Urban natural areas forest carbon

Urban natural area forests provide cities with crucial ecosystem services,
including carbon storage and sequestration. Although previous work from a
single city has suggested that urban natural area forests may be carbon
rich and dominated by native species, it is unclear if that pattern is
widespread. Indeed, little is known about the species composition and
carbon storage in these green spaces, or how urban natural area forests
compare to similar rural forests. Here, we use data collected by the
Forests in Cities network to quantify carbon stored in urban natural area
forests across 1,852 plots in eight of the most populous US cities and
examine patterns in woody vegetation carbon storage by tree species
composition and size class. We also compare the carbon storage in these
urban natural area forests to similar rural forests using USDA FS Forest
Inventory and Analysis data. We found that urban natural area forests
store between 214-267 Mg C ha-1, with the majority (on average 55%) in the
aboveground portion of live trees and shrubs. This carbon was primarily
stored by native trees and increased with the proportion of native
species, as native trees tended to be larger. The proportion of nonnative
species was higher in smaller size classes. Overall, the woody vegetation
carbon density in urban natural area forests was higher than similar
forest types in rural settings, a phenomenon driven by the presence of
more large trees. Synthesis and Applications Together these results
demonstrate the importance of urban natural area forests as carbon-dense
ecosystems and havens for native tree species. However, because of the
greater number of non-native species in smaller size classes, these
forests may also be at risk of transitioning away from native-dominated
systems. Therefore, greater monitoring efforts and increased management
activities such as non-native species removal will be crucial to
maintaining the high carbon storage and health of these
ecosystems.