This report summarizes an FIA-sponsored program with Louisiana-Pacific Canada Ltd. in 2008-09 that was focused on the impact of grass-seeded habitat on vole populations in forest plantations. The program is concerned with voles of the genus Microtus which are major mammalian pests in coniferous tree plantations in the Golden TSA. Voles feed on tree seedlings and saplings, particularly during winter months of peak years in abundance. This damage may result in direct mortality from girdling and clipping of tree stems or reduced growth of surviving trees which have sub-lethal injuries. In terms of conservation and sustainability of temperate forests, this feeding damage may limit regeneration of appropriate tree species in certain forest ecosystems. In addition, this damage increases the cost to reforest these stands in time for Free Growing Status, decreases net productive forested area, and results in loss of Mean Annual Increment. Feeding damage appears to be associated with high populations of voles in early successional habitats that develop after clearcut harvesting. The problem is widespread throughout the southern and central interior of B.C.
The 2008-09 project was designed to (1) determine the distribution and seasonal fluctuation of voles in relation to grass-seeded and non-grass-seeded areas in forest plantations; (2) assess the incidence of feeding damage by voles to plantation trees and its relationship to grass habitat; and (3) relate vole population data to grass habitat and other vegetation over a range of plantations and site characteristics, and develop a ?third approximation? of a forecast model of when and where voles will be a problem. Additional objectives from the Forest Science Program (FSP Y092081) were: (4) continue long-term monitoring of vole populations from the time of clearcut harvesting, and (5) compare vole populations in clearcut versus variable retention harvested sites to determine the influence of silvicultural system on habitat and population dynamics of voles.
Project areas were located on 7 units at Glenogle Creek and Roth Creek, ca. 25 km east of Golden, and covered a range of harvesting ages, systems, and sites. Units were selected to provide a range of grass habitat conditions on landings, skid trails, and roadsides to assist in developing phase 3 of a forecast model of when and where vole populations will be a problem in plantations. Long-term monitoring units are 821-58 (grid C), 825-1 (grid D), 825-6 (grid E), and 821-2 (grid F). All sites were selected on the basis of operational scale, reasonable proximity to one another, and have been monitored since the time of harvesting (2004). The variable retention (VR) units are located in habitats with residual Douglas-fir trees: 821-58 (grid J), 825-1 (grid K), and 825-3 (grid L). Clearcut (CC) units for comparison are those habitats without any retention of live overstory trees (grids C, D, and E).
There was a significant (r=0.46; P=0.01) positive relationship between numbers of long-tailed voles (Microtus longicaudus) on grids and percentage cover of grasses in the index-line survey (n=15) of plantation units. This pattern was also observed for percentage cover of total herbs, but the trend only approached significance (r=0.33; P=0.07). Similarly, mean numbers of long-tailed voles on grids were consistently higher (1.5 to 2.6 times) in grass than non-grass habitats during 2005 and early 2006, and were 1.4 to 3.7 times higher in 2008 . Mean crown volume index (m3/0.01 ha) of grasses was 3.67 in the grass habitats and 0.00 in the non-grass habitats in this analysis.
A third approximation of a forecast model and evaluation of grass habitats and other site characteristics for predicting vole damage to plantations was revised. Time since clearcut harvesting at 3-4 years in large contiguous units (from mountain pine beetle (MPB) salvage) seems to increase susceptibility to population buildups of voles and subsequent damage to plantatio ...