Professor Brigham Young University, Utah, United States
Abstract: Human activities are driving shifts in the size and frequency of wildfires globally. Simultaneously, they are driving transitions in consumer communities, with implications for community resistance to invasive grass invasion. Though the effects of fire and consumer activity are likely important for soil nutrient gradients, very few empirical studies have looked at their long-term impacts. The objective of this study was to understand the main effects and interactions of fire and rodent activity on soil resource availability in arid systems. In a semi-arid desert system, treatment plots were randomly assigned to be burned or unburned as well as rodents allowed or excluded in full factorial design replicated in five experimental blocks. Treatments were imposed in 2011. In 2021, nine soil cores per treatment plot, sampled to a depth of 5 cm, were pooled and analyzed for phosphorus, potassium, organic matter, pH, salinity, nitrate, and ammonium. In plots where shrubs were present, alternating soil samples were taken either within the dripline of shrubs or in intershrub areas, then pooled to account for fertile island effects. Fire increased nitrate by 75% (P=0.0002), phosphorus by 33% (P=0.04), and pH by 1.5% (P=0.08). Rodent activity raised potassium by 27% (P=0.07), pH by 4% (P=0.0002), nitrate by 39% (P=0.02), and lowered organic matter by 14% (P=0.04). The interaction of burning and rodent activity increased phosphorus by 64% above unburned plots where rodents were allowed (P=0.02). This interaction also raised nitrate by 56% over plots burned with rodents excluded (P=0.02), 95% over plots unburned with rodent activity allowed (P=0.0005), and 96% over unburned plots with rodents excluded (P=0.0005). No other direct or interaction effects were found to be significant at this site. We found that rodent activity has large impacts on nutrient availability, particularly in post-fire conditions. As climate change and anthropogenic forces continue to alter fire regimes and rodent communities alike, biogeochemical processes may be greatly altered in arid systems.
