EFFECTS OF MECHANICAL STRIP THINNING OF ASPEN ON SMALL MAMMALS AND BREEDING BIRDS IN NORTHERN MINNESOTA, USA

Abundance and species composition of small mammals and breeding birds were studied on mechanically strip-thinned aspen stands and comparable reference stands in northern Minnesota, Strip-thinned stands included sapling-sized stands thinned 1 or 2. years before the study and pole- sized stands thinned 7-11 years previously. Fewer individual birds wer e observed on sapling-sized thinned than reference stands, reflecting primarily decreases abundances of bird species that select midsuccessi onal deciduous forests; several of these species are long-distance mig rants. Bird abundance and community composition on thinned and referen ce pole-sized stands were similar, differing most notably in the prese nce of Canada Warbler (Wilsonia canadensis (L.)) and Downy Woodpecker (Picoides pubescens (L.)) in thinned but not reference stands. Signifi cantly more individual small mammals were captured on thinned than ref erence stands, and most other measures of abundance indicated positive numerical responses of small mammals to strip thinning. Mechanical st rip thinning of aspen shows promise for enhancing aspen supply by allo wing trees to grow more rapidly to harvestable size. Our results sugge st that use of this practice has no negative effects on small mammals and relatively short-lived negative effects on forest songbirds at the stand level.