Vegetation composition and organic carbon content along right-of-ways on interstate highway 35 in Bexar County, Texas

Abstract

Roadside habitat through major urban areas may offer remnant examples of natural grasslands. These habitats may be subjected to frequent as mowing and exposure to automobile emissions and runoff. This study was conducted on interstate highway right-of-ways in San Antonio, Texas, U.S.A. We compared the vegetation species and diversity, and the organic carbon of leaf litter, plants, and soils. Two non-native grasses accounted for 50.9 % cover, while all native forbs and grasses accounted for only 9.8 % cover. The mean biomass of non-native grasses was 4.5 times greater than that of all native species. Organic carbon content of leaf litter, plants, and soils was variable among the study sites, possibly due to management practices and a drought that occurred during the study. The mean organic carbon content in the upper 20 cm soil was 5.0 kg C/m² and organic carbon content was greater in the upper 10 cm than organic carbon in the 10.1 to 20 cm portion. Cynodon dactylon and Bouteloua curtipendula exhibited the greatest photosynthesis efficiency indicating these grasses are more adaptable to hot summer temperatures found in Central Texas. The organic carbon content along a major interstate was 13,793 kg·C/ha for leaf litter, vegetation, and the upper 20 cm of the soil. We conclude that interstate highways provide habitat for some native species, but the vegetation along right-of-ways is dominated by two non-native grasses. It appears unlikely that roadside habitat can be restored to resemble native grasslands without large scale and costly restoration efforts.