Organic carbon storage in the biomass and soils of hedgerows

The establishment of hedgerows as traditional form of agroforestry in Europe is a promising strategy to promote carbon sinks in the context of climate change mitigation. However, only few studies quantified the potential of hedgerows to sequester and store carbon. We therefore conducted a meta-analysis to gain a quantitative overview about the carbon storage in the above- and below-ground biomass and soils of hedgerows.

Soil organic carbon (SOC) data of hedgerows and adjacent agricultural fields of nine studies with 83 hedgerow sites was compiled. On average, the establishment of hedgerows on cropland increased SOC by 32%. No significant differences were found between the SOC storage of hedgerows and that of grassland. The literature survey on the biomass carbon stocks of hedgerows resulted in 23 sampled hedgerows, which were supplemented by own biomass data of 49 hedgerows from northern Germany. Biomass stocks increased with time since last coppicing and hedgerow height. The mean (± SD) above-ground biomass carbon stock of the analysed hedgerows was 48 ± 29 Mg C ha^-1. Below-ground biomass values seemed mostly underestimated, as they were calculated from above-ground biomass via fixed assumed root:shoot ratios not specific for hedgerows. Only one study reported measured root biomass under hedgerows with a root:shoot ratio of 0.94:1 ± 0.084. With this shoot:root ratio an average below-ground biomass carbon stock of 45 ± 28 Mg C ha^-1 was estimated, but with high uncertainty.

Thus, the establishment of hedgerows on cropland could lead to a SOC sequestration of 1.0 Mg C ha^-1 year^-1 over a 20-year period. Additionally, up to 9.4 Mg C ha^-1 year^-1 could be sequestered in the hedgerow biomass over a 10 year period. In total, hedgerows store 106 ± 41 Mg C ha^-1 more C than croplands. Our results indicate that organic carbon stored in hedgerows is similar high as in forests. We discuss how the establishment of hedgerows, especially on cropland, can thus be an effective option for C sequestration in agricultural landscapes, meanwhile enhance biodiversity, and soil protection.