Biomass pools in intensively managed hedgerows can be a net emission of carbon dioxide

Perennial landscape features, such as hedgerows, can play a role in enhancing terrestrial carbon (C) sinks, especially in North-western Europe, where they form a large part of the agricultural landscape. To date, there are few studies relating aerial imagery to ground-truthed biomass measurements and relating changes in biomass to hedgerow management. This study sought to develop relationships between measured biomass of hedgerows and digital elevation model (DEM) data from drones and aircraft. Furthermore, changes in hedgerow above-ground and below-ground biomass stocks were assessed using a two-point sampling approach. The developed inventory framework was then applied to a pilot study area of 419,701 hectares in Ireland. Robust relationships were developed relating DEM data to volume and above-ground biomass. Model equations were also developed linking above-ground and below-ground biomass. However, these were less robust due to the confounding impact of hedgerow management. Aboveground biomass was linearly correlated with hedge volume with irregular, unmanaged hedgerows observed to contain significantly higher amounts of aboveground biomass compared to regular, highly managed hedgerows. When the models were extrapolated to the county level, hedgerow biomass C pools are suggested to be a net emission of -0.3 tC. ha-1.yr -1 due to removals and management.