FORESTED WETLANDS IN URBANIZING LANDSCAPES
Mark T. Brown1
Abstract.-While the direct conversion of wetlands to urban and agricultural uses in Florida has been
reduced in the past decade, there has been a noticeable decline in quality of wetlands throughout areas of rapid
urbanization. This is attributed to changes in environmental conditions like hydrologic and nutrient regimes
resulting from development of the surrounding landscape. A classification of wetlands using landscape position,
nutrient access, and hydrologic regime is introduced and related to sensitivity to change. Successional phasing
and timing may be modified as the result of changes in hydrologic and nutrient regimes. Suggestions are given
for landscape scale management that might reverse current trends of wetland loss resulting from cumulative
alteration of the landscape.
There is no question that wetlands are an important
component of the landscape mosaic. Their habitat value, their
role in nutrient dynamics, and their value as water detention
systems have been alluded to by many individuals in a
variety of publications. As a result, there has been increasing
attention paid to protecting wetland ecosystems and
preserving their important functions.
The State of Florida, through its "Wetlands Protection
Act of 1984" (17.12 Florida Statutes) and the rules that were
promulgated as a result, have all but stopped the conversion
of wetlands into urban land uses and have greatly reduced
their conversion into agricultural uses. The five regional
water management districts and numerous local governments
throughout Florida have developed policy and regulations
protecting isolated wetlands that were not under State
jurisdiction and have, all but eliminated the conversion of
these important wetlands. Estimates using U.S. Fish and
Wildlife Service data suggest that between 1900 and the end
of the 1970's nearly 1.5 million hectares of wetland
ecosystems in Florida were directly converted to other land
uses. The score card for the last year (1987), as a result of
Florida's aggressive legislation and rule making, is quite
Source: Florida Department of Environmental Regulation,
1987. With Proper education and continued attention given
to the importance of wetland ecosystems, the successes of
Florida can easily be duplicated in other States and regions
throughout the United States.
However, the protection of wetlands is not simply a
matter of eliminating direct conversion to other land uses.
The question of wetland loss has become one of degree and
1 Research Scientist, Center for Wetlands, University of Florida,
Phelps Laboratory, Gainesville, FL.
timing and no longer one of direct conversion. Increasingly,
we have begun to witness the continued deterioration of the
quality of wetlands that have been "saved" from conversion
and have been incorporated into the urban fabric of rapid
growth areas of Florida. Our recent experiences suggest that
loss of wetland function and "slow" conversion through
changes in surface water and groundwater hydrology and
regional nutrient dynamics may be having as severe a
consequence as simple direct conversion, only much less
noticeable. The implications are serious. The quality of
wetlands in rapidly urbanizing landscapes has been greatly
compromised and while they still exist after the wave of
development has passed them by, their very existence in the
long run is questionable.
In this paper the impacts and consequences of urbanization
on wetlands are explored, and several long term solutions
to the serious implications of recent trends observed and
measured throughout rapidly urbanizing areas of Florida
CUMULATIVE IMPACTS OF URBANIZATION
Wetland Community Types
The impacts of development on wetland ecosystems have
different consequences and magnitudes depending on the
type of community, its position in the landscape, and the
development action. Illustrated in Figure 1 are various
wetland community types arranged according to nutrient
regime and hydroperiod. Since wetlands represent a point
of convergence in the landscape, the size of the watershed
governs the amount of water and nutrients that are
concentrated within the wetland.
Bayheads and bogs, with little or no watershed rely almost
exclusively on inputs of rain water or, in some cases,
groundwater seepage. Cypress ponds and flatwood marshes
have some drainage from the surrounding landscape with
increased nutrient concentrations and hydroperiods. Where
watershed area is equal to or slightly greater than the area
of the wetland, still larger nutrient concentrations and longer
hydroperiods are characteristic. Sloughs or strands develop
in low relief landscapes where surface waters from a larger
NUTRIENT ACCESS MAP VIEWS
HIGH WATER FLOW
Figure 1.-Landscape position related to nutrient access and water flows. Wetlands
are arranged according to nutrients and water from lowest (top) to highest (bottom).
In effect, the ranking also suggest sensitivity to modifications to nutrient and
hydrological regimes, where most sensitive wetlands are at the top of the diagram.
(from Odum 1984)
watershed converge in broad sluggish flows in ill-defined
channels. River floodplain forests result where watershed
areas are quite large and where highest water flows and
nutrient access are characteristic.
Productivity and structural properties of wetlands are
related to nutrient loads and hydroperiods. Bogs and
bayheads, at the low end of the spectrum, tend to have low
species diversity and lower overall biomass, while river
floodplain forests have much greater biomass and diversity
of species. Thus landscape position, in general, directs
availability of nutrients and water and, more or less, the type
of wetland community that may develop. Certainly other
factors like frequency of drought and fire have an organizing
influence and may alter community type and species
Figure 1 can also be thought of as a diagram of wetland
sensitivity. Wetlands near the top of the figure have driving
energies of lower magnitude and flux than those toward the
bottom and are more apt to show signs of community
reorganization under a given impact. Low nutrient wetlands
with relatively small hydrologic variation are easily
disrupted with minor alteration in hydrologic regimes in the
surrounding landscape. Whereas minor modification of
hydroperiod and depths of inundation of floodplain wetlands
usually has relatively inconsequential effect on community
Table 1 lists wetland community types found in central
Florida and several of their most important characteristics.
The communities span a wide range of environmental
conditions; probably the single most important of which are
'. .' e . ''
. . ., .... ..
.' *. *. '.
hydroperiod and depth of inundation. Water depths and the
duration of flooding within wetlands seems to have a greater
organizing influence on community structure than other
factors. Changes in hydrologic regime, then, can shift
community structure toward an assemblage of species that
are better adapted to the new conditions. In some regions
where introduced (exotic) species are prevalent, the new
hydrologic regime often increases the invasion of introduced
species that are better adapted to the new conditions.
In landscapes dominated by humanity, hydrologic regimes
are often altered to accommodate changes in land use. In low
lying areas and landscapes of low relief, drainage works are
often constructed to lower groundwater tables and as a
means of managing the increased volumes of storm water
that result from increased impervious surface. In higher
relief landscapes, storm water systems route increased
volumes of runoff to downstream areas increasing magnitude
and shortening duration of hydroperiods. These changes
usually are accompanied by changes in nutrient availability.
In all, urbanization changes hydrologic and nutrient regimes
in the local landscape; in some instances decreasing depths
and duration of flooding and nutrient availability and in
others, increasing water levels and nutrient concentrations.
Modification of the landscape to accommodate
development, while not directly infringing on wetland
communities, often has long term impacts as the hydrologic
regime shifts in response to the characteristics and
requirements of urban land uses. In recent studies of created
wetlands in central Florida (Brown et al. 1988), a series of
undisturbed wetlands were needed as controls. After
surveying wetlands within the study area, it was quite
obvious that disturbance increased with proximity to
urbanizing landscapes. The more urbanized the surrounding
area, the lower the "quality" of the reference wetland.
A Landscape Perspective of Wetland Succession
The classic view of wetland succession starts with open
water and proceeds through marshes, shrub swamps,
forested swamps, and finally mixed hardwood forests. While
this may seem to make intuitive sense, the actual process
may be quite different.
Table 1.-Characteristics of wetlands in north central Florida (from Brown and Starnes 1983)
Hydric hardwood Cypress Wet Shallow Deep
hammock swamp dome Bayhead prairie marsh marsh
Water quality enhance-
ment, % removal
Phosphorus 40 90 98 85 40 98 30
Nitrogen 40 98 92 85 60 97 30
(mm/day) 4.8 5.8 3.8 3.0 5.4 5.6 5.6
Hydroperiod (days) 100-150 200-250 250-300 200-250 150-200 365 365
High water (m) 0.10 0.60 0.50 0.30 0.50 0.70 1.00
Low water (m) 0 0 0 0 0 0 0.20
Maximum level (m) 0.30 1.50 1.50 1.00 1.50 2.00 2.00
(m3/m2/yr) 0.1 0.1 0.84 0.6 0.37 0.68 0.1
Peat depth (m) 0-0.2 0-0.5 0-0.5 0.5-0.3 0-1.5 0.5-3.0 0-1.0
Life form richness 3 4-5 4-5 4-5 2 3 3
Wildlife utilization 86 71 56 32 74 84 84
Gross primary produc-
tivity (g organic
season 60 52.1 25.3 20.0 23.9 19.6 54.5
Permanent Submerged &
Water F Floating Emerged
Habitats Aquatics Aquatics
..\ Peat Phase
S I \ and FIRE aoute
Water F loatIn Emrged a r-he. Hardwood -
Habitats Aquatics Aquattc Wet Prtreo Swapms
Swamps - -
Figure 2.-Diagram (top) showing primary stages in plant succession in north-central Florida suggested by Monk (1968).
The bottom diagram has additional pathways of succession toward the left resulting from drought oxidation of peat
accumulations and from fire.
Figure 2 illustrates two concepts of wetlands succession
in north central Florida. In the classical sense, wetland
succession is said to be driven by accumulation of organic
matter and a resulting slow change in depth and duration
of flooding. As organic matter accumulates, the volume of
water detention decreases and hydroperiod is shortened. All
other things being equal, these trends would suggest
environmental change that favors a shift in species
composition to species better adapted to drier conditions.
However, all other things are not equal. Imbedded in a
dynamic landscape driven by cyclic pulses of drought and
flood and occasional fire, wetlands have little chance of
attaining textbook succession. In the real landscape where
drought increases oxidation and the potential for fire,
accumulation of organic matter to levels that would push
successional trends toward drier conditions is the exception.
Most probably, in the long run, accumulation of organic
matter is balanced with oxidation as wetlands dry out from
time to time and fire occasionally burns hot enough to kill
vegetation and lower ground surface elevations in its wake.
The landscape then, is a dynamic system of driving
energies and interrelated components that produces an ever
changing mosaic of ecosystems in a continuum of successional
stages. Add to this mosaic, human influences, and the net
result is still further complexity, fragmentation, and
increased cycling between successional stages.
An important consequence of fragmentation and increased
urbanization of surrounding lands has been to shift wetland
successional patterns. Drier conditions brought on by
lowered water tables and the berming effects of roadways
coupled with changes in frequency of fire occurrence, have
sped up wetland succession in some cases and in others
caused the system to revert to earlier successional stages.
The exact consequences depends on type of wetland and
combination of exogenous impacts. Where groundwaters have
been lowered and the wetland protected from burning,
succession tends toward the right in Figure 2. If the wetland
burns, because of the drier conditions, often the fire burns
deep through underlying peat, and succession is toward the
left; how far left is controlled by the depth of the burn.
Impoundments are less common than drainage, but where
waters are impounded within a forested wetland, open
water and emergent wetlands are created as the deeper
water kills most trees, thus succession is toward the left.
The process of urbanization and agricultural conversion of
lands seems to speed up the time constants of the landscape.
Clear cutting seems to mimic disastrous fire in its ability to
reverse forest succession. General drainage of the landscape
seems to push wetland succession toward drier conditions.
Fragmentation resulting from sprawling urbanization quickly
produces island refuges of wildlife and vegetation. The
mosaic of ecological communities, agricultural lands and urban
places becomes increasingly fine grained with increased
human use. Figure 3 illustrates this point showing changing
community structure and landscape organization with
increased fragmentation in a portion of central Florida over
a time frame of about 40 years. What was once a landscape
of sandhills dominated by a large heterogeneous wetland of
cypress and marshes, has become over the years a
fragmented landscape of shrub swamps and remnant swamp
forests dominated by human uses. The imports shown here
are less the result of direct conversion than they are of
secondary impacts of ditching, draining, and roadway
construction. The general pattern throughout developing
landscapes is first alteration of environmental conditions
through fragmentation and drainage, and then development
for urban uses later when wetlands are less viable or
IMPLICATIONS FOR MANAGING THE
The environmental conditions of the urbanizing landscape
are quite different from those of the nonurbanized landscape.
The processes of urbanization converts wildlands to urban
uses leaving behind pockets of forested lands, old
agricultural fields, and wetlands. Drainage works and
impervious surfaces alter hydrologic regimes and in turn
affect downstream and isolated wetlands. Left untouched,
these remnant islands of the former landscape reorganize in
response to the new conditions. The extent of reorganization
depends on the magnitude of the impacts and the size of the
remnant island. Larger islands have greater bufferingg"
capacity while small isolated systems tend to exhibit less
resiliency. Managing the urbanizing landscape to insure the
continued productivity and biological functions of forested
patches (whether wetland or upland) may be an impossible
task if the goal is to maintain these systems in some static
unchanging state. Successional changes brought on by
changing environmental conditions may force today's wetland
toward tomorrow's upland. The loss of wetland function in
itself may not be of critical concern, especially in heavily
Figure 3.-Map showing the effects of development in and around an extensive wetland system near Orlando, Florida. Aerial
photographs were taken from Palmer and Tighe (1988), interpretation and compilation for 1946 and 1981 by the author, wetland
interpretation in 1988 by Palmer and Tighe.
Figure 4.-Time series sequence of succession in urban drainage ditches if vegetation
is allowed to colonize. Vegetation acts to retard flow through friction, yet during
storm events the system can still function effectively. Once canopy is established,
herbaceous vegetation is shaded out and the stream channel resembles a first order
urbanized areas, if it were not for the fact that a good bit
of our regulatory effort now-a-days is concerned with sparing
these systems from conversion.
The general trend throughout Florida in the past several
decades has been a progressive drying out of the landscape
and a consequent shift in wetland ecosystems toward drier
and drier community types. While wetlands have generally
been "spared" from conversion to other uses, they have not
been left unchanged. The cumulative effects of a changing
landscape have slowly but surely caused serious erosion in
the quality and quantity of wetlands within and adjacent to
rapidly urbanizing regions of the state. Public policy has long
recognized the value of wetlands, and has been successful
in minimizing their conversion to urban uses; however, their
continued decline in quality as a result of overdrainage is
little recognized. Might it be better policy to discourage
overdrainage and seek ways of rehydratingg" the landscape?
To more effectively manage the landscape in the face of
increasing development pressure it is imperative that the
cumulative, secondary impacts of urbanization be given
considerable attention and regulatory initiatives be directed
at reversing current trends. To this end, the following
management guidelines for urbanizing landscapes are given
as a means of establishing a regulatory framework.
Educate the Public
As in most environmental programs, a sound approach to
educating the public is extremely important. Public
perception has long been that swamps are ok if seen on TV,
but not in the backyard. Couple this with the perception
that wetlands produce mosquitos and mosquitos carry disease
and it is relatively impossible to convince the general public
that wetlands are an important part of the urban fabric.
Programs need be developed that increase public awareness
of the importance of wetlands within the urban fabric.
A second area needing increased public awareness is
especially important. The public has come to expect that
their cities and neighborhoods will remain dry during any
and all rainfall events. Storm waters are expected to drain
quickly after any event, and if they do not it is cause for
great displeasure. The public must be made aware of the
benefits of a wet landscape, and learn to accept some
standing water during the wetter times of the year.
The lowering of groundwater tables to accommodate
housing and roads has a wider influence than just the
developed portion of the landscape. A better method of
development is to elevate housing and roads and expect some
flooding during extreme rainfall events. Encourage the use
of vegetated and forested drainage structures (Figure 4) that
act to impede surface water discharge, but allow for storm
waters to discharge through meandering channels that mimic
natural first order streams.
Rehydrate the Landscape
Where overdrainage has occurred, it may be possible to
reverse these trends by recycling treated wastewaters back
on the land instead of depositing them in surface water
bodies, the ocean, or deep well injection. By encouraging
landscape recycle through natural wetlands, constructed
wetlands, overland flow systems, and spray irrigation
systems, area groundwater tables are replenished.
Encourage the use of vegetated wetland retention systems
for storm water management. Instead of grassed detention
basins that require continual maintenance, wetland retention
basins (Figure 5) require no maintenance, add to landscape
diversity, increase wildlife habitat values, and act to hold
and conserve storm waters on site replenishing local
Manage Resources at the Landscape Scale
Increasingly, it has become obvious that a piecemeal
approach to landscape management can only lead to an ever
increasing fragmentation of the landscape. This revelation
has recently lead the author to propose a concept for
landscape management that incorporates the best of physical
land use planning related to growth management and
landscape ecology, as well as results of research related to
the Florida landscape that suggest a continuing trend of
environmental deterioration. The concept has been termed
"Wildlands Management" and has as its fundamental
objective the identification and preservation of a landscape
mosaic of wildlands that are large enough to provide
Figure 5.-An illustration of the potential of wetland stormwater
retention systems. In the top diagram the retention basin is
clogged with herbaceous vegetation and requires continuous
maintenance, while if allowed and encouraged to develop forested
canopy would be more self-maintaining.
significant wildlife habitat, are capable of suffering
development impacts from adjacent lands, can contain urban
sprawl and give definition to urban areas, and are
ecologically diverse and relatively intact.
The motivation for Wildlands Management has developed
as a result of observations of the rapid urbanization of the
Florida landscape. As regions experience urbanization,
small pieces of the landscape are left undeveloped either
because they are "protected" or because they have been
purchased for their potentials as preserves. These fragments
become islands in a sea of developed land. Often resented
by their neighbors, because they contain unwanted vestiges
of the former landscape, these patches suffer from either
neglect or overexposure. Most often they slowly deteriorate
to the point that one must question if they could survive
without massive doses of human management.
As long as there is development pressure, urban areas
will continue to sprawl ever outward in wider and wider
circles of urbanization, leaving in their wake remnants of
the former wild landscape mosaic. Soon, if urbanization is
complete urban centers begin to merge and the landscape
becomes one dominated by developed lands with a smattering
of "protected" wetlands, parks, and wildlife management
areas. Not only do urban centers spread, but intensity of
uses increase as urbanization continues. The greater the
intensity, the less likely a remnant forested island can be
maintained without significant human management.
Presumably, without a wider perspective, that is, without
a landscape perspective, effective landscape planning and
management that might preserve portions of the landscape
mosaic as wildlands is not possible. The first stage in
developing a landscape perspective is to identify mosaics of
ecological communities that are relatively intact and that
might serve as the beginnings of a statewide wildlands
The initial premise upon which wildlands management
was based was grounded in the belief that a landscape
perspective is absolutely necessary to achieve meaningful
regulation and management of our natural resources. Past
efforts to develop a landscape perspective in the face of a
rapidly growing population and all its attendant
infrastructural requirements have been continually frustrated
by the lack of a macroscopicc," systematic approach.
Resources and authority over them are compartmentalized to
such a degree that it is impossible to manage the landscape
and regulate its use. We manage and regulate the parts. It
has long been known that the sum is greater than the parts,
yet our approach to achieving some measure of control over
the perceived impacts of human use of the landscape is to
delegate the management of water to one agency, air to
another, soil to another, wildlife to another, minerals to
another, and planning of the whole thing to yet another. The
wildlands management approach is an attempt to thwart
these impediments to a landscape perspective and achieve
consensus between the public and all agencies that the
landscape must be planned and managed as a mosaic of
contiguous blocks of developed lands and wildlands and not
a continuous sprawl of development having remnant patches
of recreational amenities. The approach can work if all
regulatory agencies, developmental agencies, and the public
work in tandem to develop a regulatory environment that
recognizes its absolute necessity and implements a wide
diversity of mechanisms to achieve it. Every mechanism of
"growth management" must be utilized. Transfer of
development rights, purchase of development rights, overlay
zoning, green belts, transfer of mitigation requirements,
impact fees, and performance zoning to name a few, can be
used to implement the wildland program. There are other
mechanisms, we are only limited by a lack of commitment.
Brown, M.T., G.R. Best, R.E. Tighe, and S. Roguski. 1988.
A Florida Pilot Study for Evaluation of Created and
Restored Wetlands. Final Technical Report to U.S. EPA.
Gainesville, FL: Center for Wetlands, University of
Florida (In Press.)
Brown, M.T., E.M. Starnes, C. Diamond, B. Dunn, P.
McKay, M. Noonan, S. Schreiber, J. Sendzimir, S.
Thompson, and B. Tighe. 1983. A Wetlands Study of
Seminole County: Identification, Evaluation, and
Preparation of Development Standards and Guidelines.
Final Report to Seminole County. Gainesville, FL:
Center for Wetlands, University of Florida, pp. 284.
Florida Department of Environmental Regulation. 1987.
Report to the Legislature, October 1, 1986 thru
September 30, 1987. FDER, Tallahassee, FL.
Monk, C.D. 1968. Successional and Environmental
Relationships of the Forest Vegetation of North Central
Florida. The American Midland Naturalist 79(2).
Odum, H.T. 1984. "Summary: Cypress Swamps and Their
Regional Role." Pages 416-44. In: K. C. Ewel and H. T.
Odum (eds.). Cypress Swamps. Gainesville, FL:
University Presses of Florida.
Palmer, C.N., and R.E. Tighe. 1988. Wetland Inventory
and Rating System: Southwest Growth Management Area
Plan. Technical Report to the City of Orlando. Dyer,
Riddle, Mills and Precourt, Inc., Orlando, FL.
Reprinted from the Proceedings
Hook, Donal D.; Lea, Russ, eds.
1989. Proceedings of the symposium: The forested wetlands of the Southern
United States; 1988 July 12-14; Orlando, FL. Gen. Tech. Rep. SE-50.
Asheville, NC: U.S. Department of Agriculture, Forest Service,
Southeastern Forest Experiment Station. 168 pp.