FACTORS UNDERLYING VEGETATIVE COMMUNITY DISTRIBUTION IN A NORTHWEST MONTANA FEN

Ambrose fen in the Flathead valley of Northwestern MT displays an array of vegetative community types, including carr (peat shrubland), dwarf carr and spruce swamp forest. These communities are distributed in an array of stripes and islands, all growing on a large mat of waterlogged peat moss and peat-based soil. The observed heterogeneity in vegetation is of interest because it does not appear to be linked to differences in soil moisture or elevation, factors which often strongly influence plant distribution in the region. I hypothesized that alternate environmental factors such as soil pH, bulk density or nutrient content are instead responsible for determining the distribution of the plant communities. During the spring and summer of 2010 I collected data on these variables at 9 sites across the fen, including at least 2 sites from each main community type. In addition, I measured the water content (by percentage weight) of the soil at each site, to attempt to prove or disprove my null hypothesis that soil moisture was determining community distribution. I also quantified the relative abundance of each species present at each site using quadrat surveys. The abundance of vegetation (both as individual species and as groups – e.g. sedges) at each site was then correlated with each soil variable. No one variable explained the distribution of the plant communities in Ambrose fen, but a few interesting trends were observed. For example, increased soil solution conductivity (used as a proxy for levels of nutrient ions) was positively correlated with the percentage cover of shrubby species, with an R2 value of .694. This relationship warrants further investigation to determine its true strength and to attempt to locate the source of the differences between nutrient levels at the sites. Further, any connections between soil variables and plant distribution are potentially important for conservation because the fen contains several rare species whose preferred habitat may decline or vanish if these variables shift