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Susan Schwinning's Current Research Projects

 

Woody encroachment at the seedling stage

  NSF Logo

Woody encroachment is the global phenomenon of shrub and tree proliferation in grasslands and savannas. Fire suppression and livestock grazing are widely held responsible for this vegetation change, but these factors do not explain why some woody species encroach and others do not. This project examins the critical establishment phase to determine which seedling traits are associated with high rates of establishment and rapid seedling growth under conditions of variable rainfall and competition from grasses. This project is supported by the National Science Foundation.

     

Ecohydrology of the Texas Hill Country, a karst savanna

  Karst

Karst is a landform that establishes over highly soluable rocks such as limesone. The high erodability of the rock produces fissures, sinkholes, underground streams, and caverns, which render the subsurface hydrological conditions spatially complex and highly dynamic, frequently alternating between extreme water scarcity and flash flooding. How plant roots navigate this unusual substrate and utilize its water stores is largely unknown. This project aims to characterize patterns of root growth and water uptake by overstory trees, understory shrubs and grasses, using stable isotope and other ecophysiological techniques. This project is supported by Texas State University's Research Enhancement Program.

     

Mechanisms of plant coexistence through water partitioning

  Functional Division

The hypothesis that plants in water-limited regions coexist by virtue of partitioning water in space and time is not new. However, this hypothesis has not been fully integrated with modern competition theory, which describes general mechanisms of coexistence among competitors based on competition-environment interactions iwith stochastic drivers. This modeling project examines the potential of well-known morphological and physiological adaptations of desert plants, such as in root distribution, water use efficiency and phenology, to faciltate coexistence in water-limited environments.

     

Ecological effects of roads in the Mojave Desert

  Mojave Desert

Desert washes on alluvial soils naturally organize into fractal channel networks. The largest channels exclude vegetation because of the severe disturbances experienced by plants during flash floods. However, plants at the margins of large washes are often bigger, taking advantage of the occasional water subsidies from upland areas. Large washes eventually fan out into smaller channels which redistribute water more evenly across the land. These natural channel networks are disrupted by road building, as culverts redirect water into extremely large channels. This project examins how this disuption of natural runoff flows changes spatial and temporal vegetation patterns and associated ecological processes such as soil geochemistry and plant-animal interactions. This project is a collaboration with the US Geologic Survey.