The effect of gopher mounds and fire on the spatial distribution and demography of a short-lived legume in tallgrass prairie

Abstract

Many studies have reported that gopher mounds can increase species diversity and spatial heterogeneity of plant communities, but few studies have experimentally linked these small-scale disturbances to spatial heterogeneity in the distribution of individual plant populations. In this study, we directly tested for a spatial relationship between the pattern of gopher mound production and the distribution of a short-lived legume, Medicago lupulina L., across a tallgrass prairie remnant. In addition, we conducted a 3-year study examining the demographic response of M. lupulina to mound and off-mound planting treatments, during which a spring fire occurred one year. We found that the spatial distribution of M. lupulina was positively correlated with the distribution of mounds. Germination was significantly greater off mounds in all years, while survivorship and fecundity were significantly greater on mounds in the 2 years without fire. During the fire year, survivorship was significantly greater off mounds and fecundity was approximately equal on and off mounds. We conclude that the positive spatial relationship between M. lupulina and mounds is caused by the direct dependence of M. lupulina on mounds for survivorship in most years. Gopher mounds provide microsites where plant competition and risk of herbivory are reduced. Overall, gopher mounds can directly produce spatial heterogeneity in the plant community, but the strength of this effect may be significantly modified in some years, particularly those in which a spring fire occurs.Key words: gopher mounds, fire, Medicago lupulina, disturbance, prairie, introduced species.