We studied breeding bird assemblages in forest gaps created in 1995 by Hurricane Opal at the Bent Creek Experimental Forest in Asheville, NC. We hypothesized 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 AE 2:1% versus 89:6 AE 1:7%). Bird assemblage similarity was high. Total density and species richness of birds were higher in gaps than in controls, but species diversity did not differ between treatments. Shrub (primarily Carolina Wrens) and bark-foragers, and cavity shrub and canopy-nesters were more abundant in gaps than in controls. Densities of gap-associated (Indigo Bunting, Hooded Warbler, Carolina Wren) and edge (Eastern Towhee) species were more abundant in gaps. Abundance of interior species including Red-eyed Vireo and Scarlet Tanager were about equal in gaps and controls. Only Ovenbirds were more abundant in controls than gaps. Species that require larger patches of young second-growth forest, such as Prairie Warbler, and Yellow-breasted Chat, did not occur in gaps; but neither are they abundant in the Asheville basin. No Brown-headed Cowbirds were observed in gaps or controls. Unpublished data indicate that parasitism of arti®cial ground nests did not occur, and predation rates did not differ between gaps and controls. Juvenile birds and other evidence of breeding were observed more often in gaps than in controls, suggesting that gaps attract bird families for foraging and provide microsites that attract breeding pairs. Gap size was positively correlated with bird density, species richness, and diversity. This study suggests that small openings and interior edge habitat created by treefall gaps within a forested matrix do not adversely affect breeding birds as measured by the abundance of individual species or community indices. We suggest that canopy gaps increase avian diversity at a landscape scale by providing habitat patches for some species that require young, second-growth forest, and serve as magnets for recruitment and foraging.
Large home-range size and habitat specificity are two commonly cited ecological attributes that are believed to contribute to species vulnerability. The eastern diamondback rattlesnake Crotalus adamanteus is a declining species that occurs sympatrically with the more abundant canebrake rattlesnake Crotalus horridus in a portion of the south-eastern Coastal Plain, USA. In this study, we use the ecological similarities of the two species as experimental controls to test the role of home-range size and habitat specificity in the imperilment of the eastern diamondback rattlesnake. We used analysis of variance to investigate differences in home-range size between the two species, and home-range selection was modeled as habitat use versus availability with a case control sampling design using logistic regression. We failed to detect differences in home-range size between the two species; therefore, we could not identify home-range size as an attribute contributing to the imperilment of eastern diamondback rattlesnakes. Eastern diamondback rattlesnakes selected pine savannas to a degree that suggests that the species is a habitat specialist. Of the two factors examined, habitat specificity to the imperiled longleaf pine ecosystem may be a significant contributor to the decline of the eastern diamondback rattlesnake.
We compared the effects of 3 fuel reduction techniques and a control on breeding birds during 2001‐2005 using 50‐m point counts. Four experimental units, each >14 ha, were contained within each of 3 replicate blocks at the Green River Game Land, Polk County, North Carolina, USA. Treatments were 1) prescribed burn, 2) mechanical understory reduction (chainsaw‐felling of shrubs and small trees), 3) mechanical + burn, and 4) controls. We conducted mechanical treatments in winter 2001‐2002 and prescribed burns in spring 2003. Tall shrub cover was substantially reduced in all treatments compared to controls. Tree mortality and canopy openness was highest in the mechanical + burn treatment after burning, likely due to higher fuel loading and hotter burns; tree mortality increased with time. Many bird species did not detectably decrease or increase in response to treatments. Species richness, total bird density, and some species, including indigo buntings (Passerina cyanea) and eastern bluebirds (Sialia sialis), increased in the mechanical + burn treatment after a 1‐year to 2‐year delay; eastern woodpewees (Contopus virens) increased immediately after treatment. Hooded warblers (Wilsonia citrina), black‐and‐white warblers (Mniotilta varia), and worm‐eating warblers (Helmitheros vermivorus) declined temporarily in some or all treatments, likely in response to understory and (or) leaf litter depth reductions. Densities of most species affected by treatments varied with shrub cover, tree or snag density, or leaf litter depth. High snag availability, open conditions, and a higher density of flying insects in the mechanical + burn treatment likely contributed to increased bird density and species richness. In our study, fuel reduction treatments that left the canopy intact, such as low‐intensity prescribed fire or mechanical understory removal, had few detectable effects on breeding birds compared to the mechanical + burn treatment. High‐intensity burning with heavy tree‐kill, as occurred in our mechanical + burn treatment, can be used as a management tool to increase densities of birds associated with open habitat while retaining many forest and generalist species, but may have short‐term adverse effects on some species that are associated with the ground‐ or shrub‐strata for nesting and foraging.
Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guided disturbance ecology for decades, generating mixed scientific evidence of biodiversity responses to disturbance. Understanding the impact of natural disturbances on biodiversity is increasingly important due to human-induced changes in natural disturbance regimes. In many areas, major natural forest disturbances, such as wildfires, windstorms, and insect outbreaks, are becoming more frequent, intense, severe, and widespread due to climate change and land-use change. Conversely, the suppression of natural disturbances threatens disturbance-dependent biota. Using a meta-analytic approach, we analysed a global data set (with most sampling concentrated in temperate and boreal secondary forests) of species assemblages of 26 taxonomic groups, including plants, animals, and fungi collected from forests affected by wildfires, windstorms, and insect outbreaks. The overall effect of natural disturbances on α-diversity did not differ significantly from zero, but some taxonomic groups responded positively to disturbance, while others tended to respond negatively.
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