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Q.2-06: Estimating the impact of delayed drawdown on seed production

Presented by Dan J. Smith - Email: djssmith@ucdavis.edu

In an attempt to mitigate the dramatic loss of wetland habitat in Californias Central Valley, wetland managers extensively manipulate remaining wetlands to provide foraging habitat for wintering waterfowl. Providing information to wetland managers so they can improve wetland productivity and thus waterfowl carrying capacity is essential for the future viability of wintering waterfowl in California. Drawdown date is an influential factor in determining germination success of wetland plants that provide food resources to wintering waterfowl. By delaying drawdown into spring, wetland habitat that is typically only available in winter becomes available for breeding waterfowl and numerous other wetland depend species. This study seeks to determine the impact of delayed drawdown on vegetation composition and height, biomass production, and seed production of waterfowl food plants. Three drawdown dates, the 15th of March, April and May, were tested. To examine the interaction between drawdown timing and irrigations, half of the replicates in each treatment group received a ten day summer irrigation six weeks after drawdown. These treatments were implemented in 18 research wetlands, each 1.58 acres in size. Vegetation composition was measured using percent cover, vegetation height was measured, and seed abundance was quantified using soil cores and vegetation clippings. We found that the Early drawdown treatment resulted in the tallest vegetation. Biomass production was not influenced by drawdown treatment, yet biomass produced in the first year was significantly greater than the second. While we found no effect of drawdown on total seed abundance, we did find species-specific responses. Both seed abundance and percent cover for Echinochloa crus-galli was greatest in the late irrigated treatment, while Crypsis schenoides plant and seed abundance was greatest in early irrigated treatment. These results indicate that wetlands can be managed to produce food for wintering waterfowl while also providing spring habitat for a multitude of species
Session: Poster Session 2 (Wednesday, August 28, 19:00 to 21:00)