VOLE POPULATION MONITORING AND
PROTECTION OF NEW PLANTATIONS

Several species of voles (genera Microtus and Clethrionomys) have been identified as mammals which inflict feeding damage to coniferous seedlings in young plantations in temperate and boreal forests. These herbivorous rodents feed on the bark, vascular tissues, and sometimes roots of trees, particularly during winter months when alternative foods are limited. Vole damage may result in direct mortality from girdling and clipping of tree stems or reduced growth from sublethal injuries. In terms of conservation and sustainability of temperate forests, feeding damage may limit regeneration of appropriate tree species in certain forest ecosystems. Feeding damage appears to be associated with high populations of Microtus spp. in early-successional habitats that develop after harvesting or wildfire. Such habitats are composed of herb (particularly grasses) and shrub species which provide food and cover for voles. Some Microtus populations tend to have cyclic fluctuations in northern latitudes with a peak every 3 to 5 years, although these periods may be interspersed with annual fluctuations in abundance. The southern red-backed vole (C. gapperi) occupies primarily mature and old-growth forests.

Because of these habitat preferences, Microtus occur frequently on forested areas harvested by clearcutting, up to almost 10 years after logging . Conversely, the red-backed vole appears to decline in abundance within 1 or 2 years after clearcut logging in western North America. There has been much research on the importance of habitat heterogeneity in population dynamics of small mammals . Clearcutting of forests, wildfires, and large-scale salvage of stands infested with mountain pine beetle yield relatively homogeneous early-successional habitats. Alternative harvesting practices such as group seed-tree and patch-cutting systems produce heterogeneous habitat patterns compared with clearcutting. To date, high vole populations and severe feeding damage to seedlings planted on large (> 100 ha) openings have been reported throughout the southern and central interior of BC. It is likely that there is a synchronous and predictable pattern to these vole outbreaks across a wide geographic range.

For more information contact:
Thomas P. Sullivan
Dept. of Forest Sciences
University of BC
Tom.sullivan@ubc.ca