Gopher disturbance and plant community dynamics in montane meadows

Pocket gophers (Geomyidae) are a major agent of disturbance in grassland plant communities throughout North America. By depositing excavated soil on the ground surface, they bury existing plants and restart succession on a local scale, potentially influencing community structure and diversity by providing opportunities for less competitive species to persist. This study examined the impact of the Mazama pocket gopher (Thomomys mazama) on montane meadow plant communities in four plots established at Bunchgrass Ridge in the Oregon Cascade Range. Each plot contained 20
transects that were sampled for percent cover of gopher disturbance and plant species present. In higher-altitude systems such as Bunchgrass Ridge, gopher disturbance occurs as mounds, which are piles of excavated soil, as well as tunnel castings, which are created when gophers tunnel through a deep snow pack and fill these tunnels with soil that settles
on the ground surface after snow melt. The relationship between castings and vegetation has not previously been studied. I found that both mounds and castings negatively affected plant cover, and that species richness and spatial heterogeneity were positively correlated with total cover of isturbance. Cover of graminoids declined and the ratio of forb/graminoid cover increased with mound cover, which is consistent with the literature, but the relationship between graminoid cover and cover of castings appeared variable across the four plots sampled. As one explanation for these findings, I present a simulation model that demonstrates how the presence of a highly competitive species might alter the relationship between graminoids and disturbance. This study illustrates the critical role disturbance can play in structuring natural communities.