The effect of fire disturbance on the dynamics of soil physical, chemical, and biological properties over time in a semi-arid region

Fire has important effects on soil properties and functioning in terrestrial ecosystems that have been explored by many studies. Limited information exists on the alterations in soil parameters over time caused by fire disturbance in semi-arid climates. This study is designed to examine the influence of fire disturbance on the change of soil physical, chemical, and biological properties over time in a semi-arid region. In the summer of 2007, a severe natural fire occurred in the Pideh region of northern Iran, dominated by hawthorn (Crataegus melanocarpa M.B.) and berberis (Berberis integerrima Bunge), which destroyed almost 80 % of the shrubs and the majority of the co-dominant plants over a vast area. For this research, 12 soil samples (0-10 cm depth) were taken in summer (August) in different years (i.e., 2010, 2013, 2016, 2019, and 2022) from the burnt area. Furthermore, a total of 12 soil samples were collected during the summer (August) of 2022 from unburned regions to serve as a control. Soil biological parameters were studied by conducting soil samplings in the summer (August) and autumn (November) of every year. To evaluate soil N mineralization, soil samplings were done in summer (August and September) and autumn (November and December). Our results indicated that the occurrence of fire increased soil bulk density, with a concomitant decline in soil organic matter (SOM), porosity, aggregate stability, particulate organic carbon and nitrogen (POC and PON), as well as available nutrients such as ammonium (NH4+) and nitrate (NO3-) levels. Additionally, microbial parameters (respiration and biomass) and enzymes (urease, acid phosphatase, arylsulfatase and invertase), experienced a decrease in areas affected by the fire over time of 2010 to 2022. Unburnt (2022) and burnt (2022) sites had higher density and biomass of the three earthworm groups. Acari, Collembola, nematodes, protozoans, fungi and bacteria were significantly affected by fire disturbance in the different seasons, and years, and declined in the order unburnt sites > burnt sites 2022 > burnt sites 2019 > burnt sites 2016 > burnt sites 2013 > burnt sites 2010, respectively. Fire has complex effects on soil, involving interactions among physical, chemical, and biological properties that may persist for a prolonged period. After fifteen years of fire disturbance, soil characteristics were different in the burned (2022) and unburned areas. This research offers valuable insights into the impact of fire on soil characteristics over time, as well as a comparison with an unburned area. Therefore, it is essential to adopt soil management practices to minimize soil disruption in burned areas and facilitate the full recovery of soil ecosystems after fire damage.