The impacts of a wildfire in a semiarid grassland on soil nematode abundances over 4 years

Fire is the most common disturbance in arid regions and is expected to become more common in many areas as a result of climate change. In this study, I followed the impacts of a wildfire on soil nematode abundances and soil moisture and organic matter (SOM) content in a semiarid grassland for 4 years, using paired burned and unburned sites. I also used a laboratory microcosm experiment to determine the capacity of nematodes to recover under favorable conditions and the importance of surface litter in their recovery. Immediately following the fire, bacterivorous, fungivorous, and herbivorous nematodes in burned sites were 49, 73, and 76% less abundant than in unburned reference sites. Although microbivores recovered rapidly in the microcosm experiment, this recovery was dependent on surface litter, which was reduced by 86% in burned sites in the field. The recovery of microbivores took more than 3 years in the field, and herbivores did not recover during the study period. It is not clear why herbivores did not recover in the field, given that plants seemed to, but it may be related to longer generation times or slower dispersal. Burned sites also had 22% less SOM than unburned sites over the study period and lower soil respiration and pH 14 and 21 months, respectively, after the fire. Soil moisture was lower in burned sites for at least 14 months. The slower recovery of nematode abundances in the field, compared to microcosms, may be related to the exacerbation of moisture limitation at burned sites in this semiarid region. Changes in fire regime may, therefore, have widespread impacts on soil food webs and processes in semiarid climates.