Soil Biological Indicators and Caesium-137 to Estimate Soil Erosion in Areas with Different Forest System Management

In this study, the effects of innovative and traditional thinning on soil properties with respect to unmanaged forest were assessed with the aim to individuate early warning indicators of soil erosion for identifying the most appropriate forestry practices to sustainably manage an Italian beech (Fagus sylvatica) forest. Soil organic carbon (OC), microbial biomass C (MBC), ergosterol (ERG), humification rate, water-soluble phenols (WSP), fluorescein diacetate (FDA) hydrolysis, dehydrogenase (DHA) and catalase activities (CAT), ultrasonic aggregate stability and 137Cs were detected to asses soil health and erosion magnitude. The aim was to correlate 137Cs, as a basic indicator of soil erosion rate, with soil aggregate stability and biological activity parameters. 137Cs results evidenced that both thinning treatments affected soil properties. The innovative treatment showed the highest impact. The amount of small-sized particles enhanced when the intensity of thinning increased. A strong decrease in soil OC was related to thinning. In the upper soil layer, OC was found positively correlated with MBC, FDA, WSP, ERG, C/N, N and also with 137Cs. Moderate to no correlations, in the subsurface layer, highlighted the immediate impact of management techniques on the surface layer and then on the underlying ones. In the subsurface layer, OC maintained its positive correlation only with MBC, WSP and 137Cs. 137Cs was correlated in both soil layers with OC, N and WSP. The overall results suggest that the latter parameters may be considered as indicators of soil erosion. More specifically, WSP can be used, even in the case of the absence of 137Cs in the sediment, to evidence changes in soil properties that could be the starting point of soil fertility loss.