Surface Temperatures and Durations Associated with Spring Prescribed Fires in Eastern South Dakota Tallgrass Prairies

Fire and grazing are commonly used to manage nonnative grasses in the Northern Great Plains, but the effects of fire frequency and management between fire events on fire behavior in this region are poorly understood. We examined temperature and duration of prescribed spring fires at two locations where plots were treated with two fire frequencies (annual or biennial), simulated grazing (1 mo of weekly clipping in spring) and no simulated grazing. In May 2011 and 2013, soil surface fire temperatures and heat duration were monitored in treatment plots using thermocouples. Probes also were placed at 1, 2, and 3 cm depths to measure soil heat transfer. Lethal heat duration (\u3e60 C) at the surface tended to be longer in plots treated with biennial fires compared to plots treated with annual fires. Fires in 2011 had higher maximum temperatures than 2013. Cooler fires in 2013 were characterized by longer durations of lethal heat. However, simulated grazing increased residence time of lethal temperatures in biennial plots and reduced lethal temperature duration in annual plots. Surface heat did not influence soil temperatures even at the 1 cm depth. Greater fuel loads, characteristic of plots treated with biennial fires, generally were associated with higher maximum temperatures and longer heat durations. Results suggest decreasing fire frequency to once every 2 y, perhaps combined with biennial grazing management, may enhance fire behavior to better meet management objectives