Soil properties are resilient despite grass invasion, fire, and grazing

Abstract

Kentucky bluegrass (Poa pratensis L.; hereafter referred to as bluegrass) is an invasive perennial grass that has become naturalized throughout the entire United States. This species is an effective competitor and produces abundant litter, which in turn creates a thick thatch layer. In the northern Great Plains, fire and grazing are effective management tools for reducing the thatch layer, promoting expression of native grasses and forbs, and improving forage quality. The overall objective of this research was to examine belowground characteristics under accumulated thatch in response to management with fire and grazing. Soil samples were collected from plots dominated by bluegrass with thatch and from plots one year after management with fire and season-long grazing. Additionally, to understand immediate and in-season effects of fire and grazing on soil properties, we sampled soil immediately before and at increasing time steps after spring fires and exposure to grazing. All soils were analyzed for carbon and nitrogen pools, microbial abundance and community structure, and decomposition rates. In general, belowground pools of carbon, nitrogen, and microbial communities were stable despite vegetation management treatments. However, prescribed burning caused a brief decline of labile carbon and decomposition rates in shallow soil, but both properties returned to prefire levels within one year after burning. Our observations indicate that the combination of fire and grazing has minimal effect on the soil and is effective at removing thatch and reducing bluegrass.