Spatial and temporal distribution and abundance of butterflies in the Andrews Experimental Forest

Objectives: To detect patterns in the distribution and abundance of butterfly species in time and space across various plant communities within the entire HJA Forest watershed for multiple years. Abstract: The distribution and abundance of butterfly species on the Andrews Forest is strongly influenced by geographical scale, elevation, aspect, plant community, management regime, and time of year. Patterns of distribution and abundance are based on an historical total of 80 species, of which 73 are resident species and about 55 of which may be observed in any given year. Butterflies were surveyed at two- week intervals from late April through early October over a three-year period (1994-6). Approximately one-third of the watershed was covered during each visit, thus each area was sampled at about 6 week intervals within each sample season. Temporally the highest number of species occur as adults during the last two weeks of June. Spatially the HJA Forest can be divided into 13 distinct zones. Each zone is unique based on the assemblage of butterfly species. The upper elevation ridge-top zones contained the highest number of species (n = 44 to 51) and the headquarter area and lower elevation Blue River Ridge zones contained the lowest number of species (n = 29 to 33). Each of the 13 zones lacks about 25 of the 73 resident butterfly species, suggesting that heterogeneity of the landscape is important. Each species was categorized into one of eight biogeographical distributions based on the regional patterns of the species (or subspecies) range throughout western North America. Great Basin and Californian species were represented in addition to typical west-slope Cascadian species. Some butterflies, therefore, appear to be at the northern or western limit of their distribution on the HJA. Mature forest, clearcut and meadow habitats were shown to differ greatly in butterfly richness and abundance. The presence of roads increased species richness and abundance in butterfly-poor forests and clearcuts, but had no affect upon the already butterfly-rich fauna of subalpine meadows. The species-rich locations within the Andrews Forest were characterized by a south to west aspect (high solar radiation), an open, meadow or “rock garden” habitat, locally high plant species richness, and an elevation greater than 4000 feet