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CENTRAL HIGHLANDS OF FLORIDA
The Central Highlands Region of peninsular Florida consists of a series of rather localized high grounds, comprising near parallel north-south ridges that are remnants of beach and sand-dune systems associated with Miocene, Pliocene or Early Pleistocene shorelines. The region consists of xeric residual sandhills, beach ridges and dune fields, the whole of which is interspersed with numerous sinkhole lakes and basins caused by erosion of the underlying limestone bedrock. The main axis of the Central Highlands is the Central Ridge, extending from south-eastern Lake County in the north to southern Highlands County in the south. This comprises the Lake Wales Ridge, Winter Haven Ridge, Lake Henry Ridge and Bombing Range Ridge. This is the oldest of the ridge systems. An outlying ridge system to the north-west and extending from Gilchrist County to Polk County comprises the Bell Ridge, Brooksville Ridge, Cotton Plant Ridge and Lakeland Ridge. Slightly to the north-east and ranging from Marion and Putnam counties south to Osceola County are the Mount Dora Ridge, Crescent City Ridge, DeLand Ridge and Orlando Ridge. To the north and extending to the Georgia border is the Trail Ridge (Map 7). To the far east, beginning in the south-eastern tip of Duval County and extending southward along the coast is the Atlantic Coastal Ridge. The latter, the youngest of the ridge systems, is not included as part of the Central Highlands, although it does have some phytogeographic affinities with the Central Highlands. These ridge systems rise above the Polk, Lane, Sumter and Marion Uplands, which have less relief. The general area also encloses large lowlands - the Central and Western Valleys, and the St Johns River Valley. The Lake Wales Ridge, one of the most prominent physiographic features of peninsular Florida, is only a few kilometres wide but more than 150 km long.
The predominant vegetation of the xeric uplands is scrub, consisting of sand pine (Pinus clausa) and sclerophyllous oaks (Quercus inopina, Q. geminata, Q. chapmanii, Q. myrtifolia). Along a hydrological gradient, scrubs vary from low scrubs, also called scrubby flatwoods, which are dominated by Serenoa repens, Quercus spp., Lyonia spp. and Ilex glabra, to very xeric rosemary balds dominated by Ceratiola ericoides. Interspersed is the sandhill or wiregrass community and the more xeric turkey oak barrens, the latter dominated by Quercus laevis. In the lowlands are numerous wet swales, ponds and lakes, which are often of sinkhole origin. Natural or anthropogenic fires help maintain these xeric uplands.
Florida has more federally listed endangered and threatened species than any state east of the Mississippi River. Thirty-eight plant species occurring in Florida are listed with the U.S. Fish and Wildlife Service (USFWS). Of these, 16 occur in the Central Highlands Region (Table 20). Nowhere else in the state is there a higher concentration of federally endangered or threatened plant taxa.
The Central Highlands has a high number of endemic or near endemic (>90% of range in Florida) species, a large majority occurring in the scrub habitat. The Central Ridge has 27 families containing endemic species. It is also the centre of speciation for woody species of Dicerandra (Lamiaceae). Forty-three species have their centre of distribution in the Central Ridge Region (Table 21).
Within the last ten years, five species of plants new to science have been described from the Central Highlands Region: Conradina etonia (Kral and McCartney 1991), Crotalaria avonensis (DeLaney and Wunderlin 1989), Dicerandra christmanii (Huck et al. 1989), Lupinus aridorum (Beckner 1982), and Ziziphus celata (DeLaney, Wunderlin and Hansen 1989). Three of these (Crotalaria, Dicerandra and Ziziphus) are restricted to the Lake Wales Ridge.
Christman (1988) considers 114 plant species to be characteristic of scrubs in peninsular Florida. A further 202 plant species are known to occur at least occasionally in peninsular Florida scrubs. There are 41 vascular plant species restricted to the Central Highlands scrubs, of which 19 are restricted to the Central Ridge Region.
Although most of peninsular Florida was inundated in the past, particularly during the Pliocene and Pleistocene interglacial periods, the southern portion of the Lake Wales Ridge has apparently been emergent and suitable for plant habitation since the Late Miocene or the Early Pliocene (Huck et al. 1989). It is probable that the Lake Wales Ridge served as a refugium for plants during times of higher sea-levels. An equally important factor in the development of high endemism are the deep, dry, sandy soils of the palaeo-dune fields and ridges of the Lake Wales Ridge. A large number of taxa have become adapted to this xeric environment. More recently, other ridge systems in the Central Highlands apparently served a similar role.
The endemic plant species of the Central Highlands are undoubtedly of various origins and ages (Huck et al. 1989). Many appear to be neoendemics that share a recent common ancestor or are derived from a wide ranging eastern North American taxon (e.g. Osmanthus megacarpus, O. americanus, Chionanthus pygmaeus, C. virginicus), while others appear to have a south-western affinity (e.g. Bonamia grandiflora, Carya floridana, Liatris ohlingerae, Palafoxia feayi, Ziziphus celata). There is little, if any, Caribbean influence in the region.
Although a precise inventory of plant species has never been completed for any of the ridges, species diversity is high. For example, the Archbold Biological Station, a 1590 ha preserve located at the southern end of the Lake Wales Ridge and with excellent examples of scrub vegetation, contains 535 species of vascular plants (Abrahamson et al. 1984).
Although little is known of economically important plant species other than a few timber and food plants, several scientists are currently investigating the natural chemical defences of scrub plants for compounds which may prove useful as insecticides, insect repellents (Eisner et al. 1990; Eisner 1994) or herbicides. One example is Diceranda frutescens, an endangered species found in the Archbold Biological Station, which contains trans- pulegol, a potent insect repellent (Eisner 1994).
The many lakes and white sandy beaches, often bordered by citrus groves, are highly attractive for residential and recreational development. The unique habitat and geological history also contribute to high endemism in the fauna. Three species of vertebrates with distributions largely in the Central Highlands are listed by the USFWS as threatened. Arthropods endemic to the Florida scrub habitat are concentrated on the Lake Wales Ridge (Deyrup 1990).
The deep sands, highly favoured for citrus cultivation, have resulted in the Central Highlands Region being a major citrus producing region in the state, a $1.4 billion industry.
Like many other parts of Florida, the Central Highlands is undergoing rapid and intense development. The major threat to the Central Highlands natural environment is conversion of scrub habitat to citrus groves. Other major threats are conversion to residential, commercial and recreational uses. About 80% of the upland habitats on the southern Lake Wales Ridge have been converted to citrus groves or residential developments (Peroni and Abrahamson 1985a, 1985b). Although no data are currently available, similar amounts of conversion are expected for other areas of the Central Highlands. Of major impact is Walt Disney World and its satellite developments of hotels, restaurants, homes and other theme parks on the Orlando and Mount Dora ridges. Some property owners faced with existing or pending developmental restrictions if their property is found to contain endangered or threatened plant or animal species have wilfully destroyed scrub habitat before proper plant and animal surveys could be conducted.
Because of the high level of endemism in the Central Highlands Region, considerable interest has been generated by environmentalists in preserving this fragile habitat and its flora. Recovery plans are completed for all 13 plant species occurring on the Central Ridge that are listed by the USFWS as endangered or threatened species.
Several natural area preserves on the Central Ridge provide protection for some state endemics (Christman and Judd 1990). The Archbold Biological Station in southern Highlands County protects about 315 ha of scrub and 13 endemic species (Abrahamson et al. 1984). The Nature Conservancy's (TNC) Saddle Blanket Lakes Preservation covers about 30 ha in Polk County and offers protection for 11 plant species. The proposed Lake Arbuckle State Park will include about 300 ha and 10 plant species. The TNC Tiger Creek Preserve does not contain any true scrub, but does have natural turkey oak barrens with five endemic plant species. At Catfish Creek in Polk County, TNC has recently acquired about 120 ha, including scrub with five endemic plant species. Two endemics are protected at Highlands Hammock State Park. Two or three endemic plant species are protected at Turkey Lake, Lake Cain and Lake Marsha parks, and several small parks in Orange County. Four species of Central Ridge endemics are not protected anywhere, and 12 have fewer than five protected populations.
A conference "Biological Priorities for a Network of Scrub Preserves on the Lake Wales Ridge" was held at the Archbold Biological Station, 29-30 November 1989. As a result, there is now an active programme at the local, state and national level to preserve scrub habitat on the Lake Wales Ridge. Nearly 13,000 ha of scrub habitat have been proposed for purchase by the State through its 1992 Conservation and Recreational Lands (CARL) programme, which is part of the ten year $3 billion Preservation 2000 programme. Efforts are also underway by the USFWS to establish the first U.S. refuge specifically for endangered plant species.
Through the state's wetland protection laws, three endemic plant species of wetland habitats are protected on the Central Ridge. They are Hartwrightia floridana, Hypericum edisonianum and Panicum abscissum.
Bok Tower Gardens, Lake Wales, operating under the National Collection of Endangered Plants programme of the Center for Plant Conservation (CPC), maintains a living collection of 19 species of Central Highlands plants.
Map 7. Central Highlands of Florida, U.S.A. (CPD Site NA29)
Abrahamson, W.G., Johnson, A.F., Layne, J.N. and Peroni, P.A. (1984). Vegetation of the Archbold Biological Station, Florida: an example of the southern Lake Wales Ridge. Florida Scientist 47: 209-250.
Beckner, J. (1982). Lupinus aridorum J.B. McFarlin ex Beckner (Fabaceae), a new species from central Florida. Phytologia 50(3): 209-211.
Christman, S.P. (1988). Endemism and Florida's interior scrub. Final Report to Florida Game and Fresh Water Fish Commission. Tallahassee. Contract No. GFC-84-101. 247 pp.
Christman, S.P. and Judd, W.S. (1990). Notes on plants endemic to Florida scrub. Florida Scientist 53: 52-73.
DeLaney, K.R. and Wunderlin, R.P. (1989). A new species of Crotalaria (Fabaceae) from the Florida Central Ridge. Sida 13(3): 315-324.
DeLaney, K.R., Wunderlin, R.P. and Hansen, B.F. (1989). Rediscovery of Ziziphus celata (Rhamnaceae). Sida 13(3): 325-330.
Deyrup, M. (1990). Arthropod footprints in the sands of time. Florida Entomologist 73: 529-538.
Eisner, T. (1994). Chemical prospecting: a global imperative. Proceedings of the American Philosophical Society 148(3): 385-393.
Eisner, T., McCormick, K.D., Sakaino, M., Eisner, M., Smedley, S.R., Aneshansley, D.J., Deyrup, M., Myers, R.L. and Meinwald, J. (1990). Chemical defense of a rare mint plant. Chemoecology 1: 30-37.
Florida Natural Areas Inventory (1990). Matrix of habitats and distribution by county of rare/endangered species in Florida. Tallahassee.
Huck, R.B., Judd, W.S., Whitten, W.M., Skean, J.D., Wunderlin, R.P. and DeLaney, K.R. (1989). A new Dicerandra (Labiatae) from the Lake Wales Ridge of Florida, with a cladistic analysis and discussion of endemism. Syst. Bot. 14: 197-213.
Kral, R. and McCartney, R.B. (1991). A new species of Conradina (Lamiaceae) from northeastern peninsular Florida. Sida 14(3): 391-398.
Myers, R.L. and Ewel, J.J. (eds) (1990). Ecosystems of Florida. University of Central Florida Press, Orlando. 765 pp.
Peroni, P.A. and Abrahamson, W.G. (1985a). Vegetation loss on the southern Lake Wales Ridge. Palmetto 5: 6-7.
Peroni, P.A. and Abrahamson, W.G. (1985b). A rapid method for determining loss of native vegetation. Natural Areas J. 5: 20-24.
White, W.A. (1970). The geomorphology of the Florida peninsula. Geological Bull. 51. Bureau of Geology, Florida Department of Natural Resources, Tallahassee. 164 pp.
Wunderlin, R.P. (1982). Guide to the vascular plants of Central Florida. University of South Florida Press, Tampa. 472 pp.
Zona, S. and Judd, W.S. (1986). Sabal etonia (Palmae): systematics, distribution, ecology and comparisons to other Florida scrub endemics. Sida 11(4): 417-427.
This Data Sheet was written by Richard P. Wunderlin (Department of Biology, University
of South Florida, Tampa, FL 33620-5150, U.S.A.).
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