Intra- and interspecific variations of tree allometry in rural and urban settings

Source abstract

Carbon sequestration and storage by trees is a globally important nature-based approach to climate mitigation. However, uncertainties in the application of structural and mass allometric measures to estimate aboveground biomass within trees considerably impacts confidence in quantifying estimates of their resulting carbon store. This is compounded for trees within urban settings where environmental and management context may exert considerable influence over tree form, function and resulting biomass or carbon storage. This study examines allometric relationships and biomass distribution for two common urban tree genera ( Quercus spp., Acer spp .). Single tree terrestrial laser scans collected from 40 trees in urban park settings in Manchester, UK are compared to TLS data collected from both rural hedgerow (n = 39) and closed canopy woodland (n = 580). Adopting a consistent processing workflow enables direct comparison between structural and mass allometries of trees in each setting. Urban trees exhibit distinct structural patterns compared to rural counterparts, interpreted to reflect both broad environmental context and species-specific sensitivity to urban stressors such as soil compaction and water availability. We find no consistent evidence to suggest that urban tree management has a significant impact on structural allometries within our datasets. Aboveground biomass in urban trees is found to be lower than rural equivalents for a given DBH, with notable shifts in allocation toward branches. Standard, widely-used mass allometric models overestimate aboveground biomass in urban settings - by up to 79% - underscoring the need for modified or context-specific allometries for urban biomass and carbon inventories. We suggest that urban tree aboveground biomass and carbon stock estimates may therefore be considerably inflated. As such, we conclude that urban planning targets relying on urban trees for climate mitigation should increase canopy cover goals accordingly to meet carbon sequestration and storage ambitions.