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The role of the northern pocket gopher (Thomomys talpoides) in primary successional landscapes at Mount St. Helens
The northern pocket gopher (Thomomys talpoides) has been shown to strongly influence ecosystem dynamics in western North America through mound building and herbivory, resulting in altered plant communities and biogeochemical processes. Pocket gophers colonized the Pumice Plain of Mount St. Helens in 1992, 12 years after the 1980 eruption, and have expanded their population since that time. The objectives of the research are to determine the effects of pocket gophers on soil nutrient fluxes and pools as well as on plant community diversity in a primary successional system. I compared plant species percent cover and abundance on mounds, near mounds and in undisturbed areas. I also created artificial gopher mounds and compared rates of soil CO2, NO3-N, NH4-N, and PO4-P flux, and pools of soil nitrogen and carbon between artificial mounds and undisturbed areas. One year old artificial gopher mounds exhibited decreased rates of soil CO2 flux compared to undisturbed areas, while recently-created mounds (2 weeks old) showed no difference in soil CO2 flux rates. Additionally, there was no difference in NO3-N, NH4-N, and PO4-P flux rates. However, gopher mounds were characterized by increased soil total carbon and nitrogen compared to undisturbed areas. Young (1 year old) gopher mounds exhibited decreased species density and richness compared to near-mound, and undisturbed areas, while older (2 year old) mounds were not significantly different from near-mound and undisturbed areas. These results suggest that the relationship between gopher disturbance and soil nutrient fluxes are likely mediated by interactions between biotic and abiotic factors. Altered plant assemblages, soil microbial activity and soil hydrology result in soil nutrient pools and fluxes that are relatively resilient to physical disturbance