Assessing biological values of Wetland Reserve Program wetlands for wintering waterfowl Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/t435gg283

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  • The Wetland Reserve Program (WRP) is one conservation tool that mitigates national wetland loss and a primary goal for the program includes optimizing wildlife habitat by restoring wetland functions and values. Few studies have evaluated the WRP, which limits our understanding of its impact on wildlife populations. I assessed the biological value of seasonal wetlands on WRP easements in the Willamette Valley (WV) and Lower Columbia River Valley (LCRV) of western Oregon and southwest Washington by comparing plant communities and waterfowl food production (i.e. seed biomass) to publicly managed wetlands that served as reference conditions. Estimating waterfowl food resources is used to evaluate habitat quality, restoration, management, and developing habitat specific conservation plans for wintering waterfowl. The most common technique to estimate the portion of seed in wetland soils is to collect and process soil cores, yet there is variability in the depth of cores collected because it is unknown how deep dabbling ducks can extract food from the substrate. Furthermore, recent food abundance studies have not partitioned food estimates by location within wetlands (i.e. above or below ground), which has implications for understanding food availability for ducks. I sampled 23 wetlands for each wetland type in fall 2008 and 2009. I determined the proportion of seeds above versus below ground and the vertical distribution of seed biomass within the soil profile by partitioning samples in 26 wetlands in 2008. There was significantly more seed biomass above ground (72%, 362 ± 50.8 kg/ha) than below (28%, 141 ± 18.5 kg/ha). Seed biomass also varied by soil depth layer with greater biomass in 0-2 cm than both 2-5 and 5-10 cm layers. The majority of seed biomass within the soil was in was in the top 5 cm of the soil profile (75%). I detected 113 plant genera/species and the total mean percent cover of all plant species was 49% native, 38% introduced, 13% bare ground, and 3% unknown. Plant communities differed between study regions but not by wetland type. Twenty-nine species differed by region with more annuals being indicative of the WV and perennial species in the LCRV. Overall, the mean seed biomass estimate was 505 ± 59 kg/ha. Seed biomass was similar between wetland type and study region; however, WRP wetlands in the WV produced more seed (560 ± 114 kg/ha) than those in the LCRV (188 ± 43 kg/ha). Lower seed production in the LCRV WRP sites was attributed to a dominance of perennial species, predominantly Phalaris arundinacea that produced low seed yields relative to annual plants. My results indicate most seed was near the soil surface with only 36 kg/ha in the 5-10 cm layer, providing evidence that most seed is available to foraging dabbling ducks. Reference sites and WV WRP seasonal wetlands produced seed biomass that was similar to managed wetlands in other major waterfowl wintering areas in the United States. Therefore, WRP is capable of mitigating wetland loss and contributing to the regional goals of the North American Waterfowl Management Plan. However, WRP and reference seasonal wetlands are only providing 10% and 3.5% of dabbling ducks energetic demands in the WV and LCRV respectively due to a lack of habitat. Depending on whether the current landscape is meeting current dabbling duck energetic demands, this suggests either a need for more habitat, which is most feasible through restoration on private lands, or protecting other existing wetland habitats.
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