The future urban forest: a survey of tree planting programs in the Northeastern United States

Cities around the world are pursuing tree planting as a way to increase
tree cover. Despite the growing interest in planting trees as a way to
offset climate change, counter the negative impacts of urbanization, and
provide benefits to city dwellers, there has not been a recent effort to
quantify the number of trees being planted nor the species composition of
these plantings. Because ecosystem services and ecosystem threats can
transcend municipal boundaries, understanding trends in tree planting at
multiple spatial scales is critical. To overcome this knowledge gap, we
used a survey to collate recent tree planting data from 52 cities with
populations greater than 50,000 people in the Northeastern USA. The four
largest cities in our study (New York, Boston, Philadelphia, Washington
D.C.) planted over 87% of all the trees that were planted in the region.
Smaller cities, which are numerous in region, planted proportionally fewer
trees and, in over 40% of the small cities surveyed, planting palettes
included invasive tree species, highlighting both a resource and knowledge
gap in smaller cities as compared with larger ones. Regardless of city
size, records also illuminated an overreliance on certain genera for
specific ecosystem services; nearly 20% of all shade trees were Quercus
species and over 40% of ornamental trees were either Syringa or Prunus
species. As cities continue to rely on tree-planting as a form of green
infrastructure, our results demonstrate that more consideration to
establishing diverse planting palettes will be an important way to ensure
that ecological resilience is maintained. Achieving this will depend on
increased opportunities to collaborate across municipal boundaries and
promoting cross-learning from the experiences of more innovative urbanized
regions to urban regions with less infrastructure and expertise.