Global carbon cycle patterns of trees in the city: a meta-analysis

Keywords: climate change, urban trees, carbon sequestration, carbon emissions
Session Type: Virtual Paper Abstract
Day: Friday
Session Start / End Time: 2/25/2022 09:40 AM (Eastern Time (US & Canada)) - 2/25/2022 11:00 AM (Eastern Time (US & Canada))
Room: Virtual 39

Abstract

Our understanding of carbon cycles of trees in urban landscapes has been rapidly advanced over the last decade through many tree surveys in cities worldwide. We conducted a meta-analysis to synthesize global patterns in urban tree carbon storage (and sequestration) at the landscape scale, i.e., Mg Cꞏha-1 (ꞏy-1). We included data from 154 cities representing 34 countries across the climatic range of urbanization globally. Despite differences in magnitudes within and among cities, a unifying log-linear relationship between storage and sequestration was observed indicating greater tree carbon densities had lower sequestration rates as a proportion of standing tree carbon. Sequestration rates by urban trees (i.e., urban trees NPP) were positively correlated with reference net primary productivity (reference NPP; derived based on climate in the absence of urbanization). The response of urban trees, though, was flattened: only a 12% increase in urban trees NPP per unit increase in reference NPP. The flattening effect of urbanization on climate gradients in NPP could in part be organized through limiting resource gradients. Urban trees NPP were 4-8 Mg Cꞏha-1ꞏy-1 less than reference NPP in wetter climates to almost no difference in extremely arid climates. Assuming a global carbon sequestration rate of 1 Mg Cꞏha-1ꞏy-1 based on findings here and an estimated range in global urban land extent of 100-300 Mha, urban trees are a potential carbon sink of 1-3% of global carbon emissions (0.1-0.3 Pg C sequestered of 9.7 Pg C emitted in 2020).