Population fluctuations of meadow voles (Microtus pennsylvanicus) in a landscape with cumulative clearcutting

We investigated the responses of meadow vole (Microtus pennsylvanicus) populations to cumulative clearcutting of coniferous forests during four Periods over a 42-year span from 1979 to 2020 near Summerland, British Columbia, Canada. This vole is a common inhabitant of moist meadows, grasslands, and early successional sites after forest clearcutting and wildfire and may damage plantation trees on reforestation sites. We tested three hypotheses (H) that populations of M. pennsylvanicus would (H₁) increase in abundance and potentially fluctuate owing to the availability of early seral post-harvest habitats associated with cumulative clearcut harvesting; and (H₂) be positively associated with mean cover of herbaceous vegetation on clearcut sites; and (H₃) be at lower abundance when the long-tailed vole (M. longicaudus) is present at higher numbers. Overall, mean abundances of M. pennsylvanicus were generally low, and hence differences among Periods were not formally significant. Thus, H₁, that meadow voles would increase in abundance on new clearcuts was not supported, except for Period 2 with the highest mean density recorded at 14.3 voles/ha. There was some evidence of a 4-year multi-annual fluctuation in 1998 and 2002 in Period 2. Mean ground cover of total herbs, grasses, and shrubs were similar in Periods 2 and 3. However, meadow vole populations were dramatically different in these two Periods, with few meadow voles captured in Period 3 and then a decline to extirpation in Period 4. Thus, H₂ was supported for Period 2, but not Period 3. Both species of voles were present at similarly low numbers (< 5/ha) with fewer meadow voles in the three years of peak numbers (22–33/ha) of long-tailed voles, and hence this pattern provided weak support for H₃. The lack of increases in meadow vole numbers post-cutting in Periods 1, 3, and 4 may have been related to very high numbers of M. longicaudus in Period 1 and possibly the advent of cattle grazing and drought conditions in Periods 3 and 4. Although the decline in Microtus on post-harvest forest sites may be beneficial for pest management and reforestation, such declines may have serious consequences for predator communities, biodiversity, and other ecological functions.