Hedgerows are a traditional form of agroforestry in the temperate climate zone. The establishment of hedgerows may be a promising strategy to promote carbon (C) sinks for climate change mitigation. We therefore conducted a meta-analysis compiling data from 83 sites on soil organic carbon (SOC) stocks beneath hedgerows in comparison with adjacent croplands and grasslands, plus biomass data from 64 hedgerows. On average (± SD), the establishment of hedgerows on cropland increased SOC stocks by 32 ± 23 %. No significant differences were found between the SOC stocks of hedgerows and those of grassland. The average above-ground biomass stock was 47 ± 29 Mg C ha−1. Only one study reported measurements of below-ground biomass stocks and root/shoot ratios. Based on these measurements, an average below-ground biomass stock of 44 ± 28 Mg C ha−1 was estimated, but with high uncertainty. In total, hedgerows were estimated to store 104 ± 42 Mg ha−1 more C than croplands, with biomass contributing 84 % (87 ± 40 Mg C ha−1) and soil 16 % (17 ± 12 Mg C ha−1) to this amount. Total C sequestration with the establishment of hedgerows on cropland could be between 2.1 and 5.2 Mg ha−1 year−1 for a period of 50 and 20 years, respectively. Our results indicate that C stocks in hedgerows are on average comparable to estimates for forests. The establishment of hedgerows, especially on cropland, can therefore be an effective option for C sequestration in agricultural landscapes while enhancing biodiversity and soil protection.

Background Soil organic carbon (SOC) storage is highly variable across sites and primarily depends on site properties and land use. It is therefore difficult for farmers to evaluate the actual SOC status of a site. To aid the interpretation of measured SOC contents, easy‐to‐use frameworks for the assessment of SOC contents are needed. Aims The aim of this study was to derive site‐specific SOC benchmarks for German mineral soils under agricultural use based on the dataset of the first German Agricultural Soil Inventory. Methods The dataset was stratified into 33 strata by land use, soil texture, C/N ratio and mean annual precipitation. Lower and upper SOC benchmarks were calculated for all strata (0.125 and the 0.875 quantile). Results The SOC benchmark value ranges were lower for cropland (6.8–48.9 g kg–1) than for grassland (14.1–76.6 g kg–1), and increased with rising clay content and precipitation. Sandy soils with a wide C/N ratio and high SOC content due to their heathland or peatland history were divided into separate strata. The number of strata only decreased the SOC benchmark ranges slightly. Around 15–20 sites were required as a minimum to quantify SOC benchmarks for one stratum. Conclusions The presented framework is easy to use, requiring only four readily available stratification factors to perform a comparative classification of SOC contents. It allows farmers and extension services to compare where their measured SOC contents fall within the expected SOC value range for their site, and can thus help develop an initial evaluation of the SOC status of a site with regard to soil‐specific differences.

<p>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.</p><p>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<sup>-1</sup>. 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<sup>-1 </sup>was estimated, but with high uncertainty.</p><p>Thus, the establishment of hedgerows on cropland could lead to a SOC sequestration of 1.0 Mg C ha<sup>-1</sup> year<sup>-1</sup> over a 20-year period. Additionally, up to 9.4 Mg C ha<sup>-1</sup> year<sup>-1</sup> could be sequestered in the hedgerow biomass over a 10 year period. In total, hedgerows store 106 ± 41 Mg C ha<sup>-1</sup> 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.</p>