AUTHORS: Yolanda F. Wiersma*, Memorial University of Newfoundland; R. Troy McMullin, Canadian Museum of Nature
ABSTRACT: Understanding how rare species are distributed across their range can be difficult due to heterogeneity between landscape units. We propose that lichen thalli along the trunk of a tree are analogous to habitat patches in a kilometers-extent landscape and hence can function as a model system. Applying the patch-mosaic model at smaller spatial extents allows for increased statistical power. We use this system to test whether landscapes with rare species are different from those without. We sampled macrolichen diversity along the trunk of 24 balsam fir trees in a stand on the Avalon Peninsula, Newfoundland, Canada, along with microclimate variables. We analysed difference in pattern by aspect and along the gradient of 1 m up the trunk as well as between trees containing a species of globally rare lichen vs. those that did not. We found no difference in total patch richness or abundance between the micro-landscapes. We found significantly consistent patterns in lichen patches along the trunk when we controlled for aspect and by aspect when we controlled for height up the tree. These patterns were similar on the trees with the rare species. Lichen species richness did not differ between trees containing the rare species vs. those that did not. Thus, lichen patch pattern is statistically similar between trees and, as such, these can be considered replicate landscape units and be used as model systems for observational and manipulative experiments to test questions about spatial pattern and process, such as those concerning distribution of rare species.
