Forest structure and composition at fire edges of different ages: Evidence of persistent structural features on the landscape

Abstract

Boreal forest landscapes are dynamic with stands in different stages of development following stand-replacing disturbances such as fire and insect outbreaks. Forest edges are an important component of these heterogeneous landscapes but there have been few studies on intermediate-aged forest edges which are needed for a comprehensive perspective on the spatiotemporal dynamics of forest edges. We described the structure, composition and extent of edge influence at 13, 25 and 39-year old fire edges in black spruce boreal forest in northwestern Québec and northeastern Ontario to characterize their structural development and to assess effects of edge development on the understorey. Forest structure and understorey composition were sampled along transects perpendicular to edges of the fires. Edge influence was assessed using randomization tests. Black spruce forest was relatively unaffected by edge influence beyond 5m into the forest at all ages of edges studied. Edge influence on the understorey was weak and not extensive at intermediate-aged edges with few consistent responses of individual species. Less decayed snags and logs at 13 and 25-year old edges peaked in abundance at or near the edge with values higher than in either adjacent ecosystem. Overall, intermediate-aged fire edges in black spruce forest showed little evidence of further changes in canopy structure with time. Structural development of these edges as well as the regeneration of the disturbed areas also resulted in reduced edge influence on the understorey. A new insight from our study is that intermediate-aged forest edges may contribute unique structural features to landscapes such as a reservoir of deadwood that may be important for wildlife species.