Recurring surface fires cause soil degradation of forest land: A simulation experiment with the EFIMOD model

Renewal of pine forests is ecologically dependent on fires, but if fires become too frequent, they can disrupt the equilibrium and sustainability of these ecosystems. Field studies of the effects of fire are challenging because of the heterogeneity of forest ecosystems and because of the heterogeneous effect of fire on recovery of vegetation. As an alternative to complex field studies, mathematical models can be used as a tool to assess the complex dynamics of natural ecosystems as they recover after fire. The aim of this study was to apply the ecosystem model EFIMOD to analyse the effect of surface fires on soil degradation and its feedback on tree productivity in Scots pine forests on different soil types in Russia: Haplic Podzols in the Leningrad region and Psamment Entisols of the fragmented steppe in the Samara region. Simulation of the cumulative effects of fire cycles over 140years showed that one fire did not affect growing stock but decreased soil organic matter by about 10% at both sites, and that three fires reduced the growing stock by 30% on the Haplic Podzols and 9% on the Psamment Entisols and decreased soil organic matter by about 30% on both sites. Forest fires led to the loss of soil carbon (C), as well as nitrogen (N), which is a principal limiting factor in forest ecosystems of boreal and temperate ecozones. The effect of repeated fire cycles on land degradation is similar to that of soil erosion, through the loss of soil C and N.