Residual tree retention ameliorates short-term effects of clear-cutting onsome boreal songbirds

Retention of residual trees in "cutblocks," logged blocks of forest, has be en proposed as a method to conserve songbirds in landscapes fragmented by c lear-cut logging. We examined songbird communities in the boreal mixed-wood forest of Alberta, Canada, to investigate the effect on songbird abundance of (1) logging and (2) retaining variable densities of residual trees in c utblocks (10-133 trees/ha or basal area of 0.50-10.65 m(2)). We surveyed so ngbirds in logged and forested, aspen-dominated, mixed-wood stands in the y ear before, the year after, and three years after logging. We analyzed chan ges in abundance of 27 common songbird species: 23 present in the forest pr ior to logging and four that appeared after logging. Ten species declined w ith logging and were termed "forest species." Ten more species did not chan ge with logging and were called "habitat generalists." The seven species th at increased with logging were called "cutblock species." When the effect o f residual tree retention was examined in terms of basal area (rather than density) of residual trees, more songbird species were found to be both pos itively and negatively affected by residual tree retention, despite the fac t that the two tree measures were highly correlated. In the first year afte r logging, four bird species (two forest, one generalist, and one cutblock) increased, and none decreased with increasing residual tree retention in c utblocks. In the third year after logging, again four species increased wit h increasing retention, but these were different species than in the first year after logging (one forest and three generalist species). Furthermore, four cutblock species decreased with increasing retention. Based on these f indings, we conclude that retention of residual trees may be beneficial to some species, although conservation of unlogged reserves is also important. Most importantly, we recommend that research be continued to examine a lar ger range of tree retention and longer term effects on the avifauna.