Date of this Version
Prairie Naturalist (March 1984) 16(1): 5-10.
Our results indicate that mowing, like burning, greatly reduces the use of an area by Microtus and increases the density of Peromyscus maniculatus until the grass can grow back. Depending on the rate of growth of the grass this process can take more than a year. If the prairie is mowed every year to maximize the production of hay, populations of Microtus cannot be maintained at high densities.
The study site, Nine Mile Prairie, is one of the few natural tallgrass prairies remaining in eastern Nebraska. It covers about 240 acres and is located 5 km north and 9 km west of Lincoln, Nebraska. The area used in this study has never been plowed and for the last 75 years has been mowed. The vegetation of Nine Mile Prairie has been extensively studied by Steiger (1930).
Our finding that the density of Microtus is significantly related to cover is consistent with the patterns found by workers studying fire ecology (Schramm 1970), mowing effects (LoBue and Darnell 1959) and habitat structure (Birney et aI., 1976). Birney et al. (1976) discussed the need of heavy cover for high densities of Microtus. Our results produce a similar prediction and we conclude from both these studies that the above-ground cover of grass must reach around 700 g/m' to support populations of Microtus at high densities. How quickly this much vegetation accumulates on a tallgrass prairie is dependent on rainfall. However, at least one growing season would be necessary under ideal situations, and it might take several years with low rainfall. Perhaps of equal interest is the response of Microtus to the lower end of vegetative cover. We find that when vegetative cover is lower than 280 g/m2 there is a precipitous drop in vole density. Mowing reduces the cover below this level and therefore will make an area temporarily unsuitable for Microtus.