Clearcutting and burning of northern spruce-fir forests: implications for small mammal communities.
Abstract
A study was conducted to test the hypotheses that (i) abundance and related demographic parameters of small mammal populations would decline after clear-cutting of northern spruce-fir forest, and (ii) prescribed burning, following clear-cutting (an approach to emulating natural disturbance), would enhance the species richness and diversity of the small mammal community relative to unharvested and clearcut forests. Intensive live-trapping of small mammal populations was conducted in replicated forest (uncut), clearcut and clearcut-burned sites from 1988-92 in west-central British Columbia, Canada. The dominant species at these 3 sites were Abies lasiocarpa, Pinus contorta and Picea engelmannii × Picea glauca. Mean abundance of Clethrionomys gapperi was significantly higher on forest sites (11.74 ha-1) than on clearcut (0.60 ha-1) or clearcut-burned (0.02 ha-1) sites. Mean numbers of Peromyscus maniculatus were significantly higher on the clearcut-burned sites (16.88 ha-1) than on forest sites (9.04 ha-1). Demographic parameters of reproduction, survival and body weight of P. maniculatus were similar across all sites. Microtus longicaudus had a strong annual fluctuation in abundance, particularly on clearcut sites (14.04 ha-1), where there were significantly more animals than on either forest (1.53 ha-1) or clearcut-burned (2.67 ha-1) sites. M. pennsylvanicus were relatively uncommon but occurred more often on clearcut and clearcut-burned sites than on forest sites. The north-western chipmunk Tamias amoenus occurred at significantly higher numbers on clearcut (4.16 ha-1) and clearcut-burned (3.88 ha-1) sites than on forest sites, where it was rarely captured. Sorex spp. were at similar numbers across forest, clearcut and clearcut-burned sites. Weasels (Mustela spp.) were captured more often on clearcut and clearcut-burned sites than on forest sites. A rare species, the western jumping mouse Zapus princeps, was captured on clearcut and clearcut-burned sites only. Mean species richness of small mammals was significantly higher on clearcut sites (3.51) than on forest (2.73) or clearcut-burned (2.72) sites. Species diversity was similar over all sites. Although species composition was altered by clearcutting, abundance of all species, except C. gapperi, was the same or higher than that in uncut forest. It is suggested that prescribed burning of clearcuts may not be necessary to mimic natural disturbance regimes, and that clearcutting of northern spruce-fir forest may provide diverse habitats for small mammals through different stages of succession (along with old growth forest) much as wildfires formerly did.