BIRD COMMUNITIES AFTER BLOWDOWN IN A LATE-SUCCESSIONAL GREAT LAKES SPRUCE-FIR FOREST

Abstract

In 2001 and 2002, we inventoried the bird communities and vegetation of two 6.25-ha plots in a late-successional spruce-fir (Picea mariana–Abies balsamea) forest of northern Minnesota that was severely disturbed by a 1999 windstorm. We compared these results with those from two nearby plots that were largely unaffected by the storm. Using vegetation data collected from one of the two plots in each location before the disturbance in 1996 and 1998, we examined similarities between plots before and after the storm. The most significant effect of the storm on vegetation was a ≥80% decrease in tree cover and a >100% increase in shrub-layer structure because of trees that were tipped over or snapped off. Of 30 territorial bird species, 9 held territories exclusively in the blowdown, while 2 held territories exclusively in the control. By foraging guild, 10 of 11 (91%) species of ground-brush foragers had more territory cover in the blowdown, while 7 of 13 (54%) species of tree-foliage searchers had more territory cover in the control. Black-and-white Warbler (Mniotilta varia), Chestnut-sided Warbler (Dendroica pensylvanica), Mourning Warbler (Oporornis philadelphia), Yellow-bellied Flycatcher (Empidonax flaviventris), and Red-eyed Vireo (Vireo olivaceus) had significantly (P < 0.05) more territory cover in the blowdown, whereas Blackburnian Warbler (Dendroica fusca), Golden-crowned Kinglet (Regulus satrapa), and Yellow-rumped Warbler (Dendroica coronata) had more territory cover in the control. Canonical correspondence analysis revealed that differences in avian territory cover were primarily attributable to changes in vegetation structure, in particular the increase of structural debris on the ground and the reduction in tree canopy, occurring because of the wind.