QUANTIFICATION OF THE SPATIAL COOCCURRENCES OF ECOLOGICAL BOUNDARIES

In this paper, we investigate spatial relationships between vegetation boundaries and environmental boundaries from a second-growth forest i n southwestern Quebec, Canada. Four statistics that quantify the amoun t of direct spatial overlap and the mean minimum distance between boun daries are introduced and used to compute the degree of spatial co-occ urrences between boundaries. The significance of these statistics is d etermined using randomized and restricted permutation tests. Boundarie s based on tree species density are found to significantly overlap the locations of boundaries delineated by the environmental data at the s tudy site. Significant overlap is also found using boundaries defined by tree presence-absence data and environmental variables. Vegetation boundaries based on tree species density and on tree presence-absence data are not, however, at the same locations. This suggests that for t he study site the two types of vegetation boundaries (tree density and presence-absence) reflect different responses to underlying environme ntal processes. Vegetation boundaries determined using species diversi ty and species richness, although spatially related to the presence-ab sence boundaries, did not overlap the environmental boundaries. Result s of the two permutation tests (randomized and restricted) agree only when the spatial relationship between the two boundary types is strong . Overall, randomization is found to be a more conservative test for d etecting boundary spatial relationships, rejecting the null hypothesis of no spatial relationship fewer times than the restricted permutatio n test.