The ecology of alvar vegetation in Canada: Description, patterns, competition.

Abstract

My research focused on (1) describing the vegetation of Canadian alvars, (2) examining ecological patterns in this system and (3) measuring the intensity of plant competition which occurs there. In chapter 1, ordination and classification techniques were used to describe alvar vegetation at two scales: local (within one alvar) and regional (among 4 alvar sites). At the local scale, changes in species composition corresponded to changes in soil depth and biomass. At the regional scale species composition was related primarily to geographic location--the southern site was distinct from the eastern and northern sites. Relationships between species distributions and soil depth and biomass could also be detected at this scale. In chapter 2, I examined the empirical relationships among important alvar state variables (soil depth, biomass and species richness) in order to test the predictions of the species richness model (forwarded by Grime and others) in a low biomass terrestrial system, and compare the pattern among 4 alvar sites. At all sites biomass was positively correlated with soil depth, suggesting that the soil depth gradient represents a gradient of increasing below-ground resources and decreasing above-ground resources. At each alvar, species richness varied curvilinearly with both biomass and soil depth; maximum species richness occurred at intermediate levels of these factors, as predicted by species richness models. However, the predicted decline in species richness at higher levels of biomass or soil depth was evident at only one site. In chapter 3, I present the results of a field experiment which measured the intensity of total, root and shoot competition along the gradient of soil depth at one alvar. Over all sites, the intensities of total and root competition were greater than zero; that of shoot competition was not. I suggest a model which relates the various effects of competition and of mutualism to the biomass range of interest. (Abstract shortened by UMI.)