Relationships Between Bird Communities and Forest Age, Structure, Species Composition and Fragmentation in the West Gulf Coastal Plain

-Bird communities of the West Gulf Coastal Plain are strongly influenced by the stage of forest succession, species composition of understory and overstory vegetation, and forest structure. Alteration of plant communities through forest management and natural disturbances typically does not eliminate birds as a fauna1 group from the area affected, but will replace some species with others and cause changes in the abundance and species composition of bird communities. Upland, tire disclimax pine Savannah communities composed of primarily longleaf pine (Pinuspalustris) provide mature pines for Red-cockaded Woodpeckers (Picoides borealis) and Brown-headed Nuthatches (Sitta pusilla) while simultaneously providing grassland ‘ground cover for Bachman’s Sparrows (Airnophila aestivalis) and Henslow’s Sparrows (Ammodramus henslowii). On the mesic mid-slopes where there is an increasing presence of loblolly (P’tnus taeda) and shortleaf (Pinus echinata) pine and hardwood species, Northern Cardinals (Cardinalis cardinalis) and White-eyed Vireos (Vireo griseus) find habitat in the understory and midstory vegetation, whereas canopy hardwoods and pines provide habitat for Red-eyed Vireos (Vireo olivaceus) and Summer Tanagers (Piranga rubra). Transition into the wet bottomland hardwood forests increases the abundance of bird species associated with deciduous wetlands such as Prothonotary Warblers (Protonotaria citrea) and Swainson’s Warblers (Limnothlypis swainsonii), whereas species associated with conifers and grassland savannahs are lost. Anthropogenic or natural disturbances that set back mature stages of forest succession can dramatically alter the species composition of bird communities. Depending on patch size, forest removal can initiate forest succession and provide habitat for early succession bird species such as Blue Grosbeaks (Guiraca caerulea), Field Sparrows (Spizella pusilla), Prairie Warblers (Dendroica discolor), Painted Buntings (Passerina ciris), Indigo Buntings (Passerina cyanea), and Yellow-breasted Chats (Icteria virens). Although current data are inconclusive, patch size, forest fragmentation, edge effect, and landscape use patterns appear to influence bird communities by affecting area-sensitive species. Of greatest concern are forest-interior bird species that appear to be area sensitive such as the Cerulean Warbler (Dendroica cerulea), Northern Panda (Parula americana), Louisiana Waterthrush (Seiurus motacilla), American Redstart (Setophaga ruticilla), and Worm-eating Warbler (Helmitheros vermivorus). Forest bird communities of the West Gulf Coastal Plain are influenced primarily by forest age and structure, and tree species composition. Across the forest landscape, anthropogenic effects, that determine the spatial mosaic of forest age-classes and size of forest patches, also influence avian species composition and abundance. Seasonally, bird communities in the West Gulf Coastal Plain are affected by spring influx 124 THETEXASJOURNALOFSCIENCE-VOL,49(3)SUPPLEMENT, 1997 and departure of nearctic and neotropical migrants as they arrive from southerly latitudes to establish breeding territories, or stop briefly to feed and then quickly depart for more northerly breeding grounds. Until the mid 18OOs, the landscape of eastern Texas was primarily forest habitat with longleaf pine ecosystems dominating the frequently burned upland sites, bottomland hardwood forests in the lower mesic to wet sites, and loblolly and shortleaf mixed-pine hardwood forests spanning a dynamic zone between the sites of moisture extremes (Maxwell & Baker 1983; Walker 1991). During the late 1800s the rate of timber harvesting in the West Gulf Coastal Plain increased dramatically. A “bonanza era” of timber harvesting occurred from 1880 to 1930 which eliminated the majority of old-growth forests in eastern Texas (Maxwell & Baker 1983; McWilliams & Lord 1988). Upland pine forests and bottomland hardwood forests were both heavily logged. Some of the cut-overforest lands were reforested by artificial planting, some by natural seeding, while other lands were converted to agricultural uses and reservoirs (Truett & Lay 1984; Walker 1991). Thus, the present-day forests that provide habitat for bird communities are secondgrowth forests, which have again been affected by harvesting during the past several decades (McWilliams & Lord 1988). This paper presents an abbreviated glimpse of general relationships between birds and their habitats using selected species as illustrations. Our objective is to demonstrate that avian communities are variable, but are also dependent on forest stand age, tree species composition, season, special habitat features such as snags, and the mosaic of age classes across the forest landscape that affect forest fragmentation. Relationships between selected sensitive species, loss of old-growth habitat, and forest fragmentation will also be examined. THE INFLUENCE OF FOREST STAND A GE ON AVIAN CO M M U N I T I E S Timber harvesting, and largeand small-scale natural disturbances greatly affect the species composition of bird communities. Typically in the South, species are not eliminated from the forest landscape, but are temporally replaced by others as timber stand age is affected by forest management and natural forest succession (Odum 1950; Conner & Adkisson 1975; Conner et al. 1979; Dickson et al. 1993a; 1993b). Early succession seres created by disturbances such as wind throw, bark beetle infestation, or timber harvesting provide breeding habitat for field CONNER & DICKSON 125 EARLY SUCCESSION SPECIES