The importance of measuring fire severity—Evidence from microarthropod studies

Fires are considered the most important disturbance regime in many ecosystems, including boreal forest. Fires usually reduce the abundances of soil living animals, but the duration of the fire effect and the recovery rate of soil fauna communities after fire are poorly understood. The species-rich group of microarthropods (collembolans, mites and proturans) constitutes an important part of the soil food-web, contributing to important ecosystem services like decomposition and nutrient mobilization. Recovery rates of microarthropods after fire reported in the literature differ considerable between sites and studies. Here, I examine if variation in fire severity can explain part of the variation in recovery of microarthropods after fire observed among studies. To do so, I have chosen studies done in boreal forests and in which the post-fire situation was described in such a way that fire severity (depth of burn) could be estimated. I also selected studies that used real abundance data and that sampled for animals for at least 2 years after fire.More severe fires were more determinal to soil fauna. Collembola (springtails) recovered within a few years at sites burnt with low severity, but the time frame in most studies (2–5 years) was too short to detect recovery at moderate or severely burnt sites. For mesostigmata and oribatida the recovery patterns were harder to interpret.I argue that fire severity is the most important factor explaining differences in microarthropod responses to fire, and that this is probably true also for other soil dwelling organisms. Because fire severity is often not taken into account when the effects of fire are investigated, generalizations about fire effects are hard to make.