Soil erosion processes are common in Mediterranean areas due to its climatic conditions, abrupt topography, and its long history of human influence and intensive land management. Forests have a fundamental protective role in combatting soil erosion and land degradation. This research focused on i) assessing soil erosion on forest lands linked to forest variables, and ii) integrating erosion risk into forest management and planning. In more detail, the first goal focused on the relation between erosion occurrence and possible influencing factors such as forest structure and composition, site and land-use characteristics, and, based on this, integrating erosion protection as an objective into multi-functional forest management. The data source was the Spanish National Forest Inventory, which provided erosion records as well as traditional tree and plot measurements. The modelling methods used included classification trees and binary logistic regression analysis. Models were developed for the stand and landscape levels to predict the probability of erosion. Erosion risk was also studied spatially by producing maps based on the predictions of the models. Finally, the models were integrated into a simulation optimisation system in order to assess management alternatives.
The results show that, at the stand level, a higher probability of surface erosion occurrence was strongly related to the forest type and stand structure. For example, sparse stands on slopes in semiarid areas and dense stands with large trees in pure Abies alba and Facus sylvatica forest had higher erosion probability. At the landscape level, a low stand basal area, andisol and cambisol soil types, large size and steep slope of the drainage area, the presence of unpaved roads and increased urban land use resulted in a higher probability of gully erosion. Based on the developed models, erosion protection was used as the management objective in multi-functional forest planning at the stand level, together with timber production and structural diversity. The results demonstrated evident trade-offs between these ecosystem services, depending on the steepness of the slope. The results of this work can help to identify forest areas vulnerable to soil erosion. It provides tools to integrate erosion risk into forest planning, thus enhancing the use of forests in erosion protection in sensitive Mediterranean areas.