Estimating burrow volume and excavation rate of pocket gophers (Geomyidae)
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Burrowing animals fundamentally influence the character of soils, ecosystem function, erosion, and soil management for food production and hazardous wastes. Perhaps the most important indicator of their potential impacts is the average void space created for burrow construction and maintenance per unit area per unit time. We integrated published estimates of burrow volume (m3) and excavation rates (m3 ha-1 year-1) of pocket gophers (Rodentia: Geomyidae) to assess their reliability in assessment of impacts and whether these variables are scale-dependent. Estimates were difficult to interpret and compare because research goals, assumptions, and methods varied considerably among studies, as did site conditions and reporting of results. Volume of burrows made by various species of pocket gophers averaged 0.68 m3, and averages differed significantly between species. Rate of excavation averaged 18 m3 ha-1 year-1 for Geomyidae, and it declined with increasing spatial extent of study area used to make the estimates. Counts of mounds produced the largest estimates of burrow volume and excavation rate, and injection of polyurethane foam into burrows produced low estimates. High variation in estimated rates of burrow excavation indicates the need for further research to characterize magnitude and types of impacts gophers have on natural and managed ecosystems.
