Graduate Thesis Or Dissertation
 

Assessing cumulative influences of watershed-scale landuses on reed canarygrass (Phalaris arundinacea L.) abundance

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h702q924b

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  • The West Eugene Wetlands, Eugene, Oregon, which provide habitat for number of endemic and endangered plant species, are currently threatened by a Reed canarygrass (Phalaris arundinacea L.) invasion. This study addresses the hypothesis that Phalaris spread can be explained in part by using watershed-scale landuse patterns as surrogates of the water quality and hydrologic regime in the associated watersheds. A multiple regression model was constructed to test the effects of watershed-scale landuses on Phalaris abundance. The spatially referenced landuse attributes were estimated using accumulated inverse-squared flow path distances between each wetland and cells in a grid-based representation of landuse/cover data in a Geographic Information System. The locally measured physical and biological characteristics of wetlands were also incorporated into the model to adjust for site differences. Bias in the estimated parametric coefficients were found to be negligible using 1,000 iterations of a bootstrap re-sampling technique. Bias-corrected-and-accelerated intervals also supported the significance of these estimates. The inferential model, consisting of the percentage open water cover in the wetlands, an indicator of highly disturbed site and watershed-scale urban and forest landuses, explained 67 percent variation of Phalaris abundance. There was convincing evidence that the cumulative watershed-scale landuse patterns affected Phalaris abundance (p-value < 0.001; extra-sum-of-squares F-test). In particular, urbanization was strongly associated with greater Phalaris abundance (p-value = 0.00001, two-sided t-test). The effects of watershed-scale landuse appeared to be persistent in the inside of the wetland edges. Implications for wetland management were discussed. Alternative restoration strategy addressing plant diversity was also proposed.
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