Neighboring edges: interacting edge effects of linear disturbances on vegetation in treed fens

The influence of edges on forest biodiversity is an important environmental effect associated with habitat fragmentation, as edge effects can further reduce the remaining 'interior' habitat. However, extrapolating the influence of edges across the broader landscape has been difficult, especially regarding how to treat multiple edges in close proximity, where edge effects might interact. In this study, we examined the interaction of edge effects for multiple edges from a dense network of narrow (3-8 m wide) and low-severity linear disturbances called 'seismic lines'. Seismic lines are created during oil and gas exploration and are responsible for severe dissection of boreal forests in western Canada. Specifically, our objectives were to: (1) to compare the edge influence of "wide" (~8 m) and "narrow" (~3 m) seismic lines; and (2) to determine whether edges in close proximity show interaction of edge influences, i.e. do multiple narrow seismic lines have a stronger or weaker edge influence than a single narrow seismic line. We sampled vegetation along transects perpendicular to seismic lines in treed moderate-rich and poor fens. We used randomization tests of edge influence to calculate the magnitude and distance of edge effects. In moderate-rich fens, we found a positive edge influence on understory diversity from both wide and narrow seismic lines. We also found a weakening edge interaction on diversity, i.e., single narrow seismic lines had a stronger edge influence on diversity than multiple narrow seismic lines. In treed poor fens, multiple narrow seismic lines had a negative edge effect on tree density, understory abundance, richness, and composition. In addition, we found strengthening edge interactions in treed poor fens on tree density, graminoid cover, and understory composition. Our results show how assessing the edge influence of multiple disturbances can provide a better understanding of the cumulative effects of habitat fragmentation.Linetype is for the three different treatments (F2D = single wide treatment, F3D = single narrow treatment, L3D = multiple narrow treatment) and their corresponding edge aspect (S = south-facing edge). Plots SLA and SLB are the 2 seismic line plots Ecosite: PF = poor fen, MRF = moderate-rich fen. SL.width = seismic line width.Data was collected in poor and moderate-rich treed fens in Northern Alberta (S. of Fort McMurray)