Fire differentially affects soil properties of forests and grasslands: A global meta-analysis

Abstract

Fire is one of the most frequent disturbances in ecosystems, exerting profound effects on soil structure and nutrient dynamics. However, its impact on soil physical, chemical, and biological properties and the differences in soil responses to fire between forests and grasslands at a global scale have not been systematically evaluated. To address this gap, we constructed a global database of fire-induced soil changes, which includes data from 253 studies (1,896 observations of grassland soil properties and 3,425 observations of forest soil properties). We found that, globally, fire increased soil bulk density (BD), pH, and available phosphorus (AP) by 1.1–17.9 %, while it decreased soil water content (SWC), mean weight diameter (MWD), soil respiration (SR), soil total carbon (TC), total nitrogen (TN), soil organic matter (SOM), and the C/N ratio by 3.7–22.9 %. In forests, soil properties were more strongly affected by fire compared to grasslands, with effect sizes 1.02–32.0 times greater, except for soil potassium and magnesium, which exhibited contrary changes. Variation partitioning indicated that fire-induced soil changes in forests were explained by geoclimatic conditions (72.1 %) and fire characteristics (24.3 %), whereas in grasslands, the soil changes were predominantly explained by fire characteristics (79.1 %) rather than geoclimatic conditions (15.4 %). Path analysis revealed that post-fire time, mean annual precipitation (MAP), and mean annual temperature (MAT) increased the soil effect sizes in forests, with coefficients of 0.06, 0.09 and 0.08 (p < 0.05), respectively. Conversely, in grasslands, post-fire time and fire intensity directly decreased soil effect sizes, with coefficients of −0.13 and −0.06 (p < 0.05), respectively. These findings highlight the differences in the response of soil properties to fire between forests and grasslands, determined by climate factors and fire characteristics. Our resulets advance the mechanistic comprehension of differential responses in soil properties to fire in global forest and grassland ecosystems, particularly in the context of climate change and the escalating frequency of fire disturbances.