Breeding bird assemblages of hurricane-created gaps and adjacent closed canopy forest in the southern Appalachians

We studied breeding bird assemblages in forest gaps created in 1995 by Hurr icane Opal at the Bent Creek Experimental Forest in Asheville, NC. We hypot hesized that forest gaps and adjacent closed-canopy forest would differ in bird density, richness, diversity, and relative abundances of some species. To test this hypothesis we censused breeding bird assemblages for 2 years in 12 gaps (0.1-1.2 ha) and 12 adjacent closed canopy controls using strip transects. Gaps had more coarse woody debris, shrub cover, brushpiles, and pit and mound microtopography than controls. Canopy cover was lower in gaps than controls, but remained high (69.4 +/- 2.1% versus 89.6 +/- 1.7%). Bir d assemblage similarity was high. Total density and species richness of bir ds were higher in gaps than in controls, but species diversity did not diff er between treatments. Shrub (primarily Carolina Wrens) and bark-foragers, and cavity shrub and canopy-nesters were more abundant in gaps than in cont rols. Densities of gap-associated (Indigo Bunting, Hooded Warbler, Carolina Wren) and edge (Eastern Towhee) species were more abundant in gaps. Abunda nce of interior species including Red-eyed Vireo and Scarlet Tanager were a bout equal in gaps and controls. Only Ovenbirds were more abundant in contr ols than gaps. Species that require larger patches of young second-growth f orest, such as Prairie Warbler, and Yellow-breasted Chat, did not occur in gaps: but neither are they abundant in the Asheville basin. No Brown-beaded Cowbirds were observed in gaps or controls. Unpublished data indicate that parasitism of artificial ground nests did not occur, and predation rates d id not differ between gaps and controls. Juvenile birds and other evidence of breeding were observed more often in gaps than in controls, suggesting t hat gaps attract bird families for foraging and provide microsites that att ract breeding pairs. Gap size was positively correlated with bird density, species richness, and diversity. This study suggests that small openings an d interior edge habitat created by treefall gaps within a forested matrix d o not adversely affect breeding birds as measured by the abundance of indiv idual species or community indices. We suggest that canopy gaps increase av ian diversity at a landscape scale by providing habitat patches for some sp ecies that require young, second-growth forest, and serve as magnets for re cruitment and foraging. (C) 2001 Elsevier Science B.V. All rights reserved.