Influence of woody plant on spring and riparian vegetation in central Texas




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With the increase in human population, water resources have become more and more precious. A comprehensive study of water yield characteristics is imperative, especially in water-limited semiarid regions. The objective of this study is to examine spring flow and vegetation cover in a first-order watershed and investigate the herbaceous community structure of upland riparian zones. This study consists of two major components: (1) the effects of environmental factors and vegetation cover on spring flow at Pedernales River upland catchments, and (2) the ecological responses of vegetation to altered flow regimes that result from brush management at the upland riparian zones. The study finds that an average of 3.67% of the monthly water budget of first-order catchments in central Texas is made up of spring flow. The influence of woody plant cover on streamflow was evaluated by comparing spring sites with different percentages of woody cover three times during 2003 and 2004. Our findings indicate that changes in woody plant cover had no influence on the amounts of streamflow from these catchments, and the surface catchment area had only a minor influence. This suggests that the real spring catchment area might be different from the surface watershed boundaries that have been delineated by topography. Plant species richness and diversity gradually decreased with increasing lateral distances from the stream bank. Herbaceous richness and diversity declined with increasing Ashe juniper cover in the riparian zone. Ashe juniper canopy cover had a larger effect on the understory composition than the cover of other woody species. Herbaceous diversity and production was greater in areas with sparse tree density than in areas with no trees, but was lowest at high tree densities. The complete removal of Ashe juniper in the riparian zones is not recommended because of the potential loss of grass cover. The recommended management would be to leave a sparse cover of canopy trees to maintain understory plants.