AN INTRODUCTION TO FLORIDA SCRUB
Welcome to Discovering Florida Scrub curriculum. Sorry the habitat name is not more inspiring. If Florida habitats could be named all over again, maybe scrub could be the Florida Dwarf Forest, or the Florida Elfin Woods, or the Florida Pygmy Oak Woodlands. Alas, it is too late now to choose a pretty name. Florida scrub is the original name, the tough name, the name that makes no promises. Maybe its an appropriate and meaningful name after all.
In spite of its unattractive name, Florida scrub is famous, recognized nationally as an unusual place with strange plants and animals. Biologists come from all over the country to study scrub. What is scrub and what makes it so special?
Florida scrub is frequently considered to be Floridas most distinctive ecosystem. With so many interesting ecosystems that exist in Florida, such as mangrove swamps, hardwood hammocks, dry prairies, and freshwater marshes, the title is an honorable one. Florida scrub has some very striking differences.
Florida scrub is a very old ecosystem found on coastal and ancient inland dunes throughout the state. Some of the inland ridges of scrub have been around since the early Pleistocene (approximately one million years ago), while other parts of Florida, such as the Keys, have been above sea level for only a few thousand years.
While much of Florida is very flat, low, and wet, Florida scrub is relatively high (sometimes more than 200 feet above sea level), dry, and desert-like. Although seventy-six percent of the annual rainfall (or approximately 40 inches) is produced during six months of summer, winters are very dry. Rain drains through scrub soil very quickly. Even within an hour of a heavy rain, very little water will remain on top of the sand. (During the wet season, seasonal ponds may form in some depressions found among the ridges.)
Most of Florida is sandy. But while many habitats have rich organic matter mixed with sand, scrub soils have lost almost all of their organic components to the action of wind, waves, and water and are chronically low in nutrients. Because water soluble compounds leach out quickly, only plants adapted to the dry, sandy soil and low nutrient levels can survive.
Fire affects almost all plant communities in Florida, but the frequency of fire in scrub is higher than for other habitats. Fires usually occur at intervals of about 5-25 years in scrub. Lightning strikes central Florida more frequently than anywhere else in the United States. Historically, lightning-ignited wild fires periodically scorched, yet regenerated, patches of the scrub landscape. These regularly occurring fires swept across the landscape in erratic patterns, keeping scrub relatively low and open and ensuring a mosaic of scrub that varied in stages of growth.
More than anything else, plants define Florida scrub. (Biologists typically define habitats by the community of plants that are found in an area. Sixty-nine different plant community types occur in Florida.) Florida scrub has a very distinct plant community. Instead of the trees or grasses found in many other Florida habitats, scrub is dominated by shrubs and dwarf oak trees, with an occasional pine mixed in. Other plants typically found in scrub include low palmettos, hickories, and Florida rosemary. Scattered throughout the scrub are bright, open patches of bare sand dotted with small herbaceous plants and lichens.
The combination of plants that occur in scrub varies from site to site. Sand pine scrub is sometimes open and airy or forest-like with a dense overstory of mature sand pines and a shrub layer underneath. On more excessively drained scrub sites you may find nearly pure stands of Florida rosemary. Oak scrub can be dense or open. Coastal scrub can be treeless. Some of the shrubs, small plants, and trees that live in Florida scrub occur nowhere else in the world.
Living among the plants are many animalsmammals, birds, reptiles, amphibians, insects, and spiders. Among these organisms are forty species of plants, four species of vertebrates, and at least forty-six species of arthropods that are found in Florida scrub and nowhere else. These species are well adapted to life in the dry, sandy, nutrient-poor scrub soil.
Florida scrub is found on coastal and inland ridges throughout Florida. These ridges also support other dry, but very different habitats, such as sandhill and scrubby flatwoods.
As seen on the map, three major groupings of scrub exist: coastal panhandle, coastal peninsula, and inland peninsula. The biggest areas of scrub are found inland with the largest block occurring in and around Ocala National Forest.
Millions of years ago, these ridges were formed by rising and falling sea levels. During the periods when the sea level was high and flooded most of peninsular Florida, these ancient islands became refuges for plants and animals. Populations were isolated from the mainland for thousands of years and evolved within these small, sandy habitats. The central inland ridges are older, having remained islands while coastal ridges were flooded, and have a greater concentration of endemic species.
The Lake Wales Ridge, an inland ridge, is the highest and oldest ridge in Florida. Extending about 100 miles north to south from Clermont to Venus and 4 to 10 miles wide, the Lake Wales Ridge holds a large portion of the remaining scrub habitat. Several scrub species--17 species of plants, 1 species of vertebrates, and at least 10 species of arthropods--are found on the Lake Wales Ridge and on no other ridges. (For a list of these species, contact the Florida Fish and Wildlife Conservation Commission.)
Before the ridges were formed when the southeastern United States was very dry, many western species were also found in Florida. When the climate became much wetter, some of these desert species were able to survive on the dry sandy ridges. When the oceans receded, these species remained on the ridges. Today, these species, such as the gopher tortoise, the Florida mouse, and the Florida scrub-jay, have obvious western relatives, but are really quite different.
For more information about scrub sites in your area that are accessible to the public, contact the Florida Fish and Wildlife Conservation Commission, the U.S. Fish and Wildlife Service, The Nature Conservancy, or your water management district office.
Why do so many plant and animal species live only in Florida scrub?
The reason: this habitat has an unusual blend of challenges and opportunities, and some plants and animals are specialized to meet these challenges and take advantage of these opportunities. Life in Florida scrub is complicated, as it is everywhere else. However, the combination of scrubs distinctive features and history make it exceptional:
First, sand is ideal for animals that dig. Many of these animals require deep, well-drained soil or are dependent on hosts that, in turn, depend on the characteristics of scrub soil. While sand provides opportunities for digging animals, their natural enemies also move easily through sand and are a constant threat.
Second, while fires are a hazard for scrub plants and animals, they also provide opportunities for a new start in less crowded conditions. Most scrub plants are adapted to fire and can resprout or reseed. The sand can act as a bank, storing viable seeds, sometimes for decades, until the conditions are right for germination. Sometimes seeds only need an open area where sun can warm the sand.
Third, as mentioned above, some of the species found in Florida scrub are related to western species that were also found here. Florida scrub is a lingering example of a series of dry habitats that extended from southwest North America across southern North America to Florida hundreds of thousands of years ago. Since Florida is often very hot and dry and has very porous soil, some plants and animals from the old dry habitat have remained in scrub---even though the climate is now much wetter.
What plants and animals are found in scrub?
Because of scrubs unusual blend of features, Florida scrub has unique and fascinating species, including the Florida scrub-jay, the Florida mouse, the sand skink, the blue-tailed mole skink, the various species of scrub mints, the Highlands scrub St. Johns-wort, the scrub golden aster, and the scrub wedge-leaf button snakeroot. All of these species are considered either threatened or endangered. They are rare because they have a limited distribution within Florida scrub and may occur at some scrub sites but not others. They are also rare because much of their habitat has recently been destroyed for agriculture, commerce, and housing. Many other scrub species, such as the Florida scrub lizard and the scrub pawpaw, are not in trouble yet, but the areas where they live and grow are also diminishing.
The Florida scrub-jay is probably the best-known scrub endemic. Scrub-jays require a low shrub layer with no canopy. When fires are suppressed, scrub becomes overgrown and scrub-jays abandon the site. Eighty-five to ninety percent of the Lake Wales Ridge xeric uplands, which include scrub, have been lost to development or agriculture. Much of the remaining ten percent is degraded or has been subdivided for residential use. Proper management of the remaining scrub can be difficult or sometimes impossible.
Mourning over the losses with your students, most likely, will not help them foster a positive attitude toward threatened habitats. Students need opportunities to discover and celebrate what remains and to find the personal value of wild places as well as the biological necessity of them. These students could grow up to be guardians of our Florida scrub heritage.