Tropical hardwood hammocks are closed canopy forests, dominated by a diverse assemblage of evergreen and semi-deciduous tree and shrub species, mostly of West Indian origin. Tropical hardwood hammocks are found in South Florida or the Everglades, with large concentrations on the Miami Rock Ridge, in the Florida Keys, along the northern shores of Florida Bay, and in the Pinecrest region of the Big Cypress Swamp.
Tropical hardwood hammocks are habitat for a few endemic plants and are critical habitat for many West Indian plant species when the northernmost portions of their ranges extend into South Florida. Tropical hardwood hammocks also provide important habitat for many species of wildlife, including nine federally listed species. While the majority of the remaining hammocks outside of the Florida Keys have now been protected, hammocks are still significantly threatened by development in the Keys. Tropical hardwood hammocks have been heavily impacted by outright destruction, conversion to agriculture, exotic plant and animal species, collecting pressure on plants and animals, anthropogenic fires, and alterations in hydrology. Significant work has been initiated to restore existing disturbed tropical hardwood hammocks and to control exotic plant species. Numerous opportunities also exist to create or maintain tropical hardwood hammocks within the developed landscapes.
Distribution Large areas of tropical hardwood hammocks are found in Everglades National Park and Biscayne National Park, throughout the Florida Keys, and in Big Cypress National Preserve. Tropical hardwood hammocks also persist in small preserves along the Atlantic coastal strip from Miami-Dade County north to Martin County. Analogous communities are found in the Bahamas and the Greater Antilles.Robertson 1955 Most maritime hammocks on barrier islands in South Florida are similar to this community.
Description Tropical hardwood hammock is a closed canopy forest, dominated by a diverse assemblage of evergreen and semi-deciduous tree and shrub species, mostly of West Indian origin. It is important habitat for ferns and orchids of West Indian origin. Tropical hardwood hammock is not a fire maintained community, although fire may burn into tropical hardwood hammocks under certain conditions. Soils in tropical hardwood hammocks are primarily composed of organic material which has accumulated directly on top of mineral substrate, and are moist but rarely inundated.
Five major types of hammocks are: Rockland hammock "islands" on limestone substrate in or on the edges of pine rockland or marl prairie communities on the Miami Rock Ridge and in Big Cypress National Preserve. Keys rockland hammock on limestone substrate, making up the dominant forest type in the Florida Keys. Coastal berm hammock on storm-deposited berms in the Sand Keys (west of Key West), the Florida Keys, and along the northern shores of Florida Bay. Tree island hammock in the Everglades marsh and surrounding marl prairie. Shell mound hammock on aboriginal sites.
Tropical hardwood hammocks also include the more open coastal rock barren and sinkhole communities as classified by the Florida Natural Areas Inventory.FNAI and Florida Department of Natural Resources 1990 Coastal rock barren is a rare community occurring in tiny patches in the Florida Keys. Sinkholes are found in areas of karst limestone, primarily in hammocks on the Miami Rock Ridge.
Tropical hardwood hammocks are habitat for a few endemic vascular plants. While few plant species are endemic to tropical hardwood hammocks, hammocks are critical habitat for West Indian species where the northernmost portions of their ranges extend into South Florida. The canopy height of tropical hardwood hammocks varies according to substrate and climate. On the Miami Rock Ridge, a mature hammock will have a closed canopy at or less, while those on the Florida Keys have a canopy tall.Snyder et al. 1990 The tropical hardwood hammock shrub and herb layer is sparse, mostly consisting of seedlings and saplings of canopy and subcanopy trees and shrubs.
One of the most important ecotonal communities associated with tropical hardwood hammocks is the hammock edge where it interfaces with pine rockland, buttonwood wetlands, marl prairie, or other communities. The edges of hammocks are floristically very important, and many tropical hardwood hammock species are limited to these ecotones (although they may be found in other communities such as pine rocklands, or in hammock gaps following disturbance). Hammock gaps, similar to but substantially different from hammock edges, are also important to hammock dynamics. Historically, hammock gaps were created by storm events, including hurricanes, which allowed pioneer species to invade openings in the hammock canopy.
Coastal rock barrens are composed of two distinct subcommunities.Kruer 1992 Upland coastal rock barrens are openings on flat rocklands with sparse, mostly low-growing xeric plants and exposed limestone. Wetland coastal rock barrens are influenced by spring high tides and are dominated by common wetland plants and coastal shrubs.
Soils, hydrology, and climate Tropical hardwood hammock occurs on limestone, sand, and shell substrates which are moist and usually do not flood. Hammocks on limestone substrates, however, are dependent on the underlying water table to keep humidity levels high, especially in limestone sinkholes. Mesic conditions are developed by a combination of the hammock's rounded profile and nearly impenetrable edges, which deflect wind and limit the effects of desiccation. The dense canopy minimizes temperature fluctuations by reducing soil warming during the day and heat loss during the night.
Rockland hammocks are found on elevated outcrops of limestone, often in association with limestone sinkholes. Coastal berm hammocks are found on ridges of storm-deposited marine debris, usually within mangrove or salt marsh communities. In the Keys, these hammocks also occur fronting open water areas. Shell mound hammocks are found on elevated mounds of mollusk shells and aboriginal garbage on which a hardwood, closed canopy forest has developed. Coastal rock barrens are found on flat rocky surfaces either immediately adjacent to the coast or within the interior of islands in the Florida Keys. Sinkholes are cylindrical or conical depressions with steep limestone walls, found in karst rockland areas. Soils, when they exist, consist of calcareous marls and organic debris on the surface, within solution depressions, and in crevices in limestone.
Elevations on the Miami Rock Ridge vary from greater than above sea level in the vicinity of Biscayne Bay to less than above sea level in the Long Pine Key area of Everglades National Park, with an average elevation of approximately , and varying in width from .Davis 1943, USDA 1947, DERM 1995 Elevations of the limestone formations in the Keys are significantly lower, from 1 to above sea level. However, high elevations of above sea level are found in Key West and Lignumvitae Key.Snyder et al. 1990
Rainfall in southeastern Florida averages from over annually in the northwest portion of Miami-Dade County to between annually in the rest of the county. Mean rainfall in the upper Florida Keys is , and in the lower Keys is about . The majority of this precipitation (75 percent) occurs between June and October. Rainfall generally percolates quickly through the soil, maintaining fresh water or low salinity "lenses" below many hammocks.
Flora and fauna Flora Tropical hardwood hammocks are dominated by species of tropical origin, many of which are limited in their U.S. distribution to hammocks in the Florida Keys. While some West Indian species are relatively common in South Florida (e.g., gumbo limbo and strangler fig), many of these species are extremely rare and are listed as threatened or endangered by the State of Florida. Miami Rock Ridge hammocks are also important habitat for a number of listed epiphytic orchids, bromeliads, ferns, and peperomias found in the Big Cypress and other regions.
Trees
Buccaneer palm (Pseudophoenix sargentii) Canella (Canella winterana) Crabwood (Gymnanthes lucida) Cuban Nakedwood (Colubrina cubensis) Cupania (Cupania glabra) Darlingplum (Reynosia septentrionalis) Florida thatch palm (Thrinax radiata) Gulf licaria (Licaria triandra) Gumbo-limbo (Bursera simaruba) Hackberry (Celtis laevigata) Holywood lignum-vitae (Guaiacum sanctum) Jamaican dogwood (Piscidia piscipula) Krug's holly (Ilex krugiana) Live oak (Quercus virginiana) Manchineel (Hippomane mancinella) Milkbark (Drypetes diversifolia)
Paradise tree (Simarouba glauca) Pigeon plum (Coccoloba diversifolia) Princewood (Exostema caribaea) Pond apple (Annona glabra) Red mulberry (Morus rubra) Red stopper (Eugenia rhombea) Short-leaf fig (Ficus citrifolia) Soapberry (Sapindus saponaria) Soldierwood (Colubrina elliptica) Strangler fig (Ficus aurea) Torchwood (Amyris elemifera) West Indian mahogany (Swietenia mahagoni) Wild lime (Zanthoxylum fagara) Wild mastic (Sideroxylon foetidissimum) Wild tamarind (Lysiloma latisiliquum) Willow bustic (Sideroxylon salicifolium) Yellowheart (Zanthoxylum flavum)
Shrubs
Bahama strongback (Bourreria succulenta) Bay cedar (Suriana maritima) Beeftree (Guapira discolor) Bitterbush (Picramnia pentandra) Blackbead (Pithecellobium keyense) Black ironwood (Krugiodendron ferreum) Buttonwood (Conocarpus erectus) Cape Sable thoroughwort (Chromolaena frustrata) Cinnecord (Acacia choriophylla) Cocoplum (Chrysobalanus icaco) Coontie (Zamia integrifolia) Coralbean (Erythrina herbacea) Costa Rican ladies-tresses (Spiranthes costaricensis) Cuban colubrina (Colubrina cubensis) Firebush (Hamelia patens) Florida boxwood (Schaefferia frutescens) Florida trema (Trema micrantha) Hammock lantana (Lantana canescens) Inkwood (Hypelate trifoliata) Jamaica caper (Capparis cynophallophora) Keys hopbush (Dodonaea elaeagnoides) Lancewood (Ocotea coriacea) Limber caper (Capparis flexuosa)
Maidenbush (Heterosavia bahamensis) Marlberry (Ardisia escallonoides) Mayten (Maytenus phyllanthoides) Mexican alvaradoa (Alvaradoa amorphoides) Myrsine (Myrsine cubana) Myrtle-of-the-river (Calyptranthes zuzygium) Poisonwood (Metopium toxiferum) Potatowood (Solanum erianthum) Rough strongback (Bourreria radula) Rough velvetseed (Guettarda scabra) Satinleaf (Chrysophyllum oliviforme) Saffron plum (Sideroxylon celastrinum) Seashore ageratum (Ageratum littorale) Shrub eupatorium (Koanophyllon villosum) Spanish stopper (Eugenia foetida) Spicewood (Calyptranthes pallens) West Indies cherry (Prunus myrtifolia) West Indies lilac (Tetrazygia bicolor) White indigoberry (Randia aculeata) Wild coffee (Psychotria nervosa) White stopper (Eugenia axillaris) Wild dilly (Manilkara jaimiqui)
Plants and flowers
American beautyberry (Callicarpa americana) Ames' halbard fern (Tectaria × amesiana) Baby rubber plant (Peperomia obtusifolia) Bahama tree cactus (Pilosocereus bahamensis) Ballmoss (Tillandsia recurvata) Bamboo grass (Lasciasis divaricata) Barbwire cactus (Acanthocereus tetragonus) Biscayne spleenwort (Asplenium × biscayneanum) Blodgett's wild-mercury (Argythamnia bodgettii) Blue porterweed (Stachytarpheta jamaicensis) Boston fern (Nephrolepis exaltata) Brittle maidenhair fern (Adiantum tenerum) Broad halberd fern (Tectaria heracleifolia) Cape Sable thoroughwort (Chromolaena frustrata) Common nightshade (Solanum americanum) Costa Rican ladies tresses (Spiranthes costaricensis) Creeping fern (Thelypteris reptans) Cupania (Cupania glabra) False leadplant (Dalea carthagenense var. floridana) Florida dancinglady orchid (Oncidium floridanum) Florida filmy fern (Trichomanes punctatum ssp. floridanum) Florida govenia (Govenia floridana) - extinct Holly fern (Lomariopsis kunzeana) Least halberd fern (Tectaria fimbriata)
Florida oncidium (Oncidium floridanum) Giant airplant (Tillandsia fasciculata) Greenbrier (Smilax auriculata)