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Publication Date

7-1-2004

Abstract

The adverse impacts of exotic vegetation on native flora and fauna are well documented in many ecosystems. However, there is little data on the effects of exotic vegetation on native wildlife in the South Texas Plains. The objective of this study was to determine if the abundance and diversity of breeding birds and native flora differed between areas dominated by native grasses and areas dominated by the exotic grasses Lehmann lovegrass (Eragrostis lehmanniana) and bufflegrass (Cenchrus ciliaris). Three native and 3 exotic grass dominated sites were selected for study on the Chaparral Wildlife Management Area and Piloncillo Ranch. Point counts were used to sample bird communities during spring 2001 and 2002. Line intercept, Daubenmire frame, and profile board methods were used to characterize shrub cover, herbaceous ground cover, and vertical structure, respectively. Native grass areas had higher forb and grass species richness and diversity. Percent forb canopy cover was greater on native grass sites. Important grasses including bristlegrasses (Setaria spp.) and fall witchgrass (Digitaria cognata) and beneficial forbs such as slender evolvulus (Evolvulus alsinoides), shaggy portulaca (Portulaca pilosa), and scarlet pea (Indigofera miniata) had greater cover on native grass areas. Bird density and diversity were greater in native grass rangelands. Lark Sparrow (Chondestes grammacus), Black-throated Sparrow (Amphispiza bilineata), Northern Mockingbird (Mimus polyglottos), and Northern Bobwhite (Colinus virginianus) consistently had higher densities in native grass areas. Bird species on our study sites appear to prefer native grass areas and may be exhibiting optimal foraging by selecting patches with a higher abundance and diversity of native vegetative resources. Additionally, exotic grasses may have a negative impact on the abundance and diversity of arthropods, which are a critical resource for birds during the breeding season. Future research should address this in addition to the impacts of exotic grass invasions on wintering birds and avian reproductive success.

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