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INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE
Changes in Tree Species in Riparian Zones of Urban Streams May Have
Effects on Restoration and Storm Water Control Efforts.
Research Value:
A riparian zone is the land and
vegetation within and directly
adjacent to surface water
ecosystems, such as lakes arid
streams. The vegetation in
riparian zones provides
ecosystem services to
communities to help them
remain sustainable; services
such as reducing flooding and
bank erosion and reducing
levels of pollutants in streams.
So, a healthy riparian zone
benefits a community
economically by reducing
property damage, increases the
quality of life by providing
more recreational oppor-
tunities for people and habitat
for a diverse community of
terrestrial and aquatic animals,
and helps protect public health
by aiding in pollution control.
Riparian zones are considered
green infrastructure in similar
fashion as things like green
roofs and rain gardens because
they provide the same kind of
ecosystem services.
In cities such as Cincinnati,
OH and Baltimore, MD, tree
species characteristic of
lowland areas have
disappeared from urban
riparian zones and have been
replaced by typical upland tree
species 1>2. This change in
tree species could affect the
riparian zones by making them
less effective at flood control
and at providing quality
habitat for organisms such as
stream fish.
Differences in hydrology and
pollution in urban vs. rural
areas are prime suspects for
this change in tree species
near streams in urban areas.
By sorting out which stressors
are more likely the cause of
this change in species, this
study can provide useful
information to those trying to
preserve and restore riparian
zones in their' communities.
Research Background:
Ozone in srnog at ground level
in the troposphere (as opposed
to the protective ozone layer
in the stratosphere), is a
pollutant that may be
responsible for the
disappearance of some ozone-
sensitive lowland tree species3
in urban areas. Though once
at high concentrations in
smog, ground-level ozone
concentrations have been
lowered in many cities, likely
through EPA-developed
regulations in the Clean Air
Act, first enacted in 1963.
Magnified image of a tree core from
a chestnut oak. Numbers on the
image show the annual rings.
If the shift towards upland
species is due to decades of
high ozone exposure prior to
regulation, then restoring
lowland species to urban
riparian zones may once again
be of hydrologic benefit.
However, if the same species
shift was due to lower water
tables and more severe
droughts in urban areas, then
replanting urban riparian
U.S. Environmental Protection Agency
Office of Research and Development (ORD), National Risk Management Research Laboratory (NRMRL)
Land Remediation and Pollution Control Division (LRPCD)
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zones with lowland species
would not be successful.
By analyzing annual growth
rings of trees to see if patterns
are evident in growth
associated with location or
years, this study may separate
the effects of urban pollution
from persistent hydrologic
changes such as drought.
The growth and species
abundance data from the urban
and rural riparian zones in
Baltimore and Cincinnati will
be used to shed light on the
following question:
What are the roles of
ground-level tropospheric
ozone and urban hydrology
in determining riparian tree
species composition?
Outcomes and Impacts:
Results of this study, which
was begun in 2010, are
expected to be available by
late 2011. When the study is
completed, the results of this
investigation have
implications beyond these two
cities. This research has
potential impact on the
conservation of riparian zones
and storm water management,
both of which are critically
important to communities in
terms of then economies and
public health. This
information can be useful to a
number of community groups
which are already working to
preserve and restore their
riparian zones. Follow-up
studies that expand on the
knowledge gained in this
study are likely as well.
LAND RESEARCH PROGRAM
WEB SITES; www.epa.gov/ord/lrp
www.epa.gov/nrmrl/lrpcd
CONTACTS
Technical Inquiries.
Terry Loecke. 513-569-7730. EPA/
ORD/NRMRL/ LRPCD/ESMB
loecke. teiryfS epa. go v
Communications Inquiries
Roger Yeardley. 513-569-7548.
EPA/ ORD/NRMRL/ LRPCD
yeardley roger ci epa.gov
REFERENCES
1 Groffman PM, et aL (2003) Down by the
riverside: urban npanan ecology. Frontiers in
Ecology and Environment 1:315-321
2. Pennuigtou DN, Hansel JR and Gorchov
DL (2010) Urbanization and npanan forest
woody communities: Diversity, composition.
and structure within a metropolitan landscape.
Biological Conservation 143:182-194
3. Coulston, J. W., G. C. Smith, et al. (2003).
"Regional assessment of ozone sensitive tree
species using bioindicator plants."
Environmental Monitoring and Assessment
83:113-127
National Risk Management Research Laboratory
Land Remediation and Pollution Control Division
EPA/600/F-11/003
April 2011
www.epa.gov/nrmrl
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