Edge dynamics in the cold-temperate deciduous forest of eastern Canada

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Edges are often characterized by processes with rates that differ from those typical of either type of adjacent ecosystems: higher rates - hyperdynamism; lower rates - hypodynamism. Three types of edge can be identified: an open edge is a recently-formed edge along which no change in forest structure has yet occurred; an edge closes with time as trees bordering the edge produce a denser canopy and as the shrub understory produces a denser foliage; an embedded edge develops with time as shrub and tree species are recruited at progressively greater distances into the adjacent old-field. Because edges differ in their nature, differences in process rates across edges may be more or less apparent. In this proposal, I want to determine how edge type affects the demographic processes of both forest and non-forest plant species. My general hypothesis is that edge effects on population processes depend on the nature of the edge: I suggest that open edges are those where differences in the rates of demographic processes are most significant, differences decreasing as edges become closed or embedded with time. I also propose that, among the different understory functional groups, spring-flowering ephemeral species are those that are less affected by edge type, spatial contrasts along edges in major environmental variables being more moderate in spring than in summer. Because environmental heterogeneity is typically greater across edges than in the 'interior' of either adjacent ecosystem, edges represent ideal systems to test the diversity-production relationship with regard to environmental heterogeneity. As open, closed and embedded edges differ in their characteristics, the significance of environmental heterogeneity for the diversity-production relationship can be tested using different types of edge. I suggest that open edges are those across which environmental heterogeneity is higher, with greater effects on the diversity-production relationship. This research has significant conservation implications as altered population dynamics near edges may lead to greater risks of extinction in highly fragmented landscapes.