Mapping an urban ecosystem service: quantifying above‐ground carbon storage at a city‐wide scale

1. Despite urbanization being a major driver of land‐use change globally, there have been few attempts to quantify and map ecosystem service provision at a city‐wide scale. One service that is an increasingly important feature of climate change mitigation policies, and with other potential benefits, is biological carbon storage. 2. We examine the quantities and spatial patterns of above‐ground carbon stored in a typical British city, Leicester, by surveying vegetation across the entire urban area. We also consider how carbon density differs in domestic gardens, indicative of bottom‐up management of private green spaces by householders, and public land, representing top‐down landscape policies by local authorities. Finally, we compare a national ecosystem service map with the estimated quantity and distribution of above‐ground carbon within our study city. 3. An estimated 231 521 tonnes of carbon is stored within the above‐ground vegetation of Leicester, equating to 3·16 kg C m−2 of urban area, with 97·3% of this carbon pool being associated with trees rather than herbaceous and woody vegetation. 4. Domestic gardens store just 0·76 kg C m−2, which is not significantly different from herbaceous vegetation landcover (0·14 kg C m−2). The greatest above‐ground carbon density is 28·86 kg C m−2, which is associated with areas of tree cover on publicly owned/managed sites. 5. Current national estimates of this ecosystem service undervalue Leicester’s contribution by an order of magnitude. 6. Synthesis and applications. The UK government has recently set a target of an 80% reduction in greenhouse gas emissions, from 1990 levels, by 2050. Local authorities are central to national efforts to cut carbon emissions, although the reductions required at city‐wide scales are yet to be set. This has led to a need for reliable data to help establish and underpin realistic carbon emission targets and reduction trajectories, along with acceptable and robust policies for meeting these goals. Here, we illustrate the potential benefits of accounting for, mapping and appropriately managing above‐ground vegetation carbon stores, even within a typical densely urbanized European city.