How the Swamp Formed
is a huge depression, shaped like a gentle saucer tilting south. Higher
land lies to the north (the Bacon Terraces), the west (the Tifton Upland)
and the East (Trail Ridge). Trail Ridge is probably a former barrier
island built roughly one million years ago, when the sea level was about
40 miles further inland than it is today. The Okefenokee depression
was a marshy lagoon behind the ridge. Over the millennia, the sea retreated.
The clays of the old lagoon translocated through sands below them, helping
to seal the bottom of the swamp. Water was unable to flow east, blocked
by Trail Ridge, so the Suwanee River drained to the Gulf. (Eventually
the St. Mary's River breached the ridge, allowing some of the Okefenokee's
water to reach the Atlantic.)
For a time, the
Okefenokee was not a swamp: it was probably a pine and oak forest with
scattered wetlands and freshwater streams. Water tables rose, however,
and large areas became flooded. Peat began to build about five to seven
thousand years ago, forming the Okefenokee Swamp as we know it today.
years ago, Trail Ridge was a barrier island, like those of the Georgia
Coast today. The Okefenokee was a marshy lagoon behind it. Photo
by Hugh and Carol Nourse.
Building a Prairie
The prairies of the Okefenokee
are fascinating, constantly changing communities. Aquatic plants, seas of
grasses and islands float among expanses of water, creating a vast and serene
wilderness. Peat, water, plants and fire work together to create this unique
Peat is made
up of partially decomposed plant material. It forms when there is
not enough oxygen available for bacteria to break down dead vegetation.
The lack of oxygen occurs because the gently tilted saucer beneath
the swamp, with its clay seal and some impermeable rock beneath,
holds in the water, which moves very slowly in the swamp. (This
is especially true on the east side; Suwanee River currents move
water faster on the west side of the swamp.) The oxygen in the slow
moving water is quickly used up, and without oxygen, bacteria must
break down organic material using slower, less efficient anaerobic
(oxygen-free) processes. Swamp gas (methane) is a by-product.
These slow decay processes fail to break down all the plant material,
so the peat builds.
Contrary to what
many believe, the Okefenokee is not a sphagnum moss bog. Peat cores
from the swamp bottom show that the peat is mostly made up of the remains
of the most common plants here, such as water lilies (Nymphaea odorata),
Virginia chain fern (Woodwardia virginica), and pond cypress
(Taxodium ascendens). Sphagnum mosses, which are the major
ingredients of many northern bogs, are present in the Okefenokee, but
they don't play such a large role here.
water lily (Nymphaea odorata). Lower, Virginia chain fern (Woodwardia
virginica) under cypress. These are some of the main peat forming plants
of the swamp. Photos by Cheryl Brown.
peat is very acidic (the pH is roughly 3.5, with 7 being neutral). Humic
acids and tannic acids seep from the soils of the nearby pine-oak uplands
and from the decomposing peat. Sphagnum moss adds to the acidic conditions
by acting like a "hydrogen pump", releasing hydrogen ions
(which make the water acidic) while taking in and locking up other nutrients.
graced by the splayed out parrot-beak shaped pitchers of a parrot pitcher
plant (Sarracenia psitticina). Photo by Fred Mileshko.
Land in the Okefenokee
rises and falls with the water level. Water level averages about two
feet. Rain is the main source of water in the swamp. Since rainfall
varies, huge changes in water level can take place from season to season
and from year to year. The highest rain levels occur in the summer,
but are offset by the draw down from evapotranspiration (evaporation
combined with the uptake and expiration of water by plants). Long
summer droughts can expose huge expanses of peat to the sun, making
it powder dry. Severe droughts occur about every 25 years.
(Orontium aquaticum). Photo by Hugh and Carol Nourse.
A charred cypress
tree, survivor of a surface fire. Photo by Richard Bryant from the book
The Okefenokee Swamp.
is a prime fuel for fire. (In fact, peat was mined from the east side
of the Okefenokee in the early 1900's as a fuel source.) Fire shapes
a number of environments in Georgia, but it plays a particularly fascinating
role in the Okefenokee. Here, fire not only burns the vegetation and
changes the plant communities: at times, fire reshapes the land itself
by searing through the peat. When peat is slightly moist, lightening
strikes may cause surface fires that only kill the above ground parts
of plants. But during droughts, the peat dries to deeper levels, and
rapacious underground fires may burn for weeks, killing plants entirely
and carving out new depressions. Such topography-changing fires apparently
occur about every 100 to 150 years.
Building Land: Vegetation
Succession in the Prairies
a huge fire creates a depression, rainfall fills the carved-out peat to form
a lake. These lakes are not permanent. They can return to land in at least
three ways. First, peat may pop to the surface, creating islands to be colonized.
Second, peat may build up or water levels may lower to expose new land. Third,
pond cypress trees may create ever-growing tussocks as their roots and knees
gather debris. These three processes are described below.
Rose pogonia (Pogonia
ophioglossoides). Photo by Fred Mileshko.
1. Blow-ups, Batteries
and Houses ( Building Land from the Top Down.)
blow-ups occur throughout the watery expanses
of the prairies. A blow-up is a piece of peat that has been dislodged
from the bottom of the swamp to float freely around the lake. Blow-ups
appear when alligators and snapping turtles stir up the swamp floor
and when pockets of methane gas lift pieces of peat to the surface,
like air balloons.
The blow-up is
not barren for long. The wind-carried seeds of broomsedge (Andropogon
glomeratus), sedges (Carex spp.), some forbs, and beak
rushes (Rhynchospora spp.) soon colonize the blow-ups, making
tiny rafts of vegetation that float by your canoe. Once vegetated, the
blow-ups are called batteries. Plant roots
stabilize the peat, and dead vegetation builds it up, enlarging the
rummaging through peat bottom of the swamp sometimes dislodge pieces
to cause blow-ups. Photo by Richard Bryant.
occidentalis), titi (Cyrilla racemeflora), dahoon holly
(Ilex cassine), pond cypress and loblolly bay (Gordonia lasianthus)
appear annd overtop the herbs. The large root systems of these shrubs
and trees solidify the battery. Pull your canoe to the island edges to
find pitcher plants (Sarracenia spp.), blue flag iris (Iris
virginica) and rose pogonia (Pogonia ophioglossoides).
float helter-skelter through the prairie, blocking boat trails, docking
at other islands, growing and stabilizing as the plant roots spread.
Eventually the roots anchor the mat to the peat floor of the prairie,
and pond cypresses grow tall enough to tower over the shrubs. The battery
is now called a house.
left, blue flag iris (Iris virginica). Photo by Rita Collins. On right,
progression from battery to house.
2. Building New Land
from the Bottom Up
and emergent plants quickly colonize a new lake, creating a stunning community
where lemon yellow and creamy white plants glow amidst the tea colored waters.
Golden-club, water lilies, cow-lily (Nuphar luteum), pickerelweed
(Pontederia cordata), and bladderworts gild the canoe trails that
weave through the prairies.
As these plants die and
decay, the peat builds. Once it builds to a height that exposes it to air,
or when drought lowers the water table to reveal the swamp's peat bottom,
the seeds of less hydric species, such as broomsedge, loblolly bay, swamp
loosestrife (Decodon verticillatus) and Virginia chain fern germinate.
As the prairie builds, hooded, yellow and parrot pitcher plants (Sarracenia
minor, S. flava, S. psittacina), sundews (Drosera spp.), butterworts
(Pinguicula spp.), pipewort (Eriocaulon compressum), blue
flag iris, sweet pepperbush, titi, button-bush, and Virginia sweetspire (Itea
3. Tussocks: Building
Land from Cypress Trees
cypress trees, too, can build land from a lake, one patch at a time. Their
seeds can't germinate in water: they germinate when water levels are low,
and expose the peat to air. The seedlings then grow very fast to outrace rising
waters. Over time, the trees grow large, with root systems and knees that
catch debris. These debris-strewn clumps are called tussocks, and are miniature
nurseries that plants colonize. Like a huge jigsaw puzzle the pieces sometimes
slowly grow together to form a whole.
Cypress knees and
roots trap debris in which plants root. These in turn collect more debris,
and land slowly forms. Photo by Cheryl Brown.
The Great Kaleidoscope
Okefenokee is a huge ecological kaleidoscope. A battery may sink, then rise
again. An exposed prairie patch may stay above water or drown. The arrival
of a particular species to a battery or house varies with the random vagaries
of wind, season and seed production, so no two islands are alike. Drought
dries out the land, killing some hydric plants, and letting mesophytic land
plants grow, then drowning kills the land plants and brings the hydric species
back again. Always, as the kaleidoscope turns, though, the progression from
water to cypress domes is everywhere on view.
Photo by Richard
Bryant in The Okefenokee Swamp.
cricket frogs chirrup, pig frogs grunt and alligators growl from within
the grasses. Sandhill cranes utter their distinctive, plaintive squawks
as they fly, with impossible grace, over it all.
Photo by Leslie Edwards
by Chris Bryson
Text by Leslie Edwards.
Geology kindly reviewed and supplemented by John Costello, Georgia Department
of Natural Resources.
Please send comments
Guide to the Okefenokee Swamp, by Taylor Schoettle. Email firstname.lastname@example.org
or call (912) 437-6799 to order a copy before the pilgrimage. Highly
Swamp, published by the Georgia Wildlife Press, Georgia Wildlife
Federation. Highly recommended.
by George W. Folkerts, and photographs by Lucian Niemeyer. Highly
Swamp: Its Natural History, Geology, and Geochemistry, edited
by A.D. Cohen, D.J. Casagrande, M.J. Andrejko, and G.R. Best. Scientific studies.