Impacts of arable reforestation on soil carbon and nutrients are dependent upon interactions between soil depth and tree species

Recent interest in temperate farm woodland has focussed on strengthening delivery of ecological and economic benefits from land. However, impacts of temperate farm woodland on soil properties and carbon inventories are poorly studied. With field samples and measurements taken at 35-year-old agroforestry experiment we determine how functioning in three components of the soil column (forest floor, topsoil (0–30 cm) and subsoil (>30 cm)) respond to land-use change, tree species choice and small-scale random variability in soil properties. Tree species influenced soil nutrient dynamics in the forest floor and topsoil, with Hazel forest floor material 27 % less concentrated in phosphorus (P) but containing 50 % more soil organic carbon (SOC) stock than Cherry or Sycamore. Change in land use from arable to woodland controlled soil bulk density, organic matter content and C storage in topsoil, with 15 % (11.8 t ha⁻¹) more SOC stock in 0–30 cm soil beneath woodland compared with arable. In subsoil, tree species and land cover influence over soil functioning was insignificant. Notably, no net difference between arable and woodland soil C storage was found when the 0–50 cm part of the profile was considered as a whole, although net C storage was highly variable by plot. 35 years following planting, soil structure and SOC storage were only different in the forest floor and topsoil compared to the adjacent arable system. Each soil component therefore has its own functioning ‘signature’ in response to afforestation. Future policy support for farm woodland must account for this complexity.