Stream flow unaffected by Eucalyptus plantation harvesting implicates water use by the native forest streamside reserve

•Hillslope modelling of water dynamics.•Brazilian eucalypt plantation with streamside native forests.•Streamside forests intercepted and used water otherwise resulting in base-flow.•Eucalypt plantation harvesting affected the water table but not stream flow.•Mechanistic simulations were consistent with measurements.

Study regionTropical Atlantic Forest region, Brazil.Study focusThe temporal and spatial dynamics of soil water, water table depth and stream flow in relation to precipitation and the harvesting and regrowth cycle of a Eucalyptus grandis hybrid plantation in a headwater catchment. This landscape contains a mosaic of eucalypt plantation grown for pulpwood on plateau tops and native forest reserves in gullies. Instead of harvesting the native forest to test this effect, we conducted a virtual experiment using a soil and hydrological model (HYDRUS).New hydrological insightsPlantation harvest had little effect on steam flow, despite a 6–11 m rise in water table level under the plantation area. This result suggests that the native forest reserve intercepted groundwater moving laterally between the plantation and the stream. Measured and simulated runoff coefficients were similarly low (5% and 3%, respectively), but simulated removal of the native forest led to an increase to 38%. Therefore, plantation management in this type of landscape is likely to have little impact on stream flows where there is an intact native rainforest reserve beside the stream.