Temporal changes in Mediterranean forest ecosystem services are driven by stand development, rather than by climate-related disturbances

The Mediterranean Region constitutes a biodiversity hotspot and its forests have provided multiple ecosystem services (ES) to human societies for millennia. In the last decades, many Mediterranean forests have undergone a decreasing level of direct human pressure and a growing exposure to environmental stress factors (e.g. wildfires and droughts). However, the degree to which these processes have affected the provision of ES remains largely unexplored. We used an extensive database of 3417 permanent plots (period 1990–2015, 25 years) from the Spanish National Forest Inventory in Catalonia (North-Eastern Spain) and a range of four ecological models to measure and estimate changes in five different ES: wild mushrooms production, timber volume increment, water provision, carbon sequestration and erosion mitigation. We then assessed general trends in ES, their spatial–temporal patterns and searched for potential trade-offs in their delivery. Using mixed-effects models, we explored the differences among three biogeographical regions, as well as the effect of different environmental and site level drivers, including descriptors of stand structure and development, the legacies of management practices and disturbances, as well as the influence of historical climate conditions and their recent anomalies. Our results show a general decline of timber volume increment, water provision and carbon sequestration, along with an increase in erosion mitigation across inland and montane regions. Fitted model parameters suggest a predominant role of stand structure in driving changes in forest ES supply in the study area. In particular, stands with high basal areas were associated with steeper declines in most ES, whereas high mean tree diameter generally contributed to ES increases. Finally, our results showed a series of potential trade-offs among temporal changes in ES that were not reflected in exclusively static analyses, highlighting the relevance of including the temporal dimension in regional assessments of ES. Future forest management and planning could better account for overall ES value as well as expected changes in their future provision, paving the way to landscape planning that balances these two essential components of forest ES.