Additional soil organic carbon stocks in hedgerows in crop-livestock areas of western France

Abstract Mitigating climate change is a critical challenge, and establishing agroforestry systems is identified as an effective strategy to increase carbon (C) sequestration in agricultural areas. However, the C storage potential of agroforestry systems, especially hedge agroforestry, still needs to be quantified in temperate areas. This study was performed in three mixed crop-livestock areas of western France and focused on hedges planted 20 years ago and on hedges inherited from the traditional hedge landscape and planted 40−120 years ago. We quantified soil organic carbon (SOC) stocks to a depth of 90 cm in 21 agricultural fields adjacent to a hedge, at 1, 3, 6 and 18 m from the hedge. Additional SOC storage by hedges were estimated in comparison to a reference plot, which corresponded to the 18-m measurement. SOC storage dynamics was empirically modeled from the measurements. SOC distribution by particle-size fraction at 0−30 cm depth was also measured. Compared to those in a reference plot, SOC concentrations and stocks were significantly higher in the adjacent field up to 1 m from the hedge at 0−60 cm depth, and up to 3 m from the hedge at 60−90 cm. However, 56–65 % of the additional SOC was stored at 0−30 cm depth and within 1 m of the hedge. Additional SOC stocks equaled 30−50 % of the C stored in non-harvested biomass. Estimates of SOC accumulation rates over 30 years after tree planting ranged from 0.034−0.096 Mg C yr−1 per 100 linear m of hedge. In the first 30 cm, 59–85 % of the additional SOC was stored in the labile particulate organic matter fraction. Our study demonstrated hedges’ significant potential to store SOC locally around themselves; combined with other practices to store C, they could help increase C storage potential at the scale of an agricultural landscape. Results also highlight the high variability in hedge storage potential, depending on hedge characteristics and intrinsic soil properties, whose underlying controlling processes remain to be understood.