Evaluation of Soil Evolution After a Fire in the Southeast of Spain: A Multiproxy Approach

Fire is considered as part of the ecological dynamic in Mediterranean forests and is strongly related to an anthropogenic origin. The aim of this study is to evaluate the evolution of soil properties after a fire in the short term (20 months) by the use of soil quality indicators. The work is based on a multiproxy approach about three basic aspects: 1) the study of changes in soil properties; 2) the estimation of erosion rates; and 3) the evaluation of colonization evolution by soil arthropods through ichnological analysis. Three sectors were selected for this study: a burned and intervened area, a burned and not intervened area, and a reference area. Soil samples were taken randomly from each plot and their main physico-chemical properties analyzed. The assessment of soil erosion was estimated for each plot from three transects (20 m in length) perpendicular to the maximum slope, and the same transects were used for the ichnological study to identify the different bioturbations and the producers. An increase in pH and K values and C/N ratio, and a decrease in total N, available P, CEC, and respiration rate were observed among the fire-affected areas and the reference area; however, there were no significant differences in soil organic carbon. According to erosion, the hydrological correction measures based on the construction of barriers with trunks and branches favored higher runoff and erosion rates in the intervened areas with respect to the not intervened areas. The ichnological analysis showed that arthropods of Formicidae family and Lycosidae sp. genre were the main organisms that recolonized post-fire scenarios; moreover, a lower ichnodiversity is observed in the not intervened area, although with a greater abundance, with respect to the intervened and reference area. According to our results, 20 months after the fire most soil physical-chemical properties did not experiment significant differences in relation to unburned reference area. Our erosion estimation suggested the hydrological correction measures were not appropriate to reduce erosion rates and led to higher soil losses. Moreover, our ichnological study supports the domination by pioneer and opportunist organisms in the recolonization of burned areas.