The revival of coppicing in Sardinia (Italy): does soil matter?

The growing demand for energy and raw materials, together with climate change and globalization, are predicted to result in increased demand for forest resources in the European countries. The European Union has set an ambitious target to achieve 20 % of energy sourced from renewables by 2020, and biomass is considered among the sources of renewable energy. In this context, the Forest Service of Sardinia (Italy) has recently approved two pilot projects to bring back into use cutting methods in 305 ha of the public forest of Marganai (south Sardinia), over a period of 12 years, and in 375 ha of the public forest of Is Cannoneris (south Sardinia), over a period of 10 years. This study aimed to assess the short-term impact on soil of the coppice-with-standards (CWS) management applied in a Mediterranean holm oak forest, as a contribution to address appropriate recommendations to minimize possible negative effects of the silvicultural practices. For this purpose, soil surface features and topsoil properties were investigated in two representative areas located in the public forest of Marganai and coppiced in the periods November 2012 - March 2013 and November 2011 - March 2012, respectively. The study was conducted through a free survey and a survey by transects, with control plots, combining observations and measurements in the field with laboratory data. Regardless of differences in soils and slope gradient, the same CWS management, in terms of final density of trees standing after the clear-cut and accumulation of brushwood in strips along the maximum slope gradient, was applied in both areas. Field observations and laboratory data highlighted the disturbances caused to the soil by the silvicultural practices in the CWS stands when compared with the undisturbed stands. Statistically, these differences are significant on a 0.05% level. These disturbances were mainly concerning the almost complete removal of organic horizons, with consequent negative impact on organic carbon content, and the activation of erosion processes, mostly related to rainsplash erosion. Although soil mobilization locally largely exceeded the tolerable erosion rates, the absence of extreme rainfall events after the coppicing did not produce critical situations at catchment level. Nevertheless, in large parts of the CWS stands the observed density of vegetation cover does not provide a satisfactory protection against the kinetic energy of raindrops and, consequently, the potential soil erosion risk is still very high. As sustainable forest management should preferentially consider soil and promote its conservation, there is the necessity to adapt the CWS management to local soil, slope, and climatic conditions and to adopt post-harvesting conservation procedures to minimize the negative effects of the silvicultural practices. In this regard, the adjustment of the final density of trees standing after the clear-cut in relation to soil properties, slope gradient, and the possibility of extreme rainfall events, a different brushwood management, and the restriction to the passage of wild animals have to be considered to minimise the negative impacts on soils.