South Florida Pine Rockland

This system includes pinelands of extreme south Florida growing on limestone. The uniqueness of the flora associated with this type has long been recognized, including the number of endemic and West Indian species. Many plant and animal taxa found in this system are restricted to it, including many of south Florida's endemic plants. Unlike pinelands elsewhere in the southeastern coastal plain, Pinus elliottii var. densa is the only native pine species in this system. Understory vegetation consists of many hardwood species, including a number with tropical origins, and the herbaceous flora is species-rich and fire-adapted.

Pinus elliottii var. densa is the only native pine species in this system. Stands have an open canopy, generally with multiple age classes. It has been estimated that nearly one-third of the taxa found in this system are restricted to it, including half of south Florida's endemic plants (Stout and Marion 1993). The diverse, open shrub/subcanopy layer is composed of more than 100 species of palms and hardwoods (Gann et al. 2009), most derived from the tropical flora of the West Indies (Snyder et al. 1990). Many of these species vary in height depending on fire frequency, getting taller with time since fire. These include Ardisia escallonoides, Byrsonima lucida, Coccothrinax argentata, Dodonaea viscosa, Guettarda scabra, Metopium toxiferum, Morella cerifera (= Myrica cerifera), Myrsine cubana (= Rapanea punctata), Psidium longipes, Rhus copallinum, Sabal palmetto, Serenoa repens, Sideroxylon salicifolium, Tetrazygia bicolor, and Leucothrinax morrisii (= Thrinax morrisii). Short-statured shrubs include Chiococca alba, Crossopetalum ilicifolium, Morinda royoc, and Randia aculeata. Grasses, forbs, and ferns make up a diverse herbaceous layer ranging from mostly continuous in areas with more soil development and little exposed rock to sparse where more extensive outcroppings of rock occur. Typical herbaceous species include Andropogon gracilis (= Schizachyrium gracile), Andropogon spp., Anemia adiantifolia, Aristida purpurascens, Chamaecrista fasciculata, Chamaesyce spp., Croton cascarilla (= Croton linearis), Echites umbellatus, Muhlenbergia capillaris, Pteridium caudatum (= Pteridium aquilinum var. caudatum), Pteris bahamensis, Rhynchospora floridensis, Schizachyrium rhizomatum, Schizachyrium sanguineum, Sorghastrum secundum, Tragia saxicola, and Zamia pumila. The range of this system is largely outside the natural range of Pinus serotina, Pinus elliottii var. elliottii, and Pinus palustris.

Pine rockland occurs on relatively flat, moderately to well-drained terrain from 2-7 m above sea level (Snyder et al. 1990). Along the southeastern coast of Florida this system occurs on Miami Oolitic Limestone, while in the Big Cypress region (southwest Florida) it is found on outcrops of Tamiami Limestone. Outcrops of weathered oolitic limestone, known locally as pinnacle rock, are common, and solution holes may be present (FNAI 2010a). The oolitic limestone is at or very near the surface, and there is very little soil development. Soils are generally composed of small accumulations of nutrient-poor sand, marl, clayey loam, and organic debris in depressions and crevices in the rock surface. Organic acids occasionally dissolve the surface limestone causing collapsed depressions in the surface rock called solution holes (Outcalt 1997b). Drainage varies according to the porosity of the limestone substrate, but is generally rapid. Consequently, most sites are wet for only short periods following heavy rains. During the rainy season, however, some sites may be shallowly inundated by slow-flowing surface water for up to 60 days each year.

Historical accounts show that fire has been frequent over the past several hundred years, perhaps as often as every 1-4 years (Wade et al. 1980, Bergh and Wisby 1996, Slocum et al. 2003). Without fire, after 15-20 years, hardwoods will be numerous and quite large (Wade et al. 1980). In the absence of fire, this system may be replaced by hardwoods species within several decades (Stout and Marion 1993). High winds from hurricanes are an infrequent, natural disturbance. Pine rockland in the Florida Keys can be subjected to storm surge associated with hurricanes (Saha et al. 2011).

Fragmentation is a threat, especially in the Miami area. Lack of fire is a threat, which allows the encroachment of hardwood trees. Invasive exotic plants are also a threat, such as Melinis repens, Neyraudia reynaudiana, and Schinus terebinthifolius (Landfire 2007a, FNAI 2010a). Habitat loss due to development pressure is a threat to remaining pine rockland on private lands, such as in the Florida Keys. Storm surge associated with hurricanes is a threat to pine rockland areas at less than 2 m elevation (Saha et al. 2011).

Davis (1943) mapped this system, which occurred primarily on the Miami ridge bordering the Everglades, with disjunct examples found in the Big Cypress Swamp. Davis estimated there once was 180,000 acres of "Miami region pine" (Davis 1943). McPherson's (1986) map of Big Cypress shows "pine forest," which includes both pine rocklands and pine flatwoods, scattered across the unit. It may be possible to differentiate based on soil type or geology, the pine rockland being in the southeast part of Big Cypress. In the Florida Keys it is found on Big Pine Key, No Name Key, Little Pine Key, Cudjoe Key, and Upper Sugarloaf Key. The Miami Rockridge extends from around downtown Miami southwest to Long Pine Key in Everglades National Park (Miami-Dade County). Big Pine Key is in Monroe County, and the Big Cypress National Preserve is in Monroe and Collier counties. In addition, pine rockland historically occurred in the upper Florida Keys; pine stumps and remnant species characteristic of pine rockland have been found in one area of Key Largo (Alexander 1953). There has been an estimated 98% decline in the amount of pine rockland habitat on the Miami Rock Ridge in southern Florida, outside of the Everglades National Park where Long Pine Key is protected (Noss et al. 1995, Enge et al. 2002). About 6200 ha (15,000 acres) of pine rockland remain (Enge et al. 2002).