Vole-feeding damage and forest plantation protection: Large-scale application of diversionary food to reduce damage to newly planted trees

Forest and agricultural crops periodically experience feeding damage from herbivorous rodents such as voles of the genera Microtus and Clethrionomys. This problem has a long history, which needs a management solution that is both economically and ecologically viable. This study tested the hypothesis that large-scale (6–16 ha) application of diversionary food would reduce vole-feeding damage to newly planted trees. Four overwinter Experiments (A, B, C, and D) were conducted with long-tailed vole (Microtus longicaudus) populations in new forest plantations of lodgepole pine (Pinus contorta), Douglas-fir (Pseudotsuga menziesii), and interior spruce (Picea glauca×Picea engelmannii) near Golden, British Columbia, Canada, from 2003 to 2007. Diversionary food “pucks” were composed of Douglas-fir bark mulch and alfalfa (Medicago sylvatica) pellets/meal mixed with canola (Brassica rapa) oil and wax. Mean percentage (±SE) survival of trees was similar (P=0.18) between control (72.6±11.8) and food (86.2±8.7) sites in Experiment A. Experiment B had intensive feeding by voles and near exhaustion of the food supply in three of five replicates, with no statistical difference (P=0.11) between control and treatment sites. This pattern continued in Experiment C with total tree survival appearing highest (P=0.06) in the intermediate puck density. Mean (±SE) percentage survival of total trees was significantly (P=0.05) higher in food (85.0±6.3) than control (62.5±14.3) sites in Experiment D. Despite these variable results, in those experimental units with substantial feeding pressure by voles and a sufficient overwinter supply of diversionary food, tree survival was 20–25% higher in food than control sites. If food can help maintain sufficient trees on a site and it is required for only one or two winters, diversionary feeding may be an economical and ecological solution to this significant reforestation problem.