Effects of mechanical strip thinning of aspen on small mammals and breeding birds in northern Minnesota, U.S.A.

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 were observed on sapling-sized thinned than reference stands, reflecting primarily decreases in abundances of bird species that select midsuccessional deciduous forests; several of these species are long-distance migrants. Bird abundance and community composition on thinned and reference pole-sized stands were similar, differing most notably in the presence of Canada Warbler (Wilsonia canadensis (L.)) and Downy Woodpecker (Picoides pubescens (L.)) in thinned but not reference stands. Significantly more individual small mammals were captured on thinned than reference stands, and most other measures of abundance indicated positive numerical responses of small mammals to strip thinning. Mechanical strip thinning of aspen shows promise for enhancing aspen supply by allowing trees to grow more rapidly to harvestable size. Our results suggest 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.