Resolving uncertainties in predictive equations for urban tree crown characteristics of the southeastern United States: Local and general equations for common and widespread species: Local and general equations for common and widespread species

Urban forest research and management requires improved methods for quantifying ecosystem structure
and function. Regional equations for urban tree crown width and height can accordingly improve predictions
of urban tree structure. Using a large regional dataset with 12 locations in the southeastern US,
we developed diameter-based equations for 97 urban tree species. Whereas previously published urban
equations have almost exclusively been developed with one location on public or commercial land, our
data included both public and private land uses. For 5 widespread, common urban tree species (Acer
rubrum, Cornus florida, Pinus taeda, Quercus nigra and Lagerstroemia spp.), we also assessed the inclusion
of additional variables such as crown light exposure, land cover, basal area, and location. Overall, height
and crown width models were improved when including additional predictors, although competition
and location effects varied by species. Study city was a significant predictor of tree height in all species
except C. florida, and a significant predictor of crown width for all species except C. florida and Q. nigra. This
indicates that anthropogenically-influenced variation among cities can lead to significant differences in
both tree form and structure and that future model development should utilize data encompassing multiple
cities. Our predictive equations for urban tree crown characteristics provide an improved method
for planning, management, and estimating the provision of ecosystem services to improve quality of life
in cities.