Coastal dune and strand
The coastal dune and strand includes beaches and the vegetation zones occurring landward of the open sandy beaches.
The vegetation of the beaches and foredunes is characterized by pioneer plants able to establish themselves in the shifting sand. Typical species include railroad vine ( Ipomoea pes-caprae ), seashore paspalum ( Paspalum vaginatum ), sea oats ( Uniola paniculata ), and inkberry ( Scaevola plumieri ). Inland from the dune crest cabbage palm ( Sabal palmetto ), seagrape ( Coccoloba uvifera ), and buttonwood ( Conocarpus erectus ) are typically found. The vegetation tends to change from grassy to woody from the foredune inland to the more protected back dunes.
Dune and strand communities are adapted to the severe stresses of shifting sands, a highly saline environment, high winds and surf. In some instances, salt spray plays a role similar to fire in other ecosystems by retarding succession indefinitely at a shrubby or grass stage.
Historically, impacts to coastal dune and strand plant communities (sometimes the total loss of the community) have resulted from beachfront residential development; invasion by exotic vegetation, primarily Australian pine ( Casuarina spp. ); and accelerated erosion of beaches due to maintenance of inlets or nearby tourist and residential development.
Dry prairies are generally described as having essentially the same features as pine flatwoods, but without pine trees ("treeless plains"). They are open, grassy expanses often intermediate between wet grassy areas and forested uplands and occur on typically acidic, nutrient-poor, sandy soil and usually flat, rocky terrain. Scattered cypress domes and cabbage palm and hardwood hammocks are often interspersed within dry prairies.
This community is dominated by many species of grasses such as broomsedge ( Andropogon virginicus ) and wiregrass ( Aristida stricta ). Saw palmetto ( Serenoa repens ) is the most common shrubby plant over large areas, with rusty lyonia ( Lyonia ferruginea ), staggerbush ( Lyonia fruticosa ) and shiny blueberry ( Vaccinium myrsinites ) common in places. A number of herbs and sedges are also found within dry prairies.
Fire is important in determining the composition of the vegetation and its suitability for different species of wildlife. Winter burning associated with cattle operations may have shifted this community from forbs and grasses to saw palmetto. Absence of fires may result in shrubby communities or even successions into pine flatwoods, while frequent fires which occur during the growing season yield more herbaceous environments.
Large areas of dry prairie have been converted to improved pasture, and this trend is continuing. Recent expansion of citrus production southward is probably responsible for most dry prairie losses at this time.
Pine flatwood occurs on low, flat terrain and is characterized by an open overstory of slash pine ( Pinus elliottii var. densa) , with low shrubs such as saw palmetto ( Serenoa repens ), rusty lyonia ( Lyonia ferruginea ), staggerbush ( L. fruticosa ), and gallberry ( Ilex glabra ) and a wide variety of grasses and herbs as groundcover. The soils of flatwoods are sandy with a moderate amount of organic matter in the top few centimeters and an acid, organic hardpan one-third to a meter below the surface, which impedes both downward and upward water movement. Flatwoods are often interspersed by and merge with many other vegetation types (e.g., scrub, hammock, cypress swamps).
Hydric pine flatwoods typically have standing water for one to three months a year, and have a wetland plant understory. "Scrubby flatwoods" are ecotonal between pine flatwoods and scrub, found at elevations intermediate between these two habitat types.
Fire strongly influences pine flatwood community structure, as it reduces competition from hardwoods, thus maintaining pine flatwoods as stable, essentially non-successional communities. Historically lightning was the source of fires, but now many flatwoods are managed by controlled burning.
Changes in both moisture and fire regimes have resulted in changes in plant species composition and wildlife values. Residential development is rapidly eliminating this plant community (and all other upland communities).
Xeric oak scrub is the oldest habitat type in peninsular Florida, and Collier County contains its southernmost extension. This habitat typically occurs on high, sandy dune ridges that are remnant shorelines formed by higher sea levels during the Pleistocene. The soil is composed of well-drained, sterile sands, virtually devoid of silt, clay, and organic matter, and extremely nutrient-poor.
Xeric oak scrub is a xeromorphic low scrub community, dominated by a layer of evergreen (or nearly evergreen) oak ( Quercus spp. ), or rosemary ( Ceratiola ericoides ), or both; with or without a slash pine overstory. Groundcover is low consisting of sparse herbs, tufted grasses, lichens ( Caledonia spp. ), and spike moss ( Selaginella spp. ); saw palmetto is often present. Unvegetated sandy areas, or bare areas colonized by a lichen layer are common.
The xeric oak scrub is essentially a fire-based community. Ground vegetation is extremely sparse and leaf fall is minimal, thus reducing chance of frequent ground fires so important in the community. As the slash pines and scrub oaks mature, however, they retain most of their branches and build up large fuel supplies in the crowns. When fires do occur, this fuel supply, in combination with the resinous needles and high stand density, ensures hot, fast-burning fires. Such fires allow for regeneration of the xeric oak scrub community, which would otherwise pass into a xeric hardwood community.
Xeric oak scrub and its ecologically important variations are seriously threatened. Citrus production and especially residential development have eliminated much of this plant community. In addition, isolation from fire has resulted in succession to xeric hardwood hammock with a relatively closed canopy, thereby reducing its value to most endemic animals and plants.
Hammocks are discrete, narrow bands of vegetation that occur at elevations somewhat higher than surrounding areas, forming unique "habitat islands". These habitat islands contain biotic, topographic, hydrologic, and edaphic (soil) elements distinctly different from surrounding habitats. Hammocks are typically dominated by non-deciduous hardwoods, such as oaks or redbay; cabbage palm hammocks often occupy slightly elevated sandy ridges near the coast. Hammock systems may be made up of several different arborescent assemblages for which the dominant hammock type is named. However, an element common to almost all hammocks is high species diversity; this creates an inherent value in these habitats by maintaining more resources (niche elements) to be exploited by the resident species.
A unique component of hammock systems is the epiphytic (air plant) community, which includes many protected species of ferns, bromeliads, and orchids. Southern Florida contains the largest number of epiphytes in the continental United States Epiphyte populations are not well developed or diverse unless they are able to mature in systems that provide diversity in substrate (host trees), insects for pollination and nutrition, high humidity and rainfall, sunlight, and a dense tree canopy to moderate heat stresses due to intense mid-day sunshine.
Occurrences of these communities can be a possible indication of the presence of pre-Columbian civilization remains. Many of the most diverse and spectacular hammocks in Collier County exist (or formerly existed) on coastal, prehistoric shell midden mounds created by the native peoples of the area.
As these hammock systems are typically found on elevated soils, they are often among the first properties considered for urban development. Development may eliminate the hammock entirely, or it's alteration may change its internal environmental conditions, and lower its species diversity.
The occurrence of tropical species within hammock systems increases closer to the coast, where the warm waters of the Gulf of Mexico and the effects of occasional frosts are more completely attenuated during the winter months. This allows cold sensitive tropical species to survive and compete in protected coastal areas. The most diverse of these communities are typically dominated by tropical species that have origins in the Caribbean, South America, or Central America; these are therefore regarded as "tropical hammocks". These again occur usually as disjunct habitat islands.
Tropical hammocks typically have very high plant diversity, containing over twenty-five species of trees and almost fifty species of shrubs and small trees. Typical tropical trees and shrubs are the strangler fig ( Ficus aurea ), gumbo limbo ( Bursera simaruba ), mastic ( Mastichodendron foetidissimun ), Graytwig ( Schoepfia chrysophylloides ), ironwood ( Eugenia spp. ), and Jamaica dogwood ( Piscidia piscipula ). Epiphytes, vines, and ferns are often abundant. Tropical hammocks contain a number of plants that are extremely rare in the U.S.
The tropical hammock is the successional climax for much of the uplands of extreme south Florida. Because of susceptibility to frequent fires, this community is mostly confined to islands or slightly wetter areas but may invade drier areas if fire is removed for any length of time.
Tropical hammocks have been largely lost to residential development in most areas of Collier County, except for the few that remain on isolated islands and on state lands.
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