Structure and composition of edges next to regenerating clear-cuts in mixed-wood boreal forest

Abstract

Abstract. We investigated the spatial and temporal pattern of edge influence on primary (forest structure) and secondary (understory structure and composition) responses at forest edges next to regenerating clear-cuts in Populus-dominated boreal forest in Alberta, Canada. We used before/after-harvest comparisons to determine whether there were significant effects of edge creation in the first and second year after harvest. We also investigated 5- and 16-yr-old edges to determine whether their structure and composition were significantly different from interior forest. Distance of edge influence (20–60 m) was not extensive compared to findings from studies conducted in other forest types. In the first two years after harvest, there were significant primary responses to edge creation including increased tree mortality, snag breakage and amount of downed coarse woody debris; as well as secondary responses including prolific vegetative regeneration of Populus spp. and a decrease in total shrub cover. Significant edge effects were still detectable 5 and 16 yr after edge creation, despite the rapid regeneration of Populus- dominated forest in the adjacent clear-cuts. These older edges showed evidence of past primary and secondary responses, including a more heterogeneous canopy, along with additional changes in under- story composition. At both younger and older edges the distance of edge influence was greater for secondary responses (up to 60 m) than for primary responses (10–20 m). We hypothesize that secondary responses to edge creation start later than primary responses and that the distance of edge influence is greater for secondary (vs. primary) responses.