Nest predation in and adjacent to cutblocks with variable tree retention

Abstract

Partial harvesting, or the retention of live trees in cutblocks, is thought to reduce the impacts of clearcutting on wildlife biodiversity. An unintended biproduct of this practice may be an increase in nest predation in and adjacent to these cutblocks. We examined patterns of predation on artificial ground and shrub nests in and adjacent to stands where varying amounts of trees were left after harvesting in Alberta’s boreal mixed-wood forest. We placed nests in old, aspen-dominated stands adjacent to 3-year-old cutblocks with high (86–133 trees/ha), intermediate (48–55 trees/ha), and low (10–36 trees/ha) residual tree retention, and in forested controls (246–414 trees/ha). In a second experiment, we placed nests in residual tree clumps in high and intermediate retention cutblocks and in forested controls. Each nest contained one painted plasticine and one Chinese Painted Quail ( Coturnix chinensis) egg and predators were identified based on marks left in plasticine eggs. Vegetation structure and composition and overhead and lateral cover were measured around each nest. Data were analysed with a nested logistic regression approach, using generalized linear models with quasi-likelihood functions to analyse nest predation with respect to treatment and vegetation characteristics around the nest. In both experiments the identified nest predators were murid rodents, red squirrels ( Tamiascurus hudsonicus) and birds. Nests closer to the ground were more likely to be depredated. Nest predation was not related to the level of residual tree retention in either experiment nor to the size of residual tree clumps in the second experiment. Vegetative cover at the nest did not enter explanatory models, nor did most measures of vegetation structure and composition around the nest. The few vegetation factors that did enter models were not consistent between experiments and generally the models had low predictive power. We conclude that, within 3 years postharvest, elevated nest predation did not occur in tree-retention cutblocks when compared to unharvested forests, nor in high (compared with low and intermediate) tree-retention cutblocks.