Dissertation Research: Persistence mechanisms of pioneer riparian forests in meandering rivers

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The cottonwood (Populus) and willow (Salix) trees that line river corridors in semi-arid regions play key roles in nutrient cycling and soil development, provide shade that can reduce water temperatures, and are an important food source for terrestrial and aquatic organisms. These species, which typically establish on newly exposed substrate left after flood events, have experienced significant declines in North America due to land conversion and the regulation of river flows by dams. The habitat for establishment of these species that has been best understood, point bars in river bends, has been severely limited by river regulation, creating a need to better understand establishment processes in other locations. Abandoned channels, or oxbow lakes, are a common feature associated with many meandering rivers. Their importance as refugia for mobile aquatic organisms, such as fish, has long been recognized. Abandoned channels also may provide habitat suitable for the establishment and persistence of cottonwood and willow. A conceptual model that links sedimentation and vegetation dynamics within abandoned channels suggests that conditions change through time from a period during which physical factors dominate forest dynamics to conditions driven more by biotic interactions, particularly competition for light and water. This model will be tested with a community competition study along a realistic environmental gradient. This research, focused in the Central Valley of California, involves collaborators across disciplines and resource managers at government agencies and The Nature Conservancy. Input from managers was solicited early in study development, and researchers continue to actively engage with this community so that information can be exchanged early and often. Additional broader impacts will result from training a doctoral student and involving undergraduate students in the research.