Afforestation, as one of the major drivers of land cover change, has the potential to provide a wide range of ecosystem services. Aside from carbon sequestration, afforestation can improve hydrological regulation by increasing soil water storage capacity and reducing surface water runoff. However, afforested areas are rarely studied over time scales appropriate to determine when changes in soil hydrological processes occur as the planted (mixed) forests establish and grow. This study investigates the seasonal soil moisture and temperature dynamics, as well as the event‐based responses to precipitation and dry periods, for a mature and a juvenile forest ecosystem over a 5‐year time period. Generally, soil moisture was higher in the juvenile forest than in the mature forest, suggesting a lower physiological water demand. Following the 2018 drought, soil moisture dynamics in the growing juvenile plantation began to match those of the mature forest, owing to canopy development and possibly also to internal resilience mechanisms of the young forest to these external hot weather perturbations. Soil temperature dynamics in the juvenile plantation followed air temperature patterns closely, indicating lower thermal regulation capacity compared to the mature forest. While our findings show that an aggrading juvenile plantation achieves mature forest shallow soil moisture storage dynamics at an early stage, well before physiological maturity, this was not the case for soil temperature. Our results shed light on long‐term trends of seasonal and event‐based responses of soil moisture and temperatures in different‐aged forest systems, which can be used to inform future assessments of hydrological and ecosystem responses to disturbances and forest management.

The ecosystem services provided by forests modulate runoff generation processes, nutrient cycling and water and energy exchange between soils, vegetation and atmosphere. Increasing atmospheric CO 2 affects many linked aspects of forest and catchment function in ways we do not adequately understand. Global levels of atmospheric CO 2 will be around 40% higher in 2050 than current levels, yet estimates of how water and solute fluxes in forested catchments will respond to increased CO 2 are highly uncertain. The Free Air CO 2 Enrichment (FACE) facility of the University of Birmingham's Institute of Forest Research (BIFoR) is the only FACE in mature deciduous forest. The site specializes in fundamental studies of the response of whole ecosystem patches of mature, deciduous, temperate woodland to elevated CO 2 (eCO 2 ). Here, we describe a dataset of hydrological parameters – seven weather parameters at each of three heights and four locations, shallow soil moisture and temperature, stream hydrology and CO 2 enrichment – retrieved at high frequency from the BIFoR FACE catchment.