The Big Bend reach of the Rio Grande/Bravo (RGB) is a large, international dryland river system that is experiencing dramatic changes in river hydrology as a result of flow regulation and anthropogenic activities. This research evaluates the plant community composition and recent trends in riparian vegetation change along the Big Bend reach of the RGB by identifying dominant vegetation types growing along the shores and characterizing the variation in plant diversity and local environmental site conditions among these vegetation types. Vegetation observations were collected using a rapid landscape assessment and monitoring methodology along a 350 river-km reach in 2016 and then again in 2019. Based on the field data, I used a cluster analysis to identify four major vegetation types for the Big Bend reach of the RGB that differed significantly in plant species composition. I evaluated how local environmental characteristics influenced 1) plant community composition and 2) vegetation change over the sampling interval and I derived a suite of nine raster environmental variables to evaluate differences in hydrological cycling within different plant communities, including evapotranspiration (ET) and evaporative stress index (ESI) data from the ECOSTRESS satellite on the International Space Station. Despite local-scale changes in individual species composition along the RGB in both treated and untreated reaches, the plant community as a whole did not experience significant change in landscape-scale composition from 2016 to 2019. The vegetation types that displayed the highest evapotranspiration rates for both mean annual and summer ET were the ones that were high in species richness and biodiversity. This relationship may be due to the heterogeneity of species composition within the vegetation type and suggest that the nonnative species are not dominating and overwhelming their environments so that native taxa cannot coexist in the same habitat. Additionally, percent cover change analyses in treated reaches of the river revealed that native taxa could be experiencing some recovery following prescribed treatment for the monotype stands of nonnative giant cane (Arundo donax L.) that dominate many river valleys and lowlands of the RGB. Understanding how dryland riparian plant communities may shift in composition under future climatic and environmental conditions will be crucial for ecosystem managers and scientists who are interested in conserving and maintaining these critical biodiversity hotspots as most projections for riparian communities indicate that increasing climate change and anthropogenic disturbance of natural flow regimes will disproportionately impact dominant native riparian taxa. Studies like these provide an opportunity for characterizing riparian plant community dynamics and change over time that can help identify areas of nonnative species colonization and direct treatment management plans in order to preserve native biodiversity of these fragile riparian ecosystems.
"},{"label":"Degree","value":["Bachelor of Arts with Departmental Honors"]},{"label":"Administrative Note","value":"Drupal Node ID: 24111