The role of wildfire on soil quality in abandoned terraces of three Mediterranean micro-catchments

Abstract

Wildfire in abandoned terraces represents a challenge of land management and soil protection in the Mediterranean region due to afforestation of former agricultural land is a major driving force in changing fire regimes and hence land degradation. The effects on physicochemical and biological parameters caused by wildfires on abandoned terraces and non-terraced soils were investigated in three Mediterranean micro-catchments. The study areas were set up as follows: (i) unburned and non-terraced, (ii) unburned and terraced, (iii) once burned and non-terraced, (iv) once burned and terraced, (v) twice burned and non-terraced and (vi) twice burned and terraced. In each of these areas, six composite soil samples 0-15 cm depth were collected from representative plots (25 m2). The results revealed that the best soil quality related with microbiological activity occurred in the unburned and non-terraced plots. However, burned terraced sites, whether burned once or twice, showed significantly higher values of C/N ratio than unburned and non-terraced plots. The nutrient content (magnesium, sodium and potassium) was not affected by wildfire whereas terracing significantly altered the base cation content. Soil enzyme activity correlated positively with the basal soil respiration (REB) rates and carbon content (correlation coefficients ranged from 0.80 to 0.85), but correlated negatively with the C/N ratio (correlation coefficients ranged from −0.37 to −0.47). Even a long time after abandonment (>50 years), soils in terraced plots did not reach the soil quality status of non-terraced and unburned plots. These data suggest significant soil degradation generated by wildfires frequency in abandoned terraces.