Effects of Repeated Low-Severity Fires on Particle Detachment Capacity and Soil Properties in Rills of Semi-Arid Forests

Abstract

In forest ecosystems, in addition to wildfire hazards, low-severity fires may alter some soil properties and trigger soil erosion, especially on long and steep slopes. The literature on the hydrological effects of fire with variable intensity is ample, but the studies on the post-fire variability of soil detachment capacity in rills (hereafter D_c) are scarce. Moreover, the effects of repeated fires with low severity on the variability of particle detachment have never been evaluated. To fill this gap, this study has explored whether repeated fires influence the rill formation process by measuring D_c on soil samples collected in semi-arid forests of Northern Iran in flume experiments. Fires noticeably increased (up to 45%) D_c over five repeated fires compared to the unburned sites. The effects of fire were always noticeable on almost all soil properties compared to those in the unburned sites. In contrast, its significant impacts on soils with a different number of fires were limited to bulk density, concentrations of some ions, and cation exchange capacity. Therefore, the study suggests proper control of recreational activities in forests and a limit on the burning frequency. Moreover, simple models were set up to estimate the soil erodibility factor and critical shear stress in rills (important input parameters for process-based erosion models) in repeatedly burned soils. D_c was accurately estimated from the stream power or its unit value using linear equations. The stream power provided more reliable predictions (coefficients of the efficiency of Nash and Sutcliffe over 0.75) compared to its unit value. The findings of the study are useful for hydrologists and land managers for erosion prediction and soil conservation tasks, respectively, in delicate forest ecosystems.