The island we visited is one of many research sites under study by the South Florida Water Management District, led by Director of Wetland Watershed Science, Dr. Fred Sklar. Since 1998 Dr. Sklar and his squad of ecologists have been monitoring nutrient deposition, plant communities and succession, and the ecology of wildlife on tree islands. Prior to Dr. Sklar’s work, very little was known about this distinctive and prominent feature of the Everglades landscape.
We asked Dr. Sklar to help us understand what SFWMD knows and how it is trying to address tree island ecology. A team of scientists and water management officials, including Assistant Executive Director Robert Brown, met us at mid-morning Thursday, and spent the early afternoon huddled with us under a canopy of cocoa plum and pond apple near the head of the island, explaining to us the patterns they are uncovering with their work.
Human manipulation of water flow has interrupted the processes by which tree islands grow and survive. Since 1940 the number of islands scattered throughout the Everglades has plummeted. In WCA-3, for example, tree island acreage is down from 24,800 acres to roughly 8100 acres, and the number of islands has fallen by almost 60%. Dr. Sklar told us things began going wrong in the 1940s, when lower levels of water in the central Everglades dissolved the layer of peat that develops on tree islands. In the 1960s we reversed course and began raising and maintaining high water in WCA-3, which is still destructive to tree islands. High water levels inundating the dry parts of tree islands eventually kill the species that grow in the “head,” the upstream end of the island where elevation is highest and the least water-tolerant trees grow. High water prevents the germination of seeds, leading to a loss of tree regeneration and preventing the growth of understory species and young trees that would otherwise replace older or damaged trees as they die off. Elsewhere, at the perimeters of the Everglades ecosystem canaling and water distribution have starved tree islands out of existence.
From an ecological standpoint tree islands are the anchors for wildlife in the Everglades. They provide roosting habitat for wading bird species, such as white ibis, tri-colored and little blue heron, snowy egret, white egret and great blue heron. They are a dry refuge for species of all kinds, from birds and small mammals to snakes, frogs, turtles and lizards. Whitetail deer are commonly found on tree islands. Even Florida panther and black bear have been documented on tree islands, far from their normal upland haunts. These islands are hubs of biodiversity in what is otherwise an inhospitable landscape for terrestrial wildlife. As the islands die out they become more spread out, making it harder for wildlife to travel from island to island. The proximity of the islands to each other is what enables all species to travel and reproduce.
Despite the grim prognosis, Dr. Sklar and his team of ecologists have a full plate of research ahead of them. As the the Everglades watershed changes through the back-filling and decompartmentalization projects introduced under the Comprehensive Everglades Restoration Plan (CERP) of 2000, SFWMD is in position to monitor the effects on tree islands and biodiversity. At this point there seems to be agreement that less water is needed in areas such as the one where our tree island was located, while many other areas have to be re-inundated in order to restore the processes that generate tree islands. Continued research is vital to our understanding of these unique islands.
As we rode back toward SR 41 on our visitors airboats the first rain of the expedition began to fall. It was a short sprinkle, but it punctuated the end of our ten days in this water-bound wilderness. I was energized by the new knowledge absorbed, and by the commitment of the scientists to make sure we finally get the water right in the Everglades.
For some mediocre pics of Everglades wading birds check out my Flickr!