Identifying potential sources of variability between vegetation carbon storage estimates for urban areas

Although urbanisation is a major cause of land-use change worldwide, towns and cities remain relatively understudied ecosystems. Research into urban ecosystem service provision is still an emerging field, yet evidence is accumulating rapidly to suggest that the biological carbon stores in cities are more substantial than previously assumed. However, as more vegetation carbon densities are derived, substantial variability between these estimates is becoming apparent. Here, we review procedural differences evident in the literature, which may be drivers of variation in carbon storage assessments. Additionally, we quantify the impact that some of these different approaches may have when extrapolating carbon figures derived from surveys up to a city-wide scale. To understand how/why carbon stocks vary within and between cities, researchers need to use more uniform methods to estimate stores and relate this quantitatively to standardised 'urbanisation' metrics, in order to facilitate comparisons. -- Highlights: • Broad-scale spatial data fail to capture the fine-grained urban landcover mosaic. • This can have a large impact when extrapolating carbon densities up to a city-wide value. • We review how methodologies to estimate vegetation carbon vary in the literature. • We need a more uniform method for estimating carbon stores to aid inter-city comparisons. • This will allow the drivers underpinning urban carbon stock variability to be identified. -- As variability between urban vegetation carbon storage estimates is becoming increasingly apparent, we examine potential methodological drivers that may be responsible, and illustrate why a more consistent approach to biological carbon accounting would be beneficial