Can I interest you in some Florida
by Richard Moyroud
Originally published in "The Palmetto",
the magazine of the Florida
Native Plant Society,
Volume 18, Number 2, Summer 1998
Images from University of Florida Center for Aquatic and
Click images to enlarge and links within the text for complete
information at CAIP
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This article is concerned primarily with freshwater wetlands
dominated by trees, and while most often referred to as "swamps,"
they are now identified by the more precise phrase "forested
wetlands." In any case, the type of plant community in question
is what most people would recognize as a "swamp" if
they walked into it, as their feet would likely get wet or sink
into soft soil. Such water-saturated soils are dominated by plants
which tolerate such extreme, although usually seasonal, conditions.
These ecosystems are a significant part of Florida's natural
landscape, and hold plants which have developed fascinating strategies
for coping with adverse conditions. Wetlands have also been central
to the human history of Florida, and humans, with conflicting
short-term goals, are now determining the future of what remains
of these productive, beautiful systems.
Larger image | CAIP Swamp Scenics
The humorous title chosen is meant to remind us of earlier years
when Florida wetlands were peddled to uninformed buyers, who
then found themselves with valueless property; the true "value"
of such land may best be measured in a realm which is outside
of commerce and short-term return on dollars invested. The curious
term "reclamation" was often used when wetlands were
drained for human occupation; this implies that they once did
belong to us, and were somehow taken (by whom?), thereby justifying
our reclaiming them as rightful property. We will someday deeply
regret the arrogance, lack of foresight, and simple greed which
has dominated wetland policy and actions over the last few generations,
and is apparently continuing with current landholders and decision
Although arbitrary surveyors' lines signal political boundaries
between most states, much of the current Florida landmass is
defined by a natural boundary, where the land meets the Atlantic
Ocean or Gulf of Mexico. In calmer tidal areas, these boundaries
are diffuse, and mangroves or salt marsh plants dominate, forming
forests in the south and fields to the north; in high energy
areas, the shoreline is clearly defined by loose sand mounded
into dunes, either bare and shifting or colonized by plants adapted
to fluctuating degrees of salt, sandblasting, and drought. Within
the boundaries delimited by maritime ecosystems (a topic for
another article), there are large areas of land where rain or
river water collects, or where freshwater seeps to the surface.
When water is standing on the surface for more than 10% of the
growing season, the site then meets the technical definition
of "palustrine" (from the Latin for "swamp.")
Of all the popular terms for wetlands, the word "swamp"
probably has the largest number of connotations, most of them
negative. In fact, the various common names used for such areas
have caused great confusion, and eventually had to be addressed
when wetland protection legislation was passed and promptly challenged.
Today, wetland delineation is based on defensible observations
of soil types, plant communities, and hydroperiod, all carefully
outlined in technical manuals and established in the field by
Palustrine systems include a wide range of wetland plant communities,
most of which we would call swamps, but better denoted by technical
terms, such as hydric hammock, wet prairie, the Everglades "swale"
or marsh, and many others. Note that "marsh" is used
for sites dominated by herbaceous plants, and with few or no
trees. The Florida
Natural Areas Inventory lists at least twelve distinct plant
communities of forested wetlands in Florida, each with synonyms
under other authors' classifications. These ecological definitions
are generally descriptive, reflecting substrate, water source
(basin depressions, floodplains, or seepage), dominant plant
species, and natural maintenance cycles, such as fire. As might
be expected, baldcypress (Taxodium distichum), pondcypress (Taxodium
ascendens), and tupelo (Nyssa spp.) are frequent components of
our forested wetlands. These particular species exhibit many
special adaptations, but are also magnificent trees with fascinating
Human history has always been linked with wetlands, partly because
of our need for freshwater, but also because wetlands can be
very productive ecosystems. From our point of view, there is
a down side to this biological productiveness, since it includes
organisms that can be harmful to humans, from microscopic disease
organisms to larger predators, all lurking in the shallows. The
popular picture of a primeval swamp, rife with enormous snakes,
alligators, leeches, mosquitoes, and malaria is unfortunately
the dominant idea for most, and has been reinforced by elaborate
artwork from the 19th century, usually depicting intrepid British
explorers fending off imaginary creatures rising out of a great
steaming swamp jungle.
Once again, part of this image has a basis in fact, because
swamp trees show unusual adaptations to flooded soils. Stilt
roots, prop roots, and aerial roots, draping down from overhead
branches, all appear as sinister tentacles attempting to capture
and consume the innocent wanderer. On flooded soils, roots grow
upward like stalagmites, form loops, or send many small breathing
roots up from the mud, perhaps looking like fingers of chthonic
beings and adding to the lugubrious mood of the forest. Large
flaring buttresses at the base of tree trunks add to the strange
architecture, and unstable soils (including the cliché
quicksand) all contribute to giving these forests a reputation
for danger and evil. Even the name "malaria" is a contraction
of the Italian "mala aria" meaning "bad air,"
since the disease was blamed on "vapors" rising from
the swamps. Yet these same sites attract philosophers and scientists,
and may reveal to us a glimpse of the world as it was before
domination by human presence and its overwhelming artifacts.
There are several underlying reasons for the unusual architecture
of plants in swamps, including physiology and mechanical or physical
limitations. Green plants require a balance of basic resources
for successful growth: sunlight, liquid water, gaseous oxygen
and carbon dioxide, and minerals. In the real world, the perfect
combination of these factors is rare, except perhaps in tropical
rainforests. Deserts present obvious shortcomings in the limited
amount of available water; polar regions resemble deserts in
limited water, because if present it is almost always frozen,
but light is also severely reduced in the winter. Wetlands would
seem to be the ideal environment, with abundant freshwater, sunlight,
minerals, and atmospheric gasses, but vascular plant roots require
considerable gas exchange. Simple physics limits the movement
of gas into deeper water (think of a snorkel several feet long,
and how difficult it would be to breathe, fighting against water
pressure.) Microorganisms and chemical reactions further consume
oxygen, and toxic elements or compounds accumulate in the substrate.
As a result, most woody plants are not tolerant of flooded soils,
and those which grow in flooded sites have evolved beautiful
strategies for survival.
In the most extreme cases, swamp plants must germinate and
grow underwater. In fact, very few wetland trees do so, some
because their fruits are buoyant (for dispersal) or growth may
be inhibited until gas exchange improves. When conditions are
right, they must germinate quickly on exposed muddy soil (an
event which might occur only a few times per decade, indicating
the benefits of occasional drought), establish a firm root system
to prevent being washed away, grow in height as much as possible,
then prepare to live like an aquatic plant, spending half the
year under water. In Florida, most wetland tree and shrub seedlings
might have to endure these conditions for just a few years; in
the Amazon Basin, where water levels rise 40 feet every season,
mature trees and palms that offer a shady canopy in the dry season
become aquatic plants in the wet season, with their entire crowns
submerged like coral reefs. This is an extreme example of adaptation
to flooding, and the methods by which these plants survive is
still under investigation. Certainly, water quality and other
factors in the habitat play a role, but the overall picture of
the flooded forest is very intriguing.
Plants are the most efficient devices on earth which collect
and store solar energy. The chemical process which is used to
release this energy depends on the availability of oxygen. In
the absence of oxygen, the chemical cycle leads to the production
of ethanol (pure alcohol), which at higher concentrations is
lethal to living organisms. Some research has suggested that
wetland plants use a modified metabolic pathway when oxygen is
lacking, leading to different, non-lethal, end products (such
as malate, a salt or ester of malic acid), but these results
are not universally accepted. Improved aeration, as allowed by
structural changes described below, may help in limiting the
amount of anaerobic respiration and its toxic by-products. In
temperate zones, flooding during the winter season causes less
harm because plants are dormant, and the biochemical cycles are
slowed dramatically. This kind of suspended animation may also
occur in tropical species, especially when light levels are reduced,
as happens in deep water.
A third strategy occurs in some wetland species, where flooding
will cause the death of secondary roots, but the plants are apparently
capable of regenerating new roots when conditions allow, resulting
only in slower overall growth of the individual. In this vein,
it should be noted that many wetland trees will grow well on
higher ground, but are less able to compete with other upland
species. By evolving tolerance to conditions which would kill
most other plants, wetland trees thrive with reduced or absent
competition, sometimes forming large stands of only one or two
species. As a result, some wetlands may actually be less diverse
in species than adjacent uplands, but the ecotone (or transition
between the two) is always rich in species and is especially
valuable for foraging and hunting animals.
Structural adaptations to wet soils are easier to observe and
interpret. Roots, stems, leaves, and fruits all show some adaptation
to flooding. Again, oxygen is the driving factor, so while most
roots are positively geotropic (moving toward the earth), many
wetland roots grow in the opposite direction, and are often called
"breathing roots," but can also be assigned technical
terms such as pneumorhizae, pneumatophores, or pneumathodes.
The most dramatic and common example is that of cypress "knees,"
a part of the root system which forms conical of rounded projections,
from a few inches to twelve feet in height. The production of
knees seems to be most abundant on sites which are alternately
wet and dry, and the height of the knees is commonly thought
to reflect the highest water level. Many experiments have been
done to establish the function of these knees, and although it
seems logical that they should help in obtaining gasses, the
proof is not absolute. One convenient but sad misconception was
expressed by a harvester of cypress trees for shredding into
mulch; he stated that cypress knees are actually young cypress
trees, ready to grow up as replacements after the adults are
cut and dragged out of natural swamps!
In coastal Florida, the most commonly seen pneumatophores are
the peg roots of black mangrove (Avicennia germinans), about the size
of a pencil, often carpeting the ground as very dense mats. However,
similar structures are produced by many palms, and by certain
hardwood trees under specific conditions; tulip poplar (Liriodendron
tulipifera) occurs throughout the eastern deciduous forest
in upland situations. In the coastal plain, as far south as
Orlando, it is found growing on hummocks in swamps, where although
rarely inundated, the soil saturation is enough to cause the
formation of small vertical peg roots. Swamp tupelo (Nyssa sylvatica var. biflora)
and water tupelo (Nyssa aquatica) produce roots which
form loops above the soil surface, sometimes wrapping around
cypress knees. It has been argued that these structures help
trap debris, and thus build up a mound of soil at the base of
the mature tree, helping it to enlarge its own hummock of aerated
soil, free from competition. Stilt roots, prop roots, and other
aerial roots grow out from the trunks or branches of trees, eventually
connecting with the soil below, creating a strong physical support
as well as a pipeline for water and nutrients. Red mangrove (Rhizophora
mangle) in coastal areas shows the best developed stilt
roots, and strangler fig (Ficus aurea) usually shows some aerial
root development, and prop roots when growing in flooded soils,
almost as if to keep the trunk out of the water. Actually, strangler
fig seems to prefer better drainage, and often occurs as an epiphyte,
but if a seed germinates and grows on a log or tree stump, the
roots will persist and enlarge, long after the stump has decomposed.
Cypress and tupelo often show basal swelling in the trunk, a
feature that recurs in many species of wetland trees. It has
been argued that this gives trees more stability in unstable
soils, especially when large plank buttresses radiate from the
trunk. While most evident in tropical trees, such as our native
strangler fig, both cypress and Florida elm (Ulmus floridana)
develop respectable buttresses on wet soils. Bell or bottle-type
swelling of the base of the trunk is found in cypress, swamp
tupelo, water tupelo, pond apple (Annona glabra), pop
caroliniana), and even red maple (Acer rubrum), but attains truly exaggerated
proportions in cypress trees in north Florida.
Another explanation for basal swelling (also called stem hypertrophy)
is suggested by the internal wood anatomy: large, low density
cells dominate and may allow better gas exchange. The low density
wood is easy to identify when dry, because it is almost as light
as balsa; the wood of many swamp trees has in fact been used
to make floats for fishing nets. A more pronounced internal change,
often visible in cross-sections of plant roots and stems, is
the occurrence of large gas-filled cavities in cortical tissue
arranged around the central xylem. These canals, known as aerenchyma
tissue, act as pipes to carry greater volumes of gasses more
efficiently. In this way, wetland plants have evolved an internal
architecture which allows normal biochemical processes to continue
despite the limiting factors and stresses imposed by the environment.
While the search for increased aeration is easy to understand,
some anatomical features of swamp plants seem contradictory.
This is seen in the leaves of many wetland plants, which show
a strong similarity to those of very dry areas. Sclerophylly,
the production of small, hard textured, glossy leaves is common,
contrary to what might be expected where water would not seem
limiting. In fact, seasonal dry periods, high levels of sunlight,
wind, high rainfall, and inundation all have a damaging effect
on leaf tissue. Some swamps are limited in available nutrients,
and plants can conserve energy by producing small, durable leaves,
especially when abundant light is available. These leaves have
thick cuticles and are often coated with wax, as much to keep
water out (which would leach nutrients) during floods and rains,
as to keep water in during droughts.
Other anatomical changes can be more ephemeral and are produced
only during periods of inundation. Lenticels are small pores
on the surface of plant stems and roots, and often appear as
raised dots or lines on the bark of woody plants. Normal lenticels
are essential for the entry of oxygen, but are often hypertrophied
(abnormally large) when plants are flooded, indicating a more
active function, and again helping to provide the gas exchange
needed for growth. Lenticels can often be seen on pneumatophores.
Adventitious roots are those roots produced directly from a stem
above ground, and their presence is a common response to seasonal
flooding. These roots again help with gas exchange, but also
absorb any available dissolved nutrients. In cases where flooding
deposits silt, these roots then grow into the new level of soil,
and may continue to do so annually, leaving the original grade
and base of the tree far below the surface. Actually, flood-borne
silt deposits along rivers have created some of the most fertile
soils in the world, and allowed the greatest advances in early
agriculture. Ironically, the same floods today are reported as
disasters, and every effort is made to prevent any recurrence,
especially when houses are built at grade in well-known floodplains.
Among wetland trees, baldcypress and pondcypress are especially
interesting and reveal a fascinating history. Although true conifers,
which are generally thought of as evergreen cone-bearing trees
of dry, cold latitudes, swamp cypresses (which do bear cones),
grow in flooded southeastern sites and are deciduous. Among wetland
trees, they are among the most tolerant of flooding, surviving
even when swamps are impounded and water levels remain constantly
high. It has often seemed odd that this conifer should be deciduous
in the south, where cold winters are not a limiting factor as
they are closer to the poles, where many trees endure the winter
in leafless dormancy. A possible explanation comes from plant
fossils found in Alaska, and the picture they indicate is that
of a plant community resembling modern-day cypress swamps, complete
with a diverse fern understory. It is generally accepted that
cycles of warmer polar temperatures did allow abundant plant
growth at higher latitudes, but daylength would still resemble
the cycles we see today, so for six months of the year, solar
radiation would be severely limited. In light of this observation,
the loss of leaves, even in warm temperature regimes, suddenly
makes sense since leaves without sunlight are more of a liability,
exposed to rain, wind, and hungry dinosaur herbivores. Today,
the retained deciduous habit may be as beneficial in southern
swamps with winter droughts, even though winter darkness is no
longer a limiting factor.
Since forested wetlands offer a third, aerial dimension, to the
ecosystem, there are organisms which thrive in swamp forests
even though they cannot tolerate flooding. This added dimension
is the surface area available on trunks, branches, and leaves
of woody plants. As in the tropical rainforest, there is competition
for sunlit sites with reasonable access to nutrients and water;
these same sites are out of reach of many herbivores.
Orchids, bromeliads, and ferns are the vascular plants which
dominate our available swamp scaffolding, but closer inspection
will reveal lichens, mosses, and liverworts on bark, usually
showing a very distinct zonation based on the high water mark. This
permanent characteristic chronicles the history of seasonal flooding
and is reliable enough to be used as a part of wetland delineation.
Algae and fungi will occur throughout wetland forests, and
along with liverworts, can be found as epiphylls, growing on
the surface of leaves, much as they do in the humid tropics.
Vines often thrive in swamp systems, adding their own complexity
to the forest; they create aerial walkways above the water, allowing
animals to move throughout the canopy. While making foot travel
more difficult, it is unlikely that vines in swamps are any more
damaging to trees than they are in any other natural system.
Whether seen as obstacles to overland travel, as reservoirs
of pestilence, or as oases of life, swamps provide habitat to
a vast array of animals we prize, particularly bird life. The
last panthers in Florida exist in part because of our own difficulties
in navigating or eliminating swamps. Cypress trees hundreds or
thousands of years old, akin to the redwoods of the west, have
mostly been felled for timber, although a few living examples
remain to inspire awe in those who are susceptible. The Fakahatchee
Strand, perhaps the richest forested wetland in North America,
is mostly in public ownership, but has many difficult management
issues to address, as do most natural areas finally acquired
and set aside. A long-term view of responsible land management
may only begin when we develop an appreciation for the inherent
values of biological diversity. Despite our preconceived ideas
and learned fears, the swamp is probably a very good place to
start, or at least a good place to get wet.
Brown, Clair A., and Glen N. Montz. 1986.
Baldcypress: The Tree Unique, The Wood Eternal. Claitor's Publishing
Division, Baton Rouge, Louisiana.
Dennis, John V. 1988. The Great Cypress Swamps.
Louisiana State University Press, Baton Rouge.
Ewel, Katherine C., and Howard T. Odum, eds.
1984. Cypress Swamps. University of Florida Press, Gainesville.
Eyre, F.H. editor. 1980. Forest Cover Types
of the United States and Canada. Society of American Foresters,
Florida Natural Areas Inventory (FNAI). 1990.
Guide to the Natural Communities of Florida. FNAI and FDNR,
Gilbert, Katherine M., et al. 1995. The Florida
Wetlands Delineation Manual. Florida Department of Environmental
Goulding, Michael. 1990. Amazon: The Flooded
Forest. Sterling Publishing Co., New York.
Kozlowski, T.T., ed. 1984. Flooding and Plant
Growth. Academic Press, New York.
Lugo, Ariel, Mark Brinson, and Sandra Brown.
1990. Forested Wetlands. Elsevier, New York.
Myers, Ronald L., and John J. Ewel. Ecosystems
of Florida. University of Central Florida Press, Orlando.
Vileisis, Ann. 1997. Discovering the Unknown
Landscape: A History of America's Wetlands. Island Press, Washington,