Posts Tagged ‘Okefenokee Swamp’

The First Ever Ornithological Expedition to the Okefenokee Swamp in 1912

February 6, 2016

In 1912 an expedition composed of 4 Cornell University professors, 2 graduate assistants, the principle of Ithaca High School, 2 Georgia state entomologists, and 4 local guides conducted an ornithological survey of the Okefenokee Swamp.  The expedition lasted from May 6th-July 13th.  They found 75 species of birds, and 19 species were added to their list based on descriptions of the local guides who were considered reliable sources.  At the time of the expedition the Okefenokee was still a vast wilderness of cypress swamps, flooded marshes, hardwood hammocks, and larger islands topped by open pine savannahs.  River bottomland forests grew along the Suwanee River.  A few families lived on the edges of the swamp and within it, but a lumber company was making inroads at the time because they were felling much of the best timber.  The expedition wrongly assumed the swamp was going to be destroyed, like so many other remnants of wilderness left in North America then.  They did not know Franklin Roosevelt would eventually make it a protected wildlife refuge.

The most abundant bird in the swamp was the red-bellied woodpecker followed closely by the crested flycatcher.  Old growth forests provide plenty of food for woodpeckers.  Bobwhite quail were abundant on the larger islands where “pine barrens” prevailed.   Prothonotory warblers were also considered abundant.  The expedition found a rookery consisting of 500 little blue heron nests with eggs.  However, they saw just a few egrets because a recent fashion craze for egret feathers on women’s hats had led to the decimation of this species.  Georgia outlawed egret hunting in 1910.

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The information for this blog entry comes from an article published in The Auk from October 1913.  I purchased this vintage scientific journal from paleopublications.com .

The red-bellied woodpecker was the most abundant bird in the Okefenokee Swamp during Frances Harper’s survey of 1912.

The crested flycatcher was the 2nd most abundant bird during his survey.

File:Everglades Little Blue Heron.jpg

Harper found an active rookery of 500 little blue heron nests in the Okefenokee during his 1912 survey.

The expedition saw 150-200 wood storks feeding in shallow water, and 1 day a flock of 40 bobolinks flew over their heads.  Carolina wrens and brown-headed nuthatches were also considered very common/abundant in the swamp.

Woodpeckers in order of abundance were; 1. red-bellied, 2. pileated, 3. red-cockaded.  Hairy, downy, and red-headed woodpeckers were present but considered uncommon.  Ivory-billed woodpeckers, extinct since ~1945, still occurred in the northwestern part of the swamp on Minne Island then.  A guide heard an ivory-billed call during the expedition, and they found some recently used nests.  Red-cockaded woodpeckers, rare and endangered today, were still common here in 1912.

Ivory-billed woodpecker and nest.  Frances Harper found ivory-billed woodpecker nests in the Okefenokee that had been in use within 3 years of his survey.  One of his guides heard the call of an ivory-billed woodpecker during the survey, but Harper did not see or hear any.

Swainson’s warbler, considered uncommon now, were reported to be “not uncommon” in the swamp during the expedition.  Chimney swifts were a common bird seen hunting for mosquitoes over the water.  Evidentally, large colonies of this bird nested in hollow cypress trees for the local guides said they did not nest in their homestead chimneys.  Other common song birds included grackles, yellow-billed cuckoos, yellow throats, pine warblers, bluebirds, tufted titmice, eastern meadowlarks, and cardinals.

Red-shouldered hawks were the most common bird of prey during the day, while barred owls dominated the night.  Turkey vultures and black vultures were both common and made quick work of skinned alligators killed by hunters.  The expedition found 15 osprey nests.  They also often enjoyed seeing the aerial acrobatics of swallow-tailed kites.

Swallow-tailed Kites

Harper saw flocks of swallow-tailed kites summersaulting above the tree line.

Wood ducks were common year round residents, but the expedition came at the wrong time of the year to see winter migrants.  However, the local guides informed them that hooded mergansers, mallards, and coots commonly wintered in the swamp.  Shy sand hill cranes were  more often heard than seen because the local people hunted the delicious birds whenever they could.  The locals also relished wood ducks.  Oddly enough, white ibises were on the local menu.  I would suppose a fish-eating bird would taste too strong.

Anhingas could be found along the Suwanee River and in some of the larger bodies of water.  One of the guides was blind in 1 eye because his pet anhinga had stabbed it with its bill.

A single loggerhead shrike was seen chasing a bluebird.  A dead bluebird impaled by a shrike was further evidence of this species.

The only species the expedition was surprised to find was the spotted sandpiper.  This bird prefers open shore type habitat, but apparently some individuals were content to forage around fallen logs adjacent to marshes.  Spotted sandpipers winter south of this region and spend summers to the north.  The birds the expedition saw were probably in the process of migrating north.

Remarkably, not a single common crow was seen in the swamp.  The crow is 1 of the most common birds in my neighborhood in Augusta, Georgia, and I always see them wherever a travel.  This demonstrates just how attached crows are to the neighborhoods of man.  They thrive in manmade environments but avoid deep wilderness.  They like to eat human agricultural waste and garbage–a rich source of food compared to what they can forage in deep wilderness.  The expedition did identify a few fish crows along the Suwannee River.

Carolina parakeets became extinct in 1914.  Sadly, this species had been gone for so long from the Okefenokee that none of the old-timers were able to give any personal accounts of their encounters with them.

Reference:

Wright, Albert; and Frances Harper

“A Biological Reconnaissance of the Okefinokee Swamp: the birds”

The Auk 30 (4) October 1913

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Okefenokee Fires

July 19, 2013

The awesome Okefenokee Swamp is so intimidating it even resists the avarice of mankind.  Developers were willing to abandon it to nature lovers in 1937 but not before they logged most of the ancient 400-900 year old cypress trees.  The undrainable labyrinths of swamps, the floating shaky islands of peat, and the frequent uncontrollable fires scared away businessmen who feared they could never make a profit developing this wilderness.    Thus we are left with an amazing gem of nearly pristine nature.

The Okefenokee Swamp has an interesting geological history that I’ve already discussed (See https://markgelbart.wordpress.com/2010/11/19/the-geological-and-ecological-history-of-the-okenfenokee-swamp-part-one/)  Its current incarnation is just 6600 years old, based on an analysis of peat cores.  However, fossil swamp vegetation has been found buried inside Trail Ridge to the east of the swamp.  Trail Ridge is a former barrier island that fronted the ocean 1.8 million years ago.  This suggests swamp has intermittently occurred in the Okefenokee basin for over a million years, but during glacial cycles the water table drops, and it becomes dry land forest mixed with grasslands and only a few relic marshes. 

The frequent peat fires that occur in the Okefenokee basin are impossible for man to extinguish.  They are a surprising example of nature defeating man.  The policy of the fish and wildlife service is to let fires burn inside the refuge.  They do try to protect boardwalks and wildlife viewing towers but were unsuccessful at even this small scale fire defense in 2011.  Outside the refuge a 250 mile long Swamp Edge Firebreak has been constructed.  For the most part it does prevent the spread of small fires.  Neverthelesss, major fires  escape the boundaries of the refuge and destroy many square miles of commercial timber.

MODIS true color and false color images

Satellite image of 2011 Honey Prairie Fire in the Okefenokee Swamp which burned from April 28, 2011-April 12 ,2012 and consumed 318,000 acres.  Most wildlife survived.  Without fire the Okefenokee would succeed to shrub then forest.  Fire here helps maintain diverse habitats and increases biodiversity.

Okefenokee fires are difficult to contain because they are peat fires and can continue burning underground, spreading even if they appear to be extinguished from above.  Major fires in the Okefenokee occur cyclically and have been recorded in 1840, 1860, 1884, 1908, 1932, 1954, 1990, 2007, and 2011.   The 2007 fire is known as the Georgia Bay Complex Fire and it burned through most of the refuge and into Florida.  I smelled smoke from this fire in Augusta, Georgia, hundreds of miles away.

The Georgia Bay Complex Fire burned from April 16, 2007-June 22, 2007 and consumed 600,000 acres.  I smelled smoke from this fire in Augusta, Georgia hundreds of miles away.

Most mature trees survive fires.  The Okefenokee Swamp, as we know it, depends upon fire.  Fire thermally prunes tangled vegetation, giving the refuge its open appearance.  The shallow wet prairies, the most characteristic habitat of the swamp, would succeed to less productive shrub bogs without fire.  There would be few alligators and wading birds here, if fire didn’t occur.

Chesser’s Prairie in the Okefenokee Swamp.  Without fire this open water would become a tangled shrubby bog.

I visited the Okefenokee about 6 years ago, and it was about as disappointing as my trip to the Great Smoky Mountains National Park.  It wasn’t as crowded, but nevertheless seemed devoid of wildlife.  We visited during a drought.  Believe it or not, I saw not a single drop of water in the northern part of the refuge.  I  expected to see lots of egrets and herons and was astonished to see not one.  The only wildlife I saw were gray squirrels, big flocks of robins, and signs of wild hogs rooting.  They did have a nice zoo with alligators, black bears, and snakes.  An otter escaped from its pen and sniffed my shoe.  But they were caged animals, not wild.  Some day, I’m going to visit the refuge again, but I will make sure it’s not during a drought.

Temporal Correlations between Lake Agassiz, the Okefenokee Swamp, and Ancient Flood Myths

January 6, 2011

In last week’s blog entry I discussed the cyclical impact of breaches in glacier ice dams on Ice Age climate.  The biggest glacial lake in North America formed from rapid melting of glaciers at the end of the last Ice Age is known as Lake Agassiz

 

Map of ancient Lake Agassiz.  A glacier ice dam formed this lake which existed from ~13,500-~8200 BP.

As the map shows, Lake Agassiz was bigger than all the Great Lakes combined and at the time of its existence was the largest freshwater lake in the world by far.  About 12,900 years ago a major breach of the ice dam that formed this lake occurred, flooding the North Atlantic with cold freshwater and shutting down thermohaline circulation (as I described in last week’s blog entry).  This event (known as a Heinrich event) triggered a sudden cold snap referred to as the Younger Dryas, named after a species of flower that flourished in Europe during this arid cold phase of climate.  The Younger Dryas lasted for 500 years as earth’s temperatures in the northern hemisphere plummetted back to levels equal those of the last glacial maximum (~29,000-~15,000 BP).

As the climate cooled another ice dam formed stopping the outflow of water, so that Lake Agassiz continued to exist.  But climate gradually warmed again and the final dissolution of the lake occurred about 8200 BP.

Map showing final outflow of Lake Agassiz.  After glacier ice dams broke, the water escaped through tributaries leading to the St. Lawrence River, the Mississippi River, Hudson Bay, and western rivers as well.

The final dissolution of Lake Agassiz also shut down thermohaline circulation, causing a shift in climate to arid and cold, though it wasn’t nearly as severe as the Younger Dryas.  Nevertheless, this time, the dissolution of Lake Agassiz was complete, and scientists believe sea levels rose by as much as 1 meter in less than a year.  It occurred to me that this closely correlates with the period of time when the Okefenokee basin filled with water and became a swamp.  Scientists carbon dating the peat there discovered that the modern version of the Okefenokee became swamp about 7,000 years ago.  This is also roughly the time of modern barrier island formation off the Atlantic coast.  Between ~36,000 and ~7,000 years BP, the Okefenokee basin consisted of open pine savannah and scrub oak interspersed with small scale streams and freshwater marshes, but an increase in atmospheric moisture and the rise of the water table led to swamp development.  It’s likely that swamps periodically developed in the basin and periodically dried out following fluctuations in the water table throughout the Pleistocene.

It’s also been noted that the final dissolution of Lake Agassiz and other glacial lakes all over the world may correlate with worldwide flood myths.

The final dissolution of Lake Agassiz caused sea level to rise by 1 meter in just 1 year.  This would have flooded coastal regions.

The literal story of Noah’s flood is impossible, but it may be based on some truth.  A flood that covered the entire world is geologically impossible, and there is no scientific evidence to support this belief.  But it is likely that the dissolution of Lake Agassiz and glacial lakes in Europe did cause major localized flooding in many areas of the world on a scale far surpassing anything from recent recorded history.

One clue regarding changes in climate patterns resulting from this event comes from Genesis 7:12 in the bible.  “It rained for 40 days and 40 nights.”  The Little Ice Age, a relatively minor climatic event but one that had a major impact on European agriculture for 500 years (1314-1850 AD) began with cold rainy summers–lots and lots of rain.  It’s plausible that the initial flood of freshwater into the North Atlantic caused a low pressure system that drew unusually prolonged spells of cold rain in summer, though, of course, not exactly 40 days in a row.  But it wasn’t rain that caused the flooding.  Instead, it was the sudden rise in sea level that destroyed coastal villages.  Whether or not the villages were morally wicked was coincidental.

Today, Lake Winnipeg and a few other Canadien lakes are remnants of Lake Agassiz.  The Great Lakes formed from melted glaciers in ancient river valleys scoured out by glaciers.  The Great Lakes  formed and reformed many times throughout the Pleistocene, and it’s probable a glacial lake has repeatedly re-occurred on the site of Lake Agassiz as well.

The Geological and Ecological History of the Okefenokee Swamp (part three)

December 3, 2010

Common and Interesting Plants Found in the Okefenokee Swamp

Most of the aquatic  plants that dominate the present day landscape of the Okefenokee Swamp were restricted to small scale marshes alongside the reduced number of rivers and streams that still incised the Okefenokee basin during the arid milleniums of the Ice Age when the water table fell and the swamp dried up between 36,000 BP and 7,000 BP.  The rest of the basin during this time period probably consisted of grassy pine savannah and scrub oak.  Nevertheless, these relic aquatic remnants provided the nucleus of the population that eventually re-established itself as the primary vegetation of the region.  Here are some interesting floral components of this environment.

Bald Cypress (Taxodium distichum)–Eight-hundred year old giants still stand in a few coastal swamps near Georgia’s coast.  One-hundred years ago, when loggers decimated much of these ancient bottomland forests, they skipped over the biggest cypress trees because they were too large and hollow, and therefore too much trouble to economically harvest.  One of these gigantic cypress trees is located in the Townsend Wildlife Management Area in McIntosh County.  It’s 44 feet in circumference.  Imagine 7 men, all at least 6 feet tall, laying end-to-end in a circle around the tree and they still wouldn’t completely encircle it.  It’s understandable but not generally known that cypress trees are relatives of the famous Californian redwoods.  They sure have great size and long life in common.

For more about Georgia’s big cypress trees see this following link  http://savannahnow.com/news/2010-08-30/700-year-old-cypress-tell-story-survival

I took this photo of a cypress tree in autumn foilage at Phinizy Swamp in Augusta, Georgia.  Unlike most coniferous trees, cypress trees lose their foilage in the winter, like deciduous broad-leafed trees.

Unlike most coniferous trees, cypress trees are not evergreen, and they shed their needles in the winter.  They usually live in flooded swamps. They have mysterious knees–wooden knobs that grow above water.  Scientists are uncertain whether these aid in respiration or simply balance the trees in the watery muck where they grow.

Water tupelo (Nyssa aquatica)–Cypress trees hollow out and provide roosting habitat for bats and homes for other animals, but tupelo trees become hollow more frequently.  Matt Clement, a grad student at UGA, found 97 roosts of Rafinesque’s bats along the Altamaha River, and most of them were in hollow tupelo trees.

Water shield or dollar pad (Brasenia schreberi), Floating Heart (Nymphoides sp.), and White Water Lilly (Nymphaea odorata)–These are three completely unrelated plants, but their leaves look similar.  In fact, I can’t really tell their leaves apart.  It’s an example of convergent evolution when different species evolve similar structures to solve the same ecological problems.  All three are what people think of as the lilly pads so commonly seen floating on the surface of the open water habitats in the Okefenokee Swamp that are often confusingly referred to as prairie because they’re treeless.  All three species have round floating leaves attached via long stems to underwater roots.

Panic grass (Panicum sp.) Saber-tooths and jaguars lurked hidden in patches of this tall cane-like grass, stalking the long-horned bison and horses that fed upon it during the Pleistocene.  The large fauna are gone but the flora remains.

Photo of some panic grass also known as maiden cane that I took at Phinzy Swamp, Augusta, Georgia.  There was another patch on the other side of the path that was 12 feet tall.  I wish I would’ve taken a photo of that.

Spanish Moss (Tillandsia usneoides)–Oddly enough, Spanish Moss is related to pineapple–both are Bromeliads or air plants.  Wind and birds spread seeds and fragments.  The seeds and fragments of the Spanish Moss lodge in other tree branches.  The Spanish Moss then grows (both from seed and vegetatively).  The plant survives by extracting nutrients from air and rain water, not from the trees upon which they land, thus they’re considered epiphytes, not parasites.  Birds, bats, spiders, and snakes live in and about the moss.

Spanish Moss hanging from either a water or laurel oak at Phinizy Swamp, Augusta, Georgia.  Spanish Moss is quite common in the lowlands of the Augusta area, but I’ve never seen any in hilly sections.

Bladderwort (Utricularia sp.)–Like strange creatures from a low budget horror film, carnivorous plants thrive in the Okefenokee Swamp.  Bladderwort is an underwater plant with no roots.  The bladder-shaped structure on the plant works like a trap door, a suction-on-contact action captures fish fry, mosquito larvae, tadpoles, and protozoa.

Pitcher plants (Sarracenia flava, Sarracenia mino, Sarracenia psittacaea)–There are three species of pitcher plants found in the Okefenokee–the hooded, the parrot, and the golden.  A sweet rotten odor emanating from the plants attracts insects which get trapped in tubular stems.  Backward hairs block insects from being able to escape, and eventually, they tire and fall into the toxic water at the bottom of the tube.  Bacteria in the water digests the insects, releasing nitrogen that the pitcher plant is able to absorb.

Round-leafed Sundew (Drosera rotundifolia)–The sticky hairs on this plant work just like flypaper, trapping hapless insects.

Burreed (Sparanium sp.)–Fossil mastodon dung discovered in the Aucilla River, Florida contains many types of aquatic plants, including most discussed here.  Cypress was the most common item in their diet, but the beasts ate nympoides, nymphaea, and this one–burreed.  Burreed is an important plant in the second stage of forest succession that occurs when islands develop within the swamp.

The five stages of forest succession in the Okefenokee Swamp

1.  Sphagnum moss floats to the surface of open water and soil begins to accumulate on it forming an island.  Beakrush takes root.

2. Burreed, panic grass, and redroot are the second stage of plants to colonize the island.

3. Sedges take over.

4. Bushes and saplings colonize the island.

5. Trees such as cypress, tupelo, water oak, and pond pine form the final components of island forest succession in the Okefenokee Swamp.

The Geological and Ecological History of the Okefenokee Swamp (Part One)

November 19, 2010

Dupont Corporation’s plan to mine titanium from heavy mineral sands in Trail Ridge, which borders the eastern boundary of the Okefenokee Swamp, sparked a crash course study of the geology and ecology of the Okefenokee Swamp.  Scientists and environmentalists feared the impact of the mine could have seriously degraded the swamp.  The potential environmental degradation was so feared, that even conservative politicians opposed the project, and ten years ago Dupont agreed to abandon the proposal and sell the land to the state and the Nature Conservancy.  But the resulting research papers provided a wonderful source of knowledge and excellent fodder for my blog.

The Geological History of the Okefenokee Swamp Basin

The existence of the Okefenokee basin is due to many different geological factors.  It’s located in a region known as the southeast Georgia embayment.  This area was submerged under the Atlantic Ocean during the Cretaceous and for most of the Eocene.  During the Eocene, sediment intermittently began to be deposited, but late in the Eocene, strong ocean currents are believed to have washed these away.  U.S. Geological Survey bore holes near the Okefenokee Swamp reach late Miocene strata about 65-70 feet below the surface.  This strata consists of limestone pitted with the impressions of fossil sea shells–evidence that as recently as 5 million years ago, the southeast Georgia embayment was still periodically inundated with sea water.  Above this limestone layer is an impermeable clay of Pliocene age.  Here we find two reasons for the Okefenokee basin’s existence: the basin sagged because rainwater caused the limestone bedrock to dissolve (albeit unevenly) in a process known as karstification, and the clay layer above this prevents water from draining, thus providing the optimum conditions for wetlands to develop within the basin.

Hardwood hammocks, the islands within the swamp, are elevated above the basin.  These were formed during the late Miocene/early Pliocene when the area was still under sea water.  Ocean currents and river sedimentation built these little islands.  Later, when the basin emerged above sea level, the islands remained in place as dry land humps in the swamp.

The southeast Georgia embayment emerged above sea level during the Pliocene, and the resulting geological uplift caused the Suwanee River to backflow and reverse course, providing the source of all the fresh water accumulated there.

Map of Georgia’s Pliocene shoreline.  The present day location of the Okefenokee Swamp was submerged under the Atlantic Ocean.  The Suwannee River flowed from west to east.  After the emergence of the Okefenokee Swamp basin above sea level, geological uplift caused the Suwanee River to back flow into the basin and reversed its course, so that it flows west instead of east.  Note the islands which later became hardwood hammocks. Illustration from ‘The Geological and Natural History of the Okefenokee Swamp and Trail Ridge’ by Rich and Bishop.

Some scientists hypothesized that the early Okefenokee Swamp basin was a massive estuary and salt marsh, but there’s no evidence of this.  Instead, evidence from the nearby Trail Ridge to the east of the swamp suggests the basin has been a freshwater swamp since early in its existence.  Trail Ridge  was originally a massive barrier island 130 miles long which is far longer than any current barrier island off the Atlantic Coast, the longest in Georgia being Cumberland Island which is a mere 16 miles long.  Cape Hatteras off the North Carolina Coast is only 48 miles long.  Trail Ridge runs from south Georgia to North Florida as the following map will show.  This geological feature too contributes to the back flow of water into the swamp but is considered a minor influence compared to geological uplift, limestone sinkage, and the impermeable clay layer.  Scientists have discovered fossil freshwater swamp vegetation buried under Trail Ridge sands–evidence that a swamp already existed in the area late in the Pliocene when the barrier island that is now Trail Ridge first formed during a high stand of the Atlantic Ocean.

Trail Ridge is the oldest terrace on Georgia’s coastal plain.  Terraces run parallel to the Atlantic Ocean and were all formerly barrier islands that formed during warm interglacials or interstadials when sea level was higher than that of today’s.  Logically, the oldest terraces are further west because subsequent high stands of water would have washed younger ones away.

Map of Pleistocene terraces on the Georgia coastal plain.  Terraces were barrier islands formed during warm climate cycles when sea level was higher than that of today.  From west to east they are aged  from oldest to youngest.  Scientists  name  these terraces.  The following is a list of the terraces and their estimated ages.  (Note: scientists don’t always agree with these age estimates.  I’m using those from a college thesis that I list in my references.)  The Wicomicico Shoreline (Trail Ridge)–1.8 million years; the Penholoway Shoreline–780,000 years; the Talbot shoreline–240,000 years; the Pamlico shoreline–130,000 years; the Princess Anne shoreline–80,000 years; and the Silver Bluff shoreline–40,000 years.  The Talbot shoreline formed during the Yarmouthian interglacial.  The Pamlico shoreline formed during the Sangamonian Interglacial.  The Princess Anne shoreline formed during the early Wisconsin Ice Age when sea level was dropping but paused during an interstadial.  The Silver Bluff shoreline also formed during a pause in sea level drop caused by an interstadial.  Eventually, during glacial cycles, the shoreline could be located as much as 50 miles to the east of where it is today due to a lowering of sea level when much of the planet’s water was locked in ice.  Pollen and fossil wood has been recovered from Grays Reef, 11 miles off Sapelo Island, showing that forest and prairie grew in areas deep under water today.  It’s interesting to note that the Silver Bluff and Princess Anne shorelines formed when ice core data suggest temperatures were cooler than those of today.  I think this shows that a certain threshold must be met before sea level fell drastically during glacial cycles.  The sea level had been falling during the Wisconsin Ice Age but paused when the climate warmed up, even though it wasn’t as warm as that of today.  It also shows that sea level lags behind climate change by thousands of years.

The Ecological History of the Okefenokee Swamp Basin

The Okefenokee Swamp apparently has existed since the late Pliocene, but it has been an intermittent existence.  During the Pleistocene whenever there was a cycle of glacial expansion, the climate became cool and arid.  Sea level retreated many miles to the east and the water table fell, causing the Okefenokee Swamp to become a relatively dry basin.  Instead of hosting primarily wetland vegetation, oaks and pines and grasses grew in the basin.  Wetland species such as cypress, tupelo, and water lily, still existed but were relegated to small scale marshes bordering the rivers and streams that still incised the basin.

Some time during a glacial cycle, wind and remaining water eroded 4 elliptically shaped Carolina Bays into the swamp basin.  The bays, along with the remaining rivers, provided relic habitat that allowed wetland plants to rapidly recolonize the basin when climatic conditions once again became favorable to swamp development.  Scientist have taken cores of the peat in the swamp and discovered that the peat in today’s Okefenokee has only been accumulating for 6600 years.  It’s likely the Okefenokee basin was dryland habitat from about 36,000 years BP to about 7,000 years BP.  The last glacial maximum, the coldest and dryest climate cycle of the late Pleistocene, lasted from 28,000 BP-15,000 BP.  So it took thousands of years for the water table to rise to swamp level again, following the drying out of the swamp during the Ice Age.

References:

Rich, Frederick, and Gale Bishop

Geology and Natural History of the Okefenokee Swamp and Trail Ridge, southeastern Georgia and northern Florida.

Georgia Geological Society Field Guides 1998

http://etd.lsu.edu/docs/available/etd-03292006-161251/unrestricted/Willis_thesis.pdf