Nest predation in and adjacent to cutblocks with variable tree retention

Partial harvesting, or the retention of live trees in cutblocks, is thought to reduce the impacts of clearcutting on wildlife biodiversity. An uninten ded biproduct of this practice may be an increase in nest predation in and adjacent to these cutblocks. We examined patterns of predation on artificia l 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 cutbloc ks 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 tre es/ha). In a second experiment, we placed nests in residual tree clumps in high and intermediate retention cutblocks and in forested controls. Each ne st contained one painted plasticine and one Chinese Painted Quail (Coturnix chinensis) egg and predators were identified based on marks left in plasti cine eggs. Vegetation structure and composition and overhead and lateral co ver were measured around each nest. Data were analysed with a nested logist ic regression approach, using generalized linear models with quasi-likeliho od functions to analyse nest predation with respect to treatment and vegeta tion characteristics around the nest. In both experiments the identified ne st 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 experimen t. Vegetative cover at the nest did not enter explanatory models, nor did m ost measures of vegetation structure and composition around the nest. The f ew vegetation factors that did enter models were not consistent between exp eriments and generally the models had low predictive power. We conclude tha t, within 3 years postharvest, elevated nest predation did not occur in tre e-retention cutblocks when compared to unharvested forests, nor in high (co mpared with low and intermediate) tree-retention cutblocks. (C) 2000 Elsevi er Science B.V. All rights reserved.