Predation in heterogeneous forests: A comparison at natural and anthropogenic edges

Abstract

The boreal mixed-wood forest is a naturally heterogenous system that has an extensive amount of forest edge. Recent increases in timber harvesting as well as oil and gas exploration have imposed an abundance of anthropogenic forest edges across this landscape. Because past research has indicated that songbirds nesting near forest edges can suffer increased nest predation, we conducted an artificial nest experiment to compare predation pressure on songbird populations along natural and anthropogenic edges. Artificial nests were placed in shrubs and on the ground in aspen stands adjacent to: (i) white spruce stands, (ii) clearcuts, (iii) seismic lines, and, (iv) in the interior of aspen stands. In 1995, predation on shrub nests was higher at aspen/seismic line edges, whereas in 1996 it was higher at aspen/white spruce edges. In both years, predation on ground nests was not significantly different among sites. We also examined vegetation at the nest, stand, and landscape scale to determine if these factors affected the probability of predation. Vegetation was not a strong or consistent predictor of predation events at these scales. Predation tended to be higher where there was preferred habitat for nest predators such as red squirrels (Tamiasciurus hudsonius). We encountered a large degree of temporal and spatial variation with this study and we emphasize the importance of long-term studies to separate true effects from stochastic processes. In the short term, the creation of anthropogenic edges in the boreal mixed-wood forest does not appear to cause any relative increase in predator pressure on artificial nests when compared with natural edges or the forest interior.