Differences in rainfall interception loss between beech and oak forest stands in a Mediterranean mountain catchment

Canopy interception is a key component of forest hydrology, influencing soil moisture and water availability. This study quantified throughfall and stemflow in beech (Fagus sylvatica) and oak (Quercus robur) stands on opposing slopes within a 44 km2 Mediterranean mountain catchment in central Italy. Over nearly three years, more than 200 precipitation events were monitored in four plots. Relative interception loss averaged 38.7% in oak and 30.6% in beech stands during moderate events. Despite higher canopy cover and leaf area index (LAI) in beech, oak showed greater interception across growing (42.2% vs. 33.2%) and dormant (32.5% vs. 26.0%) seasons. This contrast persisted under leaf-off conditions, when LAI converged between species, indicating that interception is governed by canopy properties beyond leaf area. An adapted LAI-based analytical model systematically underestimated observed losses and failed to reproduce the oak-beech difference. Interception thus emerges from the coupled control of canopy structure and local energy availability.