Mesic Temperate Hammock
Mesic temperate hammocks are closed canopy forests, dominated by evergreen tree species of temperate affinities, primarily live oak and cabbage palms, that are naturally protected from fire because of their position in the landscape. Soils in mesic temperate hammocks remain moist due to shading and dense leaf litter, but they are rarely inundated. Mesic temperate hammocks are found primarily in four topographic positions in the South Florida Ecosystem: (1) as islands in a pine-cypress-or graminoid-dominated community, also known as prairie hammock (FNAI and FDNR 1990); (2) as islands on elevated areas within floodplain wetlands, (3) on levees of rivers, and (4) midslope or ecotonal between xeric communities and low-lying wetland communities. Mesic temperate hammock occurs as prairie hammock islands on slight elevations within the relatively flat terrain of central and South Florida (FNAI and FDNR 1990). In Okeechobee and Glades counties, they occur as islands in dry prairies composed of saw palmetto and graminoid species (FNAI 1995, Hilsenbeck and Hedges 1994). In Big Cypress National Preserve, at the southern extent of this community in Florida, hammocks develop on limestone outcroppings within graminoid marsh or open cypress forest (Snyder et al. 1990, Duever et al. 1979). Mesic temperate hammock islands also develop on elevated areas within hydric hammocks, as in the Upper Lakes Basin Watershed in Polk and Osceola counties (Bridges and Reese 1996). Mesic temperate hammock occurs in extensive bands along historical floodplain boundaries in the Kissimmee River Valley and also on elevated ridges and knolls within the floodplain (Milleson et al . 1980). It also exists as an ecotonal community, transitional between xeric uplands, such as scrub and high pine, and wetland communities such as hydric hammock, wet flatwoods, floodplain forest, or baygall. Examples of this hammock type occur at Highlands Hammock SP (P. Anderson, DEP, personal communication 1998) and Avon Park AFR (Orzell 1997). In each of these landscape positions, mesic temperate hammock occupies somewhat better drained soils than surrounding or adjacent wetland communities, although dense litter accumulation and a closed canopy maintain relatively high soil moisture conditions at most times.
Mesic temperate hammock is characterized in South Florida by a closed canopy of hardwood species, primarily live oak and cabbage palm, and by a fairly open shrub layer and a sparse, species-poor herb layer. Herb diversity is frequently higher among epiphytes than among ground layer species. Canopy tree dominants are relatively constant in mesic temperate hammocks throughout the South Florida Ecosystem. Live oak and cabbage palm are consistently present, and are joined by water oak (Quercus nigra), laurel oak (Q. laurifolia), hackberry (Celtis laevigata), red maple (Acer rubrum), and other temperate hardwoods at many sites. Hammocks at the northern boundary of the South Florida Ecosystem are more diverse and may contain species such as pignut hickory (Carya glabra), sweet gum (Liquidambar styraciflua), and southern magnolia (Magnolia grandiflora) that do not occur further south (Bridges and Reese 1996). Hammocks at the border of the tropical zone often contain tropical species such as strangler fig (Ficus aurea) and trema (Trema micrantha) (Austin et al. 1977, Cox 1988). Although canopy composition is relatively constant in mesic temperate hammock throughout its range in Florida, shrub species composition is variable across the range of this community within South Florida. A unifying factor is the presence of at least some shrub species considered tropical in even the most northern locations within the South Florida Ecosystem (Bridges and Reese 1996). Tropical shrub species found in hammocks throughout South Florida include wild coffee (Psychotria nervosa and P. sulzneri), marlberry (Ardisia escallonioides), and myrsine (Myrsine floridana). The dense, closed canopy of the hammock protects such tropical species from freezing temperatures. Observers of mesic temperate hammocks in South Florida have commented on the low species diversity of the herb layer, while simultaneously noting the abundance of epiphytes (Harshberger 1914, Harper 1927). Epiphytes include orchids (Encyclia tampensis, Epidendrum conopseum, E. anceps, Harrisella filiformis), ferns (Vittaria lineata, Polypodium polypodioides, Phlebodium aureum, Cheiroglossa palmata), and bromeliads (Tillandsia setacea, T. utriculata, T. usneoides, T. fasciculata, and T. flexuosa).
Because mesic temperate hammocks develop naturally in the absence of fire, they share some species with oak hammocks that are the result of anthropogenic fire suppression. Oak hammocks may develop at old home or camp sites that were protected from fire; more frequently, hammocks invade pyric communities such as pine flatwoods or dry prairie that have been fire suppressed for long periods, eventually fire-proofing the area. Such anthropogenic oak hammocks generally have a depauperate shrub layer or may have a dense, nearly monospecific understory of saw palmetto (Serenoa repens).
Taken from: U.S. Fish and Wildlife Service. 1999. South Florida Multi-Species Recovery Plan. Atlanta, Georgia. Pp. 3:98-99, 103.
Listed Species Occuring in Mesic Temperate Hammock Habitat
- Florida Panther
- Key Deer
- Eastern Indigo Snake
- Kirtland's Warbler
- Bald Eagle
- Bachman's Warbler
- Audubon's Crested Caracara