From canopy to creek: A systematic review of the hydrological trade-offs of Mediterranean forest expansion

Study region The Mediterranean region, identified as a global climate change hotspot, faces a critical hydrological paradox: while forest expansion is promoted for carbon sequestration and soil conservation, it potentially threatens water availability in water-scarce catchments. Study focus This article presents a systematic synthesis of peer-reviewed literature (2010–2024) to evaluate the mechanistic trade-offs between Mediterranean forest recovery and hydrological fluxes. Using a PRISMA-compliant protocol, we analysed 59 studies to disentangle the effects of spontaneous reforestation, afforestation, and land abandonment on runoff, infiltration, and evapotranspiration. New hydrological insights for the region The synthesis reveals that forest expansion consistently reduces annual water yield by approximately 20–30% in headwater catchments. This decline is primarily driven by increased interception and transpiration rates that override infiltration gains. Unlike in temperate regions, the "sponge effect" in Mediterranean environments is frequently compromised by high evaporative demand, leading to significant baseflow reductions during summer droughts. However, forests play an irreplaceable role in stabilizing sediment fluxes and buffering flood peaks. The analysis highlights that these hydrological responses are non-linear, scale-dependent, and increasingly amplified by climate warming. We identify a critical gap in current modelling approaches, which often fail to couple dynamic vegetation responses with extreme climatic events. Consequently, we argue that passive reforestation policies must be replaced by adaptive forest management strategies, such as targeted density reduction, to reconcile ecosystem services.