Vegetation responses to different spatial patterns of soil disturbance in burned and unburned tallgrass prairie
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Pocket gopher (Geomyidae) disturbances are created in spatially predictable patterns. This may influence resource heterogeneity and affect grassland vegetation in a unique manner. We attempt to determine the extent to which density and spatial pattern of soil disturbances influence tallgrass prairie plant community structure and determine how these disturbances interact with fire. To investigate the effects of explicit disturbance patterns we created simulated pocket gopher burrows and mounds in various spatial patterns. Simulated burrows were drilled into the soil at different densities in replicated plots of burned and unburned prairie. Separate plots of simulated mounds were created in burned and unburned prairie at low, medium, or high mound densities in clumped, uniform, or random spatial dispersions. In both burned and unburned plots, increased burrow density decreased graminoid biomass and increased forb biomass. Total-plant and graminoid biomass were higher in burned than unburned plots while forb biomass was higher in unburned plots. Total-plant species richness was not significantly affected by burrow density or burning treatments, but graminoid species richness increased in unburned plots and forb species richness increased in burned plots. Plant species richness was temporarily reduced directly on mound disturbances compared to undisturbed prairie. Over time and at larger sampling scales, the interaction of fire and mound disturbance patterns significantly affected total-plant and graminoid species richness. The principal effect in burned and unburned prairie was decreased total-plant and graminoid species richness with increased mound disturbance intensity. Although species richness at small patch scales was not increased by any intensity of disturbance and species composition was not altered by the establishment of a unique guild of disturbance colonizing plants, our study revealed that interactions between soil disturbances and fire alter the plant community dominance structure of North American tallgrass prairie primarily via changes to graminoids. Moreover, these effects become increasingly pronounced over time and at larger spatial sampling scales.