Comparison of edge effects from well pads and industrial roads on mixed upland boreal forest vegetation in Alberta

The industrial footprint of oil and gas extraction in Alberta, Canada dissects the landscape in a network of linear and polygonal disturbances such as roads and well pads. The changes to biotic and abiotic factors beyond the boundaries of these disturbances into the adjacent ecosystem are called edge effects. A common assumption is that edge effects are proportional to the width of the disturbance, with wider disturbances leading to deeper effects into the forest. The objective of this study is to compare edge effects on plant composition, seed dispersal distance, seed weight, and microclimate across three disturbance types: narrow (< 20 m) and wide (> 20 m) roads, and well pads (> 100 m; 1.9 ha) in upland boreal forests in the oil sands region of north-eastern Alberta. We sampled 1 m² plots at six distances (0 m, 10 m, 15 m, 25 m, 50 m, and 75 m) along transects running perpendicular from the disturbance edge into the forest. Edge effects for plant communities were contained at the disturbance edge for all disturbance types considered. Understory species richness was lower at the disturbance edge and was dominated by introduced species and species with lighter seeds and with medium-distance dispersal mechanisms. Disturbance edges were characterized as having higher soil moisture content, higher soil temperature, and a thinner organic matter layer compared to the forest interior (> 10 m). With no effect of disturbance width on width of edge effects, our study does not support the assumption that narrower disturbances will necessarily result in narrower edge effects for vegetation and abiotic metrics.