Assessment of post-wildfire soil quality and its recovery in semi-arid upland rangelands in Central Iran through selecting the minimum data set and quantitative soil quality index

Recovery of soil quality after wildfire is essential for soil functioning such as nutrient cycling, resistance to biochemical degradation and sustainable plant growth. Post-fire soil quality is crucial for the maintenance of ecosystem sustainability. The objective of this study was to develop a soil quality index (SQI) for assessing post-fire soil quality in upland rangeland ecosystems of a semi-arid region in Central Iran. Soil samples were collected from burnt and unburnt plots at six rangeland sites two years after a wildfire event and analyzed for 22 soil properties. The soil microbial and biochemical properties indicated a greater magnitude of post-fire changes than soil chemical properties. The contribution of microbial respiration to soil quality, obtained using factor analysis, was the highest (36%) followed by particulate organic carbon (22%), microbial biomass carbon (15%), available phosphorus (15%) and alkaline phosphomonoesterase activity (12%). This indicates that microbial properties, labile carbon and phosphorus availability are the most important soil quality indicators to detect the wildfire effects in the study rangelands. The SQI value was, on average, 28% lower in burnt rangelands (0.39-0.55) than unburnt rangelands (0.56-0.75); indicating disturbance by wildfire would be accompanied by the loss of soil functioning. This illustrates that fire decreased soil quality, which did not recover two years after fire, probably due to the high grazing pressure and climatic conditions (i.e., longer drought periods and water limitation). Apparently, a longer period of time would be required for the complete recovery of soil quality in these semi-arid rangelands. In this study, we demonstrate that an integrated SQI would be more useful to assess post-fire soil functions than single soil properties in fire-affected rangelands of semi-arid climates.

Automated summary

The study aimed to develop a soil quality index for assessing post-fire soil quality in upland rangeland ecosystems, highlighting that microbial properties, labile carbon, and phosphorus availability are crucial indicators of wildfire effects. The research showed a significant decrease in soil quality in burnt rangelands compared to unburnt ones, with soil quality not fully recovering even two years after the fire, likely due to high grazing pressure and climatic conditions.