Sunday, 9 February 2003
Investigating Vegetation Changes in Relation to Altitude and Environmental Factors Along Oliver and Clear Creeks in the Cloud Peak Wilderness Area of the Big Horn Mountains
In July 2002, the Cloud Peak Wilderness Area of the Big Horn Mountains in Wyoming was the site of a vegetation study conducted by an international team of U.S. and Scottish students. The study examined the change in vegetation across various altitudes within the Oliver/Clear Creek watershed. At each altitude site, a N-S transect was set up across the creek or, in one case, a moraine crest. Flags were then placed every 10 m, from the side of the creek, out to 40 m, and, at each flag, 1 m2 quadrats were laid out. The ground cover at each quadrat was analyzed through the use of the point-intercept method that utilized knitting needles on a meter stick frame. The vegetative species selected were then identified and recorded along with other types of cover to allow for the calculation of ground cover percentages. Soil samples were also taken at each site and are being tested for various micro and macronutrients, along with conductivity and pH. Percent overhead cover, slope angle, and girths of the five nearest trees were additionally recorded at each quadrat. At the riparian sites, benthic macroinvertebrates were observed so as to ascertain the water quality of the stream through Pollution Tolerance Index calculations; rock length was also measured so as to determine the substrate size of the stream. The atmospheric temperature and amount of rainfall along with other atmospheric conditions were recorded throughout the three week period. Site characteristics did, at times, necessitate the modification of study methods.
Several changes in vegetative characteristics due to altitude were noted. There was a clear progression of plant species from the low to high elevation sites; only two plant types were found at all elevations and the plant species of the highest elevation are almost completely distinct from those at the lowest elevation. Twenty-nine species were restricted to a single altitude site. Forb percentages were lowest at the lowest elevation site and highest at the highest elevation site. The greatest species richness was observed in the two middle altitude transition sites, where species from both high and low altitudes were recorded. At each altitude site, litter and rock cover were found to be higher on steeper slopes; at each riparian altitude site, forb cover predictably decreased with greater distance from the stream. The macroinvertebrate data indicated that the Oliver/Clear Creek watershed area is of good to fair quality throughout the study area and that the substrate size ranged from cobble to boulder. Additional data from the soil analyses will aid in the interpretation of the vegetation distributions at the studied altitudes.