Forest Investment Account (FIA) - Forest Science Program
FIA Project Y092081

    Influence of Forest Harvesting and Succession on Vole Populations and Feeding Damage to Plantations
Project lead: Sullivan, Thomas (University of British Columbia)
Author: Sullivan, Thomas P.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
The problem of feeding damage to forest and agricultural crops by herbivorous small mammals has a long history in temperate and boreal ecosystems of North America and Eurasia. In forestry, voles of the genera Microtus and Clethrionomys are considered the major mammalian species affecting coniferous and deciduous tree plantations in North America. Populations of some species of voles tend to have cyclic fluctuations in abundance in northern latitudes with a peak every 3 to 5 years, although these periods may be interspersed with annual fluctuations in abundance. It is primarily during overwinter periods when high populations of these microtines feed on plantation trees. Voles feed on bark, vascular tissues (phloem and cambium), and sometimes roots of trees. Direct mortality may result from girdling and clipping of tree stems. Planted trees, with their nursery fertilization regime and enhanced palatability and nutrition, are nearly always preferred by voles over wildlings arising from natural regeneration. In terms of conservation and sustainability of temperate forests, feeding damage may limit regeneration of appropriate tree species in certain forest ecosystems, become costly to reforest these stands in time for Free Growing Status, decrease net productive forested area, and result in loss of Mean Annual Increment.
Abundance of Microtus populations and degree of damage is usually highest in early successional habitats that develop after forest harvesting by clearcutting, wildfires, and in old fields (perennial grasslands) undergoing afforestation. Grasses, herbs, and shrubs in these habitats provide food and cover for Microtus voles. Three species of Microtus, the long-tailed vole (M. longicaudus), the meadow vole (M. pennsylvanicus), and the montane vole (M. montanus) are implicated as major consumers of tree seedlings. A fourth species, the heather vole (Phenacomys intermedius) is also present in these small mammal communities but exists at low abundance (< 5 animals/ha). In addition, populations of the southern red-backed vole (Clethrionomys gapperi) occur primarily in mature stands of timber but may spill over into recently cut areas for 1-2 years after harvest.
Because of these habitat preferences, Microtus occur frequently on forested areas harvested by clearcutting, up to almost 10 years after logging. The red-backed vole may be present for 1 - 2 years after clearcut logging, but persists in small patch-cuts and potentially within the understory of snags, whether created by wildfire or attack by mountain pine beetle (MPB). There has been much research on the importance of habitat heterogeneity in population dynamics of small mammals. Clearcutting of forests yields relatively homogeneous early-successional habitats. Alternative harvesting practices such as group seed-tree and shelterwood systems produce heterogeneous habitat patterns compared with clearcutting. The habitat preferences of Microtus and red-backed voles likely vary over this range of harvesting practices in terms of mean abundance and response to habitat variables. Microtus spp. appear to be inversely related and C. gapperi positively related to basal area of residual trees.
To date, severe feeding damage by voles has been reported to seedlings planted on large (> 100 ha) contiguous openings created by harvesting (e.g., near Golden, Summerland, Invermere, Quesnel, Houston) or wildfire (e.g., Silver Creek Fire, Salmon Arm; and several locations in the southern interior after wildfires in 2003). However, the population fluctuations of Microtus are generally unknown in these areas, and it appears that vole populations may be high on some sites every year. In addition, comparisons of vole populations in clearcut and variable retention harvested sites have not been done.
The monitoring part of this proposal is a continuation of FSP project Y073138 which was initiated in 2004, and continued through to 2006, with three installations to follow population fluctuations of the four species of voles in the study east of Golden (Louisiana-Pacific Canada Ltd.). Monitoring from the time of clearcutting has been conducted from June to September 2004, and May to September 2005 and 2006, yielding 16 monthly datasets for analysis. Long-tailed vole populations have been increasing each year since the clearcut harvesting.
We are continuing to monitor vole populations on these sites from 2007 to 2009, by which time populations should start declining. In addition, we have initiated in 2007 a comparison of vole populations in clearcut versus variable retention harvested sites to determine the influence of silvicultural system on habitat, population dynamics of voles, and feding damage to seedlings.
Related projects:  FSP_Y081081FSP_Y103081


Executive summary (16Kb)

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Updated August 16, 2010 

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