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Wildfire, clearcutting, and vole populations: Balancing forest crop protection and biodiversity

Sullivan, Thomas P., Sullivan, Druscilla S.
Crop protection 2016 v.85 pp. 9-16
Microtus pennsylvanicus, Peromyscus maniculatus, Sorex, Tamias, clearcutting, forbs, forest habitats, forest litter, forests, grasses, growing season, herbaceous plants, herbs, plant protection, seedlings, small mammals, species diversity, spring, tree damage, tree mortality, trees, voles, wildfires, British Columbia
Early successional forest habitats that develop after wildfire may provide ideal conditions for population build-ups and subsequent fluctuations by Microtus voles. Regeneration of burned-over forest land may be hindered by consumption of planted trees by voles. A high abundance of voles, occurring in the second growing season after a wildfire, may result in serious feeding damage to seedlings leading to major plantation failures. A wildfire occurred near Golden, British Columbia, Canada in the spring of 2011 and may have initiated the successional conditions to generate a vole population outbreak with consequent feeding damage to tree seedlings. We tested the hypotheses (H) that (H1) abundance of herbaceous plants (grasses and forbs) will be greater, and (H2) abundance of voles and incidence of feeding damage to tree seedlings will be higher, in burned than unburned (control) sites. Microtus voles and other forest-floor small mammals were live-trapped for four years (2011–2014) in replicated sites of a wildfire (burned plantation), control (unburned) plantation, and a new control clearcut. Abundance of total herbs and grasses, incidence of feeding damage, and mortality to tree seedlings by voles were measured in all sites. Mean abundance of total herbs and grasses were similar among treatments during the post-wildfire period. Mean annual peak numbers of Microtus in clearcut sites ranged from 18 to 30 per index-line. Annual peak numbers in the burned and control plantation sites ranged from 5 to 8 voles per index-line and were essentially stable at these numbers. Vole populations in the control and burned plantation sites were dominated by the meadow vole (Microtus pennsylvanicus Ord), and those in the clearcut sites by the long-tailed vole (Microtus longicaudus Merriam). Mean mortality of trees was significantly higher in the control clearcut sites at 30% compared with 13% in the burned plantation sites. These results did not support either H1 or H2. Wildfire, at least in this case, did not generate high populations of voles and significant damage to tree seedlings. Mean abundance of total small mammals was similar in burned and control plantation sites, but less than in clearcut sites. Populations of the deer mouse (Peromyscus maniculatus Wagner) increased after wildfire and those of the southern red-backed vole (Myodes gapperi Vigors) declined. Populations of the northwestern chipmunk (Neotamias amoenus J.A. Allen) and Sorex spp. did not show a clear preference for any of the treatments. Disturbance by clearcutting or wildfire seemed to reduce species richness and diversity, but all eight species of small mammals were present in each of the treatments.