It sounds simple, the annual cycle of life in Corkscrew Swamp;
but the wife of an Audubon ecologist discovers otherwise.It sounds simple, the annual cycle of life in Corkscrew Swamp;
but the wife of an Audubon ecologist discovers otherwise.
I stepped out of our truck to the exotic racket of boat-tailed grackles and the warm December sun slanting on the gold-green grass. Inhaling soft piney air, I looked around. A figure in khaki was walking past a rustic gatehouse, triggering a faint memory: a camp counselor coming to tell me it was time to go home to the city. Then it hit me. This is no mere vacation -- we really are going to live here.
My husband, Mike, had been hired by the National Audubon Society to do an ecological analysis of Corkscrew Swamp Sanctuary in southwest Florida. The project was to be financed by a Rockefeller Foundation grant to the University of Florida Center for Wetlands. The center was doing a study on the potential for the use of cypress domes as a kind of natural sewage treatment system, and it wanted to augment its information on these pondlike systems with studies of a riverlike cypress strand similar to that preserved in Corkscrew. The National Audubon Society also hoped to get some useful information on better ways to manage its sanctuary. So our basic assignment was to study the sanctuary's 11,000 acres and find out how the ecosystem works.
The figure in khaki was Jerry Cutlip, the sanctuary superintendent, who showed us to our quarters and began helping us to unload our luggage. The last slivers of sun were slipping through the gray cypress trees when I thought I heard a dog howl in the distance. But Jerry suddenly stopped. "Listen!" he said.
The sound came again: hoohoo-hoohoo hoohoo-hoohooaw.
"The barred owls are calling," he said.
"Really?? I asked, half-incredulous and already half anticipating impressing some newcomer with my woodsmanlike knowledge of the owl's call.
So it went for the first few months. We picked up countless bits of information and slowly began to block in a ragged picture of the swamp ecosystem. The real key to Corkscrew lay not in any of its marvelous creatures, like the barred owl, but in a simple chemical compound, H2O: water.
In spring, water is so scarce everyone scans the sky, hoping to see thunderheads replace the columns of smoke from wildfires. For by March the rain-bearing cold fronts have become less and less frequent, and hot dry winds blow each afternoon. The bald cypress respond to the spring heat by covering their nakedness with a feathery green cloak of foliage, sucking moisture from the peat around their buttressed bases. And the swamp dries down like a giant bathtub with the plug pulled.
In April it gets worse. Shallow marsh ponds hold only great curling scales of mud, pockmarked by the tracks of raccoons, and herons come to feast on doomed fish. From the camp centers of the deeper ponds a fish scent rises to mingle with the ever-present smell of distant smoke. Indeed, drop a match into the pondside clump of brown sedges and flames will sweep across the marsh, sputtering and crackling through the sawgrass as if it were so many acres of crumpled newspaper, perhaps sending fingers of fire into the cypress forest to eat the very peat from the roots. Peat fires may continue to burn underground, smoldering for weeks, unextinguishable -- until the rains come.
But come they will. Maybe not in May. Maybe not until late in June. They may start slowly -- tall clouds far off to the east toward Okeechobee one afternoon, a report of rain at Immokalee the next; then we get a fitful little thundershower, two the next week, then three, until a daily rain pattern is established. Or a tropical depression that doesn't qualify for a hurricane can roll in off the Gulf of Mexico and deliver an instant wet season. Either way, there soon will be a regular cycle: little cottony clouds soak up moisture from the bright steamy mornings, and great gray anvils fling it back each afternoon.
Our first rainy season at Corkscrew was sudden. We woke up one dark June morning to a rumbling, heaving sky dripping on a desertlike vista of yellowed wiregrass, dotted with clumps of saw palmetto, and fire-blackened slash pine stumps. By evening the world looked like a vast sheet of hammered pewter. We pushed our canoe off the back step and paddled around in the rain, shouting and laughing.
I say we shouted -- normally we are not raucous people, but there was no other way to be heard above the frogs. With their mating time finally come, their uproar was incredible: bleating squirrel treefrogs, booming pig frogs, yapping barking treefrogs, clucking southern leopard frogs, all surpassed by the high-pitched tambourine music of the oak toad -- like some strange shrill machine with a loose wheel. Out in the midst of the frogs, the sound was painfully intense, but I was caught up in the sensation of a monumental event and as exhilarated as I've ever been by a Fourth of July brass band.
Not all of Corkscrew's creatures were rejoicing at the rain. The mound on which our trailer sits became a refuge for armadillos and dusky pigmy rattlesnakes, which, having had the run of countless acres all spring, were suddenly confined to whatever dry islands they could find. We gently deported the snakes, via a garbage can we keep handy for that purpose, to Eagle Island, a seldom-visited part of the sanctuary with high pine-palmetto habitat. But we could not help the other animals that suffered when the water came up: infant killdeer not yet strong enough to travel far from their flooded nests, glass lizards forced to run a gauntlet of predators as they searched for new hiding places, wood storks whose feeding ponds had coalesced into a vast sea, scattering their fish dinners over miles of the Florida countryside.
A dry season and a wet season. It sounds simple.
But ecologist have learned that timing and distribution of water are critical in a swamp. Here, as in every ecosystem, all plants and animals are in constant competition for limited resources of solar energy and mineral nutrients, and each change in the weather makes life easier for some and more difficult for others, finely adjusting the balance of that perpetual struggle. If a swamp is flooded for too short a time, aquatic organisms may not have a chance to reproduce. Unseasonable rains, on the other hand, can drown out a species that requires a dry period to complete its life cycle. We had to find out what the normal range of variations was -- how much stress the system was prepared to take in stride -- before we could understand which man-made changes might overwhelm and alter the swamp.
First, we set out to learn about Corkscrew's climate. Near sanctuary headquarters we installed a weather station with a thermometer that recorded each day's high and low temperature, a hygrothermograph to measure relative humidity, an evaporation pan, and a rain gauge. And to find out if the weather was the same in outlying areas, we put recording rain gauges at Little Corkscrew Island to the north, at Camp on the west side, and on the South Dike along the sanctuary' lower boundary. We found that although every place on the sanctuary does get about the same amount of rainfall, it doesn't fall everywhere at the same time. Little Corkscrew Island, two miles away, might receive five more inches of rain than our headquarters in a given month, but the reverse could occur just as easily.
One storm sticks in my memory as a vivid illustration of how intense and local Florida thunderstorms can be. It started at three o'clock on June afternoon with a darkening sky tinged with ominous bruiselike shades of sea green and eggplant purple. With no more warning than a few preliminary thunder rolls and lightning flashes, the wind and rain charged across the palmettos and collided with the trailer, battering it with enormous drops. For half an hour I listened to the roar of rain hammering the windows and watched palm trees turn inside out and pine branches fly by, still airborne when they disappeared into the silver curtain of rain. I paced the floor, knowing better than to stay in a trailer during anything resembling a tornado but reluctant to step outside when objects -- including jagged pieces of sheet metal -- were soaring by.
When it was over, and the still air was a peculiar late-afternoon yellow, I walked out to survey the damage. Mike had been three miles away on the South Dike all afternoon, so I was relieved to see his truck pull up outside and hurried out meet him.
"You're all right?" I asked anxiously.
"Of course I'm all right. Why shouldn't I be? What's going on out in the road with all that sheet metal?"
"Those are pieces of Lowery's barn that blew apart in the storm."
"What storm?"
"What storm" We had the most awful thunderstorm I've ever seen in my life. It was like the movies you see of hurricanes!"
"Oh. It didn't rain where we were."
Because Corkscrew is so flat -- the highest spot is only five feet above the bottom of the deepest lake -- water sometimes actually runs upstream after a heavy local shower, spreading in all directions to even out the "mound" of water dumped by the storm. Indeed, the hydrologic processes invoked by seasonal rainfall on flat terrain created and now maintain Corkscrew Swamp.
Horseshoe Marsh, in the south-central part of the sanctuary, was once a pass through a great coral reef.
About two million years ago the water receded, leaving the former reef miles inland and covered with a sandy soil that probably supported an oak savanna habitat resembling today's African plains and, like them, populated with large grazing animals: bison, mammoths, horses, giant armadillos, and enormous tortoises. By about 5,000 years ago the sea level had risen and rainfall had increased, permitting freshwater to fill the old reef channel and peat began to form in the deeper places. Since oxygen, necessary for the decay process, is in low supply in the swamp waters, vegetation fragments accumulate instead of decomposing as they do in terrestrial environments. Over the years, the Horseshoe Marsh peat deposit built up and blocked the channel, forcing water out to the sides and creating the habitat pattern that is the hear of Corkscrew Swamp as we know it today: a horseshoe-shaped riverlike cypress strand branching to the south around a slightly elevated sawgrass marsh.
In an ecosystem with hills and rivers, basic hydrology is not too difficult to understand: rain falls and drains into little streams that run into bigger streams. The bigger streams drain into rivers and so on, eventually, into the ocean.
But this is not what happens at Corkscrew. When it rains here it is like spilling a carton of milk on a old linoleum floor. The water seems to spread everywhere at first, then begins to seek out the faint indentations between the floorboards and flows slowly along them toward some imperceptibly lower point.
Southwest Florida's floorboards are a series of broad geologic folds that run northwest-southeast across the Big Cypress region. These rock ridges have eroded, and the valleys between have filled in with sand and peat. The result is a landscape so flat that water cannot develop sufficient gravity-aided erosive power to carve out river valleys and instead spread overland and travels slowly to the sea as sheet flow.
But how do you find out how much water goes where and when if there are no streams on which to install flow gauges? We had to find a way because this information was critically important to Corkscrew Swamp's survival. A canal system draining 390 square miles of swampland for a residential development called Golden Gate Estates had been constructed south of Corkscrew, and in 1965 a major canal was extended to within three miles of the sanctuary boundary. Droughts and consequent fires had been unusually severe, and shrubs were beginning to invade the marshes. Drainage apparently was destroying Corkscrew Swamp. Following recommendations of hydrologic engineers, Audubon installed a dike to retard the flow of water to the south and a set of pumps to supplement that coming from the north. But the vegetation continued to change. When we arrived in 1973, the big questions were: How bad is the drainage problem? And what can be done about it?
We decided to orient our study around four transects that pass through representative examples of all the major Corkscrew habitats: pine-palmetto, myrtle prairie, marsh, cypress, slough, and hammocks of hardwood forest.
In each habitat, along each transect, we sank a pipe and began recording weekly measurements of groundwater levels inside the pipe and surface water levels outside.
When I went out to check water levels, I preferred to travel on horseback.
From our place on Sanctuary Road, I would ride north through wildflower-sprinkled cutover pineland and cut across Ira Capelle's ranch. I usually saw a few turkey vultures and bobwhites, and occasionally a rabbit or a corn snake, but in summer the mosquitoes could make the ride miserable. Bahia grass pastures must be one of the world's great mosquito habitats. They surely produce many more mosquitoes than the cypress forest. In fact, it is a widely held misconception that swamps swarm with mosquitoes. It is the borders of swamps that are full of them. In the heart of the strand, where the dark water is knee-deep, I have never known mosquitoes to be more than an annoyance.
When you think about it, it makes sense. The fish that eat mosquito larvae almost always have access to the swamps deeper sloughs, but few find their way into the shallow puddles that form in pastures during the rainy season. And it is only during the wet season that there is a problem. When the water first comes up and fills the marshes, both mosquitoes and fish go into a reproductive orgy, expanding their populations to utilize the newly available habitat. The gambusia, or mosquitofish, give birth to live young, which are themselves ready to reproduce just weeks later. But the mosquitoes need only a few days to get off a new generation, so they multiply faster, and soon there are more larvae than even the gluttonous gambusia can devour. For a few weeks the mosquitoes are a plague. But soon the fish catch up and cut their populations back to minor nuisance proportions.
Where I stopped to open the sanctuary gate, a culvert spills into a purple-black reflecting pool bordered with water hyacinths and usually ornamented by a great blue heron, which would come splashing and squawking to life and circle overhead as I approached. Dragonflies would hover over the pool eating mosquitoes, then pause to decorate the pickerelweed, like art nouveau enamel brooches of emerald green, powder blue, orange-gold, and magenta.
Just down the road is the fish farm, biologist Jim Hansen's research project. This is an experimental wood stork feeding area, where small fish are raised in ponds constructed so that the water can be lowered to proper stork-feeding depth as necessary. Wood storks feed by touch rather than by sight, wading about and waving their sensitive bills in shallow water and snapping up whatever they touch. Consequently, unless they find ponds dried down into a virtual fish soup, they do not get enough to eat. In the old days they seldom had problems. In summer, there were fish-producing marshes everywhere. Then, when the rains stopped in the fall, the fish would move into ponds that would gradually dry down, the bulk of them reaching the proper depth for the storks during the late winter nesting season. Now canals have reduced the marsh areas, and the ponds that remain often go dry before the critical weeks when hungry young storks are gathering strength to leave their nests. Stork populations have plummeted. Where once there was the clamor of the young in tens of thousands of nests in the weather-beaten giant cypress trees ringing Horseshoe Marsh, now only about 3,000 pairs breed -- and that in a good year. The Audubon fish farm cannot feed all of the storks all the time -- each pair needs around 440 pounds of fish per nesting season. But maybe we can help a significant number of them get through an occasional crisis period. And it is marvelously satisfying to see hundreds of storks feeding in the ponds, all swaying and flapping about, then one after another taking flight and sailing off toward the rookery. The first time I saw these birds I thought (blasphemous idea) that they were grotesque and ugly, but when they take to the air they are transformed -- from frog into prince, as it were.
When I reached the north end of the fish farm I would turn east onto Little Corkscrew Island, a hodgepodge of ill-defined upland habitats. Cabbage palm is clearly the island's dominant plant, but in some places it is mixed with moss- and fern-bedecked live oaks in a picturebook Floridian hammock setting. In other places the palms grow among pine and palmetto or are scattered over little prairies, interspersed with wax-myrtles. The vegetation is thick enough to lend each bend of the sandy trail a bit of suspense, and on a hot afternoon, the earthly herbal scent of the air and the buzzing and wailing of cicadas make it seem an especially good place to be.
Often I encountered deer browsing in little patches of prairie. If I advance slowly, neither they nor my horse objected. But if I came upon them suddenly and startled them, they were off instantly, just a flash of white tails, leaving my gelding terrified and trembling. It was here, too, that Ed saw the panther.
Mike and his assistant, Ed Carlson, were changing the water-level recorder chart when they heard the rustle of dry palm fronds behind them. They both looked up and saw nothing. Mike had turned back to his work when Ed exclaimed, "Look, a panther!" The animal took one swift bound across the road and disappeared soundlessly into the brush. Mike and Ed ran toward the spot, hoping for a better look, but could find only tiny deer tracks in the loose sand.
The recorder they were working on is one of five permanently installed to give a continuous record of sanctuary groundwater. Two portable recorders are moved form site to site to double-check the weekly readings and measure the reactions of different habitats to rain and evapotranspiration.
Evapotranspiration, the combined effect of evaporation and transpiration, or plant breathing, is an important concept to understand in South Florida because it is what happens to most of our rainfall. It takes so long for rainwater to travel overland that only about ten percent of it ever reaches the sea. Spread out in a think sheet, it is vulnerable to wind and heat, which evaporate it, and to plants, which transpire it into the air. Plants do not just dissipate the water, however. They provide shade and shelter to protect if from evaporation. But where is the balance point? Is it the same with all kinds of vegetation at all times of the year? Does it matter if a swamp grows cypress or Australian melaleuca trees -- or even condominiums? No one really knows at his point.
The Little Corkscrew water-level recorder is where the Grapefruit Island transect begins. From there I would ride northeast, across a tiny pocket of marsh that becomes a thick carpet of iris in spring, then through a hammocky glade haunted by black-and-yellow-striped heliconian butterflies whose sheer elongated wings seem to vibrate rather than flap.
The next well I checked is a Mud Lake Marsh between no Name Island and Grapefruit Island. Named for the solitary old grapefruit tree there, Grapefruit Island is a true tropical hammock with Caribbean trees like hog plum, prickly lime, coral bean, and satinleaf. Here is where I feel like a real jungle explorer. From the outside the thick canopy of palms, oaks, maples, and strangler figs looks like a puffy dark green mound, but in the filtered light of the interior, warm browns and grays predominate. Here, where fire seldom enters, the cabbage palm trunks are crosshatched with old frond stalks or "boots" garlanded with serpent fern and lush poison ivy. My favorite spot is near the grapefruit tree, where a big gumbo-limbo is locked in an incredible sculptural embrace with a huge strangler fig. The gumbo-limbo looks like a fairy-tale tree with its sausage-like rounded branches reaching out at oddly graceful angles from a varnished copper trunk and supporting an umbrella of drooping yellow-green foliage. The strangler fig, a rubber-family cousin to the banyan, isn't really a parasite. Its small fruits, of little concern to humans, are relished by birds, which carry them into the treetops. There, in a bark crevice or perhaps a palm boot, the seeds sprout and a small shiny-leaved tree begins to grow, functioning as a harmless epiphyte or air plant, like an orchid or bromeliad. If all goes well, the fig will soon drop liana-like roots to the ground and begin gathering nourishment from the soil. Folklore has it that as the fig grows, sending larger and larger roots spiraling around its host's trunk, it eventually strangles the original tree, but competition for light is the real problem.
But there is a more significant question here than the fate of one gumbo-limbo. Why is there forest on these islands at all? Tiny bits of white rock are a clue: limestone. Bedrock is only eight inches down. The hardwood trees of a hammock cannot tolerate extended inundation, so they will not grow in the swamp proper, and because they are easily killed by fire, they do not survive to maturity in the pinelands. But hardwoods can flourish where a limestone outcrop juts from the otherwise low terrain, creating a flood-free site with a moatlike firebreak of surrounding wet habitat.
Ruess Island is the last well on the transect, but I usually rode from there to Seven Culverts to change the water-level recorder. Occasionally, as I passed through the oak woods at the north end of Little Corkscrew, wild turkeys would erupt from the brush and race down the trail ahead of me before crashing off into the palms. Just before Washout Road, there is an oblong stretch of prairie where I first saw swallow-tailed kites -- flying low, tilting, gliding, and dipping like a kite -- such perfect birds I had to reassure myself I wasn't dreaming.
The Seven Culverts channel water under Washout Road, a fortuitously situated access road that crossed the main direction of flow and forces water entering the sanctuary through openings where it can be measured easily with a current meter. The South Dike does the same thing with water leaving to the south. But how do you determine how much water enters and leaves by other routes? As there is nothing to constrict the sheet flow, this water never develops enough velocity to register on a current meter.
We had reasonable figures for water coming into the sanctuary as rainfall and exiting via evapotranspiration, but we had to find a way to measure the sheet flows before we could develop a water budget. And a water budget -- a set of calculations telling how much water comes into the system and where it all goes -- is what ties the whole picture together in an ecosystem hydrology study.
The flow-measuring instrument we devised was ridiculously simple: a yardstick and a sprig of bladderwort. You just measure the speed at which a piece of bladderwort -- with its little air sacs for trapping insects -- drifts a yard and use that figure, the depth of the water, and the shape of the channel to calculate the volume of low.
Such imprecision may horrify engineers with their delicately calibrated instruments, but a reliable estimate is all that is practical when you are working with something a large-scale and variable as an ecosystem. measuring fine detail is prohibitively expensive and usually so artificial as to be misleading.
Calculating groundwater flow is more difficult. We have done soil profiles at all our well sites, so we have an idea where the water-bearing strata are, but estimating how much water is down there and where it is going will require a lot of complex hydrological figuring.
I didn't think about technical difficulties like this, though, when I was riding along Washout Road. I listened to the clucking of green herons and, where tall plumes of dog fennel line the tire ruts, I watched lubber grasshoppers -- three-inch monsters of orange, gold, and black with herringbone-patterened jumping legs -- clinging to the bobbing branch tips munching industriously with their multiple mouthparts.
Once I was startled by what I though was an explosion. Out of the corner of my eye I could see a cloud of smoky brown and white fragments -- white ibis. I stood motionless as hundreds and hundreds of them billowed overhead, the roar of wingbeats giving way to an ill-organized chorus of nasal honking, and they slowly spiraled back onto a flag pond, one of those mucky sloughs filled with fire flag -- a relative of the banana with big exotic triangular leaves on long fleshy stalks.
I don't know whether the ibis would have felt safe to resume feeding had I been on foot instead of on horseback. But I feel certain I never would have seen the wild boar. I had stopped along the western edge of Little Corkscrew to focus my binoculars on a distant hawk and had been sitting there for several minutes when I heard a movement in the tall grass across the canal. I turned my head slowly and watched the tusked snout of a wild hog push through the grass fifteen feet away. He stepped out onto the mud bank and peered about with glittering little eyes. I stood perfectly still. Dusky brown and lean, looking far more like a truly wild western peccary than what he really was -- a feral descendant of the domestic pig -- he dropped his head and began rooting in the grass. My horse swished his tail. The hog snapped to attention, staring intently in my direction. Perhaps he figured the horse was a cow, because he soon turned his attention to grubbing in the mud, and after a few minutes of watching, I too went back to my own affairs.
When I came to the bend in the road north of the fish farm, I would look to see if the big alligator was sunning in his usual spot. Actually, there are several twelve-footers there, but the real grand daddy probably is the one that lives beside a well on the south Dike transect. Despite the fact that I know unfed, unmolested alligators are peaceable, it still make me nervous to cross the wobbly one-board-wide footbridge across that canal.
On up the road, where the fish farm borders Eagle Island, I once encountered a four-foot eastern diamondback rattlesnake. As I watched the massive animal ripple slowly across the road, majestically aware it had the right-of-way, I was struck by the sobering realization that its brown, gold, and black diamond pattern would be indistinguishable among weathered stems of redroot and maiden-cane. That is the real worry about snakes, accidentally stepping on one. Florida snakes don't bother you unless you pick a fight. Once, walking through dense ferns, Mike even stepped on a cottonmouth and got it hung up inside his pants leg -- and the moccasin never attempted to bite.
Usually I went home by way of Fish Farm Road, which runs west across the myrtle prairies and south of Eagle Island, through a wispy strand of cypress, and out onto the North Marsh. once home, I would unsaddle my horse and hose him down, then make a pitcher of lemonade to drink while I copied the water-level records from my data book.
Each Wednesday night all those involved in the project would bring data, recorder charts, complaints, suggestions, demands, and bright new ideas and unload them all on Mike.
It was his job to come up with theories for us to pick apart until we arrived at one that fit all the data collected.
That is how it worked with the water-level data from the lettuce lakes. Everyone who visits Corkscrew remembers and loves one of these, First Lettuce Lake, where a chartreuse carpet of water lettuce, a floating plant that looks like a small, loose-leave cabbage, stretches out across a picturesque pond apple slough to a tiny island with a tall cabbage palm and a big alligator on it. Every day for fifteen years sanctuary personnel have been measuring water levels at these lettuce lakes.
Mike tried to use these records to calculate how much the drainage from the new canals had increased the severity of the droughts in Corkscrew. He reasoned that if he graphed dry-season water levels from the lettuce-lake records on a vertical axis against rainfall on a horizontal axis, the points would fall in a line if rainfall were the only determinant of water levels. However, if rainfall was of lesser significance, the points would be scattered. But if the dots for the early years, before canals, dike, and pumps, fell in a line and the recent points followed a different pattern, it would indicate that rainfall had controlled water levels under natural conditions but some new factor or factors had become significant. And that is what the graph showed. But the line did not break up until after the dike and pumps went in. The canals were not what changed the relationships between water levels. There was no evidence of increased drainage.
But what about wet-season water levels and hydroperiods and rates of dry-down? Mike analyzed these records by month and by season, even ran the information through the University of Florida computers. And all the answers came back the same: There was no detectable difference in levels at the lettuce lakes before and after construction of the Golden Gate canal system.
So we performed the logical experiment: We shut off the pumps and opened the dike culverts and monitored water levels for two more years. This time we found normal wet-season conditions, but dry-season water levels were slightly lower than expected, and there was a somewhat accelerated rate of dry-down. It still does not look as if we have a serious drainage problem, but something seems to be happening downstream. Our best guess is that the large North Golden Gate canals several miles southeast of us recently have intercepted a groundwater flow channel. We have found there are shell beds leading off in that t direction, and we are now trying to raise funds for more detailed studies of the groundwater flow routes.
The hydroperiod data from our wells explained why willows were invading the marsh.
People had always thought water depth was the critical factor n a swamp. But our data show that the length of time surface water is present -- the hydroperiod -- is much more important. We found that each habitat type has a distinct and consistent length of hydroperiod. The part of Horseshoe Marsh where the willows were coming in had been thrown hydrologically into the cypress-willow range. Apparently the dike had been holding water in the marsh too late to permit it to burn as frequently as necessary to inhibit shrub growth. The willows seem to be a successional species setting the stage for eventual cypress forest.
In theory, to keep the marsh area open, you manipulate the dike so that the marsh gets dry enough to be control-burned regularly. But if you want cypress, you leave the dike alone and keep fires out. The dike has adjustable culverts that make it easy to test such hypotheses, and it serves as an access road for fire-fighting equipment when we do need it.
This could be important, because even under natural conditions cypress swamps do burn. We have found evidence of fire everywhere in Corkscrew. We even think the lettuce lakes were formed by peat fires. So what is there to be upset about? If fires are natural, just let them burn. They seldom kill cypress anyway. True, and occasional fire gets out of hand and burns out the peat and the roots and destroys a strand. This has been happening for thousands of years. But now we have only this one great cypress strand left. All the others have been logged. Should we protect it, plow firebreaks around it, guard it, and not let a spark near it? If we do that it won't remain cypress either. Because without a light, cleansing fire each century or so, the litter of cypress needles, broken branches, and dead fern fronds will build up a mound of peat, and hardwoods will come in, eventually dominating the cypress and converting the swamp into a hammock forest.
Whatever we do, nature probably will overrule us and decree when the cypress shall burn, but we are the ones who had to decide about the pumps. We knew we could not run them every dry season because a cypress forest needs to go dry every once in a while in order for seeds to germinate. In a permanently wet forest, there are no young cypress, and after five or ten years of continuous flooding, even the mature trees begin to look decrepit.
If the pumps were out somewhere on the north end of the sanctuary, what we did with them would not matter so much. The land could go dry, and visitors -- many of whom never have seen this kind of environment -- would not be shown that area as an example of "what a swamp is really like." However, the marvelous old strands of cypress, the visitors, and the water pumps are all in the south end of the sanctuary, where the boardwalk is.
I think of the boardwalk area as the enchanted forest.
That may sound corny, but I have searched for another word and cannot find one that describes the special feel of the forest. The animals there have no fear. They are not fed and do not beg, except for a pair of fundamentally dishonest fox squirrels. Despite the presence of 40,000 visitors a year, the animals are not supplicants groveling and performing to manipulate human "benefactors." They remain proud and wild, and visitors do not have to sneak up on them or hide in blinds or even whisper. The animals know you are there, but it is all right. This is a sanctuary, and the animals act as if they know it. I have often thought it might be because of an invisible barrier, created by the fact that visitors are confined to the boardwalk, prevented from entering the animals' territory.
The animals do not stay back from the boardwalk, though. Barred owls sometimes sit dozing on the handrail, acknowledging passersby with what seems a bored blink. Limpkins and little blue herons probe among the sagittaria stalks so near that photographers complain they cannot get them in focus with their usual lenses. Courting red-bellied turtles carry on beneath the walk, and night herons with ruby eyes come to nap amid the Spanish moss curtaining the overhanging maples.
Deep down, my husband feels this enchantment, too, though he won't admit it. Scientists are like that. Instead, he measures litterfall and decomposition, nutrient cycling rates and vegetation growth, trying to see how those 400-year-old cypress got there. And whether there is any way to grow them back where they have been cut. They were cut twenty years ago in a buffer zone along the south end of the sanctuary, land that National Audubon bought after it was logged. But this logged area is coming back as only a jungle of pop ash and maple and willow. Why? Are enough cypress seeds getting there? Carolina parakeets ate cypress seed; could they have been important seed carriers?
The problem with research is that every time you answer one question, you uncover a dozen more you never had thought about. And some scientists get intrigued with tinier and tinier puzzles and spend a lifetime on esoteric, low-priority studies. Not that basic research is a waste of time; we often find that what seemed an insignificant academic problem is actually the key to a puzzling critical issue. But South Florida's problems are immediate. We need to reconcile delicate ecosystems and expanding population now. If we spend twenty years answering all the questions raised, it will be too late -- too late for corkscrew and for South Florida, too.
One the other hand, if time is not taken to examine that basic ecological mechanisms like evapotranspiration and nutrient cycling, even the most expensive environmental studies can do little more than state problems and offer educated guesses. Now we have an ecological overview of Corkscrew Swamp, and the question is: What else is really important to know?
Obviously, Corkscrew Swamp Sanctuary's fence lines follow legal property lines, not ecological boundaries. So in order to preserve Corkscrew, we need to look at the entire ecosystem -- the Big Cypress watershed -- and see that what is happening there does not disrupt the working of the natural systems that are critical to the continued health of our swamp, too.
But Audubon's responsibility does not end at looking out for our own. The habitats we have learned so much about by studying them at Corkscrew are not -- with the exception of the virgin cypress strand -- unique to our sanctuary. These exist all over South Florida, where people are worrying, too, about drainage and fire -- and logging, gracing, exotic species, offroad vehicles, highways, and airports. They want to know how much population the land can support and what sorts of developments the environment can tolerate.
We are now involved in further ecosystem studies, of the Big Cypress National Preserve and the Okefenokee Swamp.
If we find, as we expect, that comparable habitats function similarly throughout the region, then we can look at disturbed areas, and comparing measurements with data from the relatively undisturbed Corkscrew environment, determine just how much systems are changed by specific development or management practices.
Rather than rant and rave and forbid anyone to lay a finger on wild swampland, we will be able to make predictions in gallons and pounds per acre, which often can be expressed in terms of dollars. We will be in a position to state which proposed activities really threaten the Big Cypress ecosystem and to make constructive suggestions about alternatives. Then, when we see what patterns are consistent throughout southeastern wetlands, we can go to other swamps to try out our theories and begin to develop principles of swamp ecology that can be applied and used worldwide.