters wide (but were expanded in 1993, see below), and ranged in length from 50-150 m. Each transect began well within the forest and extended into the adjacent meadow beyond the extent of tree invasion. On alternating sides of the transect, 1 x 1 m plots were established 1-2 m apart for sampling vascular plant species abundance (cover and frequency). Five size classes were delineated for each tree species and each size class was assessed separately for cover.
In 1993, 15 of the original transects were resampled at which time each transect was widened to increase the sample size of trees. One transect was lengthened and two non-permanent transects were also added. Transects now vary in length from 50-150 m and in width from 5-30 m (a single transect is 2 m wide). As in 1983, elevation, slope, aspect, and topography were recorded and a set of soil pits was dug to assess soil texture and for hydric sites, the presence and relative depth of the water table. Similarly, to quantify the ground layer vegetation, the cover of all vascular plant species was visually estimated in a series of 1 x 1 m plots spaced 1-2 m apart on alternating sides of each transect. Trees were sampled in contiguous plots along both sides of each transect. Species, height, diameter (basal or breast-height), and position along the transect were recorded for each individual.
