Disturbance Caused by Animal Logging to Soil Physicochemical and Biological Features in Oak Coppices: A Case-Study in Central Italy

Abstract

Firewood extraction by mule forwarding is still common in oak coppices in Central and Southern Italy. This is due to the scarce presence of aerial extraction systems such as cable yarders. Considering the importance of forest soil for all ecosystem services, the evaluation of the disturbance that a given extraction system has on the forest soil is a fundamental aspect in the framework of sustainable forest management. Therefore, this study was developed to assess the disturbance caused to the physicochemical and biological features of soil and to coppice after mule logging according to the standards of silvicultural treatment, as well as the recovery time needed after the logging intervention. Four cutting blocks located in Central Italy represented the study area, one cutting block represented the unharvested control, while the others were logged 3 years (CB-2019), 8 years (CB-2014) and 10 years (CB-2012) prior to the field surveys. In each harvested cutting block the soil was subdivided into disturbed soil (DIST—mule trails) and low disturbance soil (LD—area within the harvested cutting block not affected by mule passage). This experimental design assessed the disturbance caused by logging operations by mules (DIST soil) and the silvicultural treatment (LD soil) to soil physicochemical (bulk density, penetration resistance, shear resistance, and soil organic matter) and biological properties (soil microarthropod community evaluated with the QBS-ar index). The results revealed a significant disturbance in the mule trails for all the investigated variables. The disturbance was particularly strong for the QBS-ar index, with values which were lower than half of those of the control area. Furthermore, no recovery process was evident even after 10 years from the logging interventions. Instead, values of the various parameters became worse with time after harvesting. On the other hand, no marked disturbance was revealed in LD soil, except for a significant decrease in soil organic matter. Although this is a preliminary evaluation that needs to be confirmed with further study, this trial suggested that mule logging cannot be considered a fully low-impact approach to forest operations and that studies with a longer time span after harvesting are needed to assess the recovery process in the mule trails.