Consistent soil organic carbon accumulation under hedges driven by increase in light particulate organic matter

Hedgerow planting is recommended by biodiversity policies and those that promote the inclusion of woody plants in agricultural landscapes to sequester atmospheric carbon into the soil. However, the extent and variability of soil organic carbon (SOC) sequestration under hedges are not known. We measured SOC stock beneath hedges in five pedoclimatic conditions in the UK to quantify the SOC sequestration potential associated with hedgerow planting. We measured SOC stocks in 10 cm intervals in the top 50 cm of soil or to bedrock, comparing 46 hedges of different age classes and their adjacent grassland fields. We assessed how additional SOC stocks and SOC sequestration rates under hedges varied with covariates of climate and soil properties. The mean additional SOC stock under hedges was consistent across pedoclimatic conditions at ∼40 Mg C ha−1 more than improved grassland fields. On average, SOC stocks beneath hedges were 40 % higher than in adjacent fields at 0–50 cm depth, with older hedges storing greater additional SOC stock at depth than younger hedges. The additional stock was driven by an increase in light particulate organic matter (l‐POM), due to increased leaf and root litter inputs under woody vegetation. The mean SOC sequestration rate of mature hedges was 1.5 (1.0–2.0) Mg C ha−1 yr−1 while the net SOC sequestration rates over time since hedgerow planting declined from 4.2 to 0.2 Mg CO2 km−1 yr−1 within the first 20 years. Our results will aid future land-use related carbon accounting and inform climate change mitigation practice.