been less extensively explored, although urban plant
and bird biodiversity are found to be greater in high-
er-income neighborhoods.
Urban bird diversity follows
HOLC grades, with bird species composition today being
well-predicted by race-based zoning from 80 years ago,
but diversity of other plants and animals in relation to
historic HOLC grades have been relatively unexplored.
Our analysis in Baltimore was led by researchers
from the
University of Maryland College Park, Johns
Hopkins University, the USDA Forest Service, and the
University of Maryland Baltimore County. We used
a 2018 street tree inventory, which included vacant
potential tree locations in addition to existing live
and dead trees, to calculate street tree occupancy
rates by neighborhood. We also analyzed existing
trees by size class to reflect past (larger trees) and
current (small trees) investment in the urban forest.
Implications
Our findings have implications for ecosystem services
across the city of Baltimore. Redlined neighbor-
hoods were locations of recent tree planting activities,
with a high occupancy rate of small (young) trees.
However, the community composition of these young
trees in D-graded neighborhoods was more likely to
be dominated by fewer tree species within a neigh-
borhood, particularly red maple (Acer rubrum).
A lack of larger trees suggests lower rates of ecosystem
service provision, from cooling effects to carbon storage
to stormwater capture. In addition, a less diverse urban
forest may be less resilient to pest and disease out-
breaks and support
less biodiversity of insect herbivores
and the arthropods and birds that feed on them. As a
result, residents of redlined neighborhoods may receive
fewer ecosystem services now and, depending on their
resilience, may be in jeopardy of losing the continued
provision of critical ecosystem services into the future.
Overall, while the negative effects of redlining remain
detectable in present-day street tree communities, there
are clear signs of recent investment in Baltimore. The city
has sustainability goals of increasing tree canopy cover to
40% by 2040 and increasing overall levels of biodiversity.
Our results regarding small (young) trees in D-graded
neighborhoods may reflect the tree canopy goal and
the City's work to address tree inequities through its
TreeBaltimore initiative. Decisions on which trees to
plant where are complex, involving both top-down deci-
sions by TreeBaltimore and private developers, as well as
bottom-up actions by contracted organizations that are
planting trees limited by what species they can access. >>
For biodiversity experts, street trees provide
a unique study population because trees
can live for many decades, and patterns of
street tree size, distribution, and diversity
reflect both present-day and historical
public policy and management decisions.
30 CityTREES
