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By Cathy Vogelsong Reprinted from The Understory, Aug.-Sep. 2003  Pine flatwoods are the most extensive terrestrial ecosystem in Florida, distributed over 50% of the state's land area, and north into neighboring states, ranging in climate from subtropical to warm temperate. However, the most important climate factor is not temperature, but the seasonal change in precipitation. Flatwoods have, as the name implies, a low, flat topography, but because of this and generally poor drainage, small differences in elevation result in major vegetation changes. The pine flatwoods -- typically dotted with cypress domes, cabbage palm flatwoods, marshes, and other habitats -- is the matrix that ties many other Florida ecosystems together. Pine flatwoods have a very stratified appearance, with a high canopy of pines, a low shrubby layer, and an herbaceous layer. The canopy density varies considerably but is always "discontinuous," allowing a great amount of light to penetrate to the herbaceous ground cover (and preventing canopy fires). Habitats in Florida are often classified as xeric (dry), mesic, and hydric (wet) and the distribution of the four dominant trees in flatwoods roughly correlates with this. The slow-growing longleaf pine (P palustris) dominates well-drained, frequently burned sites. The two slash pine varieties, faster-growing and less fire-tolerant than longleaf, occupy mesic sites. Typical slash pine (Pinus elliottii var. elliottii) is found in the north half of the state, and the south Florida slash pine (P. e. var. densa) is found in the south. Pond pine (P. serotina) is found in poorly drained, hydric systems, but only as far south as Orange County in mid-Florida. Now, with man's intervention, slash and longleaf pines often mix. Common shrubby understory plants include saw palmetto, gallberry, wax myrtle, low runner oaks and many species in the acid-loving Ericaceae family. The herbaceous ground cover, dominated by wiregrass, may be sparse, or it may be very diverse in sites with open canopies and shrub cover. Species diversity is also highest in mesic sites. Pine flatwoods have few endemic animal species compared to other ecosystems. Three large mammals, white-tail deer, black bear and Florida panther, use the flatwoods. Species of special concern include red-cockaded woodpecker, fox squirrel, and southeastern kestrel. Armadillo and wild hog are nuisance exotics. There are a variety of soil types in pine flatwoods, but they are generally poorly drained, sandy and acidic. These fine sands were originally laid down as deposits on shallow sea beds, when sea levels rose between periods of glaciation. Flatwoods soils are very low in available nutrients, clay, and organic material. (Note that conifers, especially pines, have lower nutrient requirements than hardwoods.) Flatwoods often have a clay hardpan. In the rainy season, hardpan soils can become waterlogged and poorly aerated, with standing water for varying periods in the hydric and mesic sites. During the dry season when evaporation dries out the surface soil, the impermeable hardpan can prevent lower water from rising, creating drought conditions for the plant life. The fluctuations in water table, and presence of a hardpan, can inhibit root growth. Because of these factors, there is tremendous seasonal variation in the amount of water available to the vegetation. The pine flatwoods ecosystem represents a succession subclimax, maintained by, and dependent upon, frequent fires. The frequency of fire keeps the litter and nutrients in the soil low and bums out encroaching oak seedlings. These fires spread fast, burning at a lower temperature. Where man has restricted fire, ecosystems have changed. In unburned flatwoods, soil moisture is higher because of accumulated litter, available nutrients increase, and plant succession progresses with hardwood tree species moving in. Then fires, when they do occur, will bum hotter with more devastating effect. Hardwood tree roots, unlike pine roots, can penetrate and break up the thin clay hardpan, altering the hydrology of the site. Pine flatwoods plants have developed many adaptations to fire and seasonal water conditions. These include great fire tolerance, and thick, small leathery leaves to decrease evaporation. Wiregrass and palmetto are highly flammable, which facilitates fire, Many plants have enlarged underground parts, allowing them to survive and regrow rapidly after fires. Some seeds require fire to germinate, a beneficial adaptation since increased nutrients in the soil following a bum. The timing of burns is also important. Lightning-started fires typically occur during the summer rainy season. Wiregrass requires spring/summer fires to flower, for example. Man has altered the pine flatwoods in many ways. At one point, the southeast U.S. longleaf and slash pinelands produced 75% of the world's gum naval stores -- rosin, turpentine, and other products produced from the gum/sap of pines. And all old growth longleaf pine was cut for timber. Flatwoods escaped most development and agricultural use until the 1950s when drainage and fertilizer technologies improved. Much flatwoods acreage is now managed for livestock and slash pine plantations (for pulpwood), drastically altering the associated plant communities. Prescribed bums are often done in winter (common on ranchland), or fire is suppressed altogether. Development has also destroyed or changed much habitat by suppressing fires, draining land, etc. Exotics, especially Brazilian pepper and melaleuca, invaded the moister flatwoods in south Florida. Besides the wide variety of conditions within the pine flatwoods, there are major recognizable variations. Myers and Ewel (Ecosystems of Florida), and Walter Kingsley Taylor (Florida Wildflowers and Their Natural Communities), both described dry prairie and scrubby flatwoods, with Taylor adding a third, cabbage palm flatwoods. The dry prairie is very similar to pine flatwoods but is treeless. The acidic soils support a great variety of wildflowers. Like pine flatwoods, the dry prairie is a mosaic of habitats. Examples are found at Kissimmee Prairie, Myakka River State Park, and areas north and west of Lake Okeechobee. The scrubby flatwoods may be an ecotone, with a combination of pine flatwoods and scrub characteristics. However, the scrubby flatwoods are notable for the absence of fire, and a characteristic species, scrub oak (Q. inopina), is rare in true flatwoods and scrub. Scrubby flatwoods are found on well-drained white sand. There is never standing water, but the water table itself is higher than in a true scrub. It has a very open canopy and a sparse herbaceous layer. The shrubby understory is dominated by shrub oak species, saw and scrub palmetto, and wiregrass. The cabbage palm flatwoods has a canopy of cabbage palms, with or without pond or slash pine, and the palms may be quite dense. As with the dry prairie, fire is necessary. The sandy soil overlays an alkaline material such as shell or marl, so it has a much higher pH (6.0 to 7.5) than the other flatwoods types. Examples are found on Merritt Island and Tosohatchee State Reserve. References: Ecosystems of Florida, Ronald Myers and John Jewel, editors, Univ. Press of Florida, 1990. Florida Wildflowers in Their Natural Communities, Walter Kingsley Taylor, Univ. Press of Florida, 1998
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