Vegetative Systems and Cover Types at the EMB

Major Ecosystems | Cover Types | Vegetative Zones (Cover Types)

Florida Power & Light Company's Everglades Mitigation Bank site is strategically located among

• Biscayne National Park on the east
• Everglades National Park on the west and
• John Pennekamp Coral Reef State Park on the southeast.

The location of this site places it in the unique subtropical climate of South Florida. The ecosystems in this area are unique -- and found nowhere else within the continental United States.

Following is a general description of the site along with comments on the specific plants found growing there.

Major Ecosystems

There are three major ecosystems found on, or immediately adjacent to, the Everglades Mitigation Bank site.

1) Card Sound Ecosystem

• by the Florida Keys on the east and southeast
• and the mainland on the west.
• opens mainly
• to the north into Biscayne Bay
• and to the south into Barnes Sound.
• is shallow with a depth of 3 to 12 feet and is saltier than the ocean.
• western portion has extensive mud flats near sea level while a few low sandy islands are located directly off the eastern edge. Major plant species found on the mud flats are
• turtle grass (Thalassia testudinum)
• manatee grass (Syringodium filiforme)
• and shoal grass (Halodule wrightii).

During the wet season, many varieties of floating or submerged algae are abundant. This ecosystem is a valuable nursery for numerous forms of animal life, because of the protection it affords.

Though the Sound is just outside the Bank site, it is very tightly linked to the biomechanics of the Bank itself.

2) Saline Mangrove Ecosystem

An important mangrove community consisting of dense stands of both red and white mangroves is found along the Card Sound shoreline. The saline mangrove ecosystem also contains

• an occasional black mangrove and
• a mixture of halophytic plants.

Black mangroves do not extend inland across wide tidal zones. White mangroves grow inland as far as one mile.

Heavy concentrations of mangrove are also found

• along the banks of the four historic tidal 'rivers' in the area
• and on inland tree islands with tidal connections.

Tides provide salt water for these areas.

The best-developed mangrove stands are found along the shoreline on mangrove flats, which are alternately watered by saltwater and rainwater runoff. Inland, as the water becomes brackish and then fresh, the red mangroves along the banks of the historic tidal 'rivers' are replaced by buttonwood and then swamp hardwoods.

3) Freshwater Marsh Ecosystem

During the rainy season, surface runoff overflows into adjacent mangrove zones to form a freshwater marsh. This marsh historically was connected to the vast Everglades system by the transverse glades. In some areas, the freshwater influences were sufficiently great that freshwater and brackish prairies extended very near to the shoreline. Rainfall and groundwater supply the majority of the freshwater now supplied to the EMB marshes. Marl or calcite and peat cover the bedrock limestone.

The flora of the freshwater marsh is varied. Sawgrass occurs throughout this system. Within the flat basins, the overlying peat is 2 to 5 feet deep and sawgrass will be the dominant vegetation. In the shallow marl soils, spike rush will gain in dominance. The one long-time tidal 'river' that originates within this zone is forested with freshwater swamp canopy vegetation.

Numerous 'tree islands' occur within the freshwater marsh. These clusters of woody or tropical climax vegetation dot the region. These islands are a sharp contrast to the herbaceous marsh species that surround them. They occur on a base of organic soil at slightly higher elevations than the surrounding marshes. Tree islands may include

• tropical hardwood hammocks
• buttonwood stands or
• sweetbay dornes.

These tree islands have adapted to flooding for short periods of time, but will not survive flooding lasting several months.

Both the saltwater marsh and freshwater mangrove ecosystems are found within FPL's Mitigation Bank.

Within these two major ecosystems are seven vegetational zones (cover types).

Cover Types

This general introduction of cover types or zones found at the EMB will be followed by a more detailed accounting in the next section: Vegetative Zones.

1) Sawgrass Marshes (also known as Sawgrass Marsh Zone)

Sawgrass (Cledium jamaicense) is structurally similar to herbaceous flats in being dominated by a non-woody species, but is distinguished here because it is a freshwater vegetation type. Other freshwater wetland plant species, including Periphyton, also occur here.

Animals found in this cover type include

• a variety of wading birds and
• the American alligator.

2) Wet Prairie (Wet Prairie Zone)

Dominated by sawgrass, this area is distinguished from its freshwater counterpart, sawgrass marsh, by the fact that it receives saltwater inundation during extreme storm events. Other salt tolerant plants common to this area include

• joint paspalum (Paspalum distichum) and
• seashore paspalum (Paspalum vaginiatum).

A variety of wading birds are typically found here.

3) Herbaceous Flats (Juncus-Disticalis Zone)

This area is dominated by herbaceous and generally halophytic or salt-tolerant species such as Borrichia, Spartina, Distichlis, Juncus and/or Eleocharis. There may also be varying amounts of other herbaceous or shrubby salt-tolerant species, such as Salicornia or Baccharis present.

The conspicuous animals found in this area include land crabs, fiddler crabs and a variety of wading birds. These species exhibit a range of tolerance for inundation and salinity factors.

4) Scrub and Dwarf Mangrove (Hypersaline Zone)

This cover type consists of

• short mangroves that occur in low density or
• dwarf mangroves, generally not taller than 3 - 4 feet high.

These are generally red mangroves with some black and white mangroves. Occasionally, species from the herbaceous flats cover type are mixed with the mangroves.

Animals found in this area include

• land crabs
• fiddler crabs and
• various spiders.

5) Dense Scrub Mangrove (Tidal Mangrove Zone)

Dense scrub mangroves some 10-12 feet high, primarily red mangroves but including some black and white mangroves as well, dominate this community. The cover type is located behind the coastal band or along the four historic estuarine rivers. Periphyton is not as conspicuous in this cover type as it is for the coastal band mangroves.

Animals found in this area include

• fiddler crabs and
• various spiders.

6) Coastal Band Mangroves (Coastal Mangrove Zone)

This cover type is dominated by tall mangroves ranging 20-30 feet high, primarily red mangroves with some black and white mangroves in areas of slightly higher elevation. Occasionally, white mangroves dominate the community. This community is located along the open coastlines. Periphyton covers the tree roots.

Animals found in the coastal band area include

• fiddler crabs and
• a varied assortment of spiders.

7) Coastal Ridge Mangroves (Ridge Mangrove Zone)

These are very tall mangroves, 25-35 feet high. They are predominately white and red mangroves with a few black interspersed. These are very productive trees that also serve the vital role of stabilizing this vulnerable ridge from wave erosion. Australian pine is gaining a foothold on the ridge and, because of their shallow, dense root system, they can impede sea turtle egg deposition.

Animals found in this area include

• the endangered Atlantic green turtle (Chelonia mydas mydas) and
• fiddler crabs.

8) Historic Estuarine 'Rivers'

There are four of these features located within FPL's EMB site. Two of them are large enough to travel through several of the site's cover types. The red and white mangroves that predominate in these systems grow much taller than the mangroves of surrounding zones. Near the sources of these 'rivers,' more whites and buttonwoods are found. The largest river crosses into the sawgrass marsh zone and as it does, sweet bays, dahoon holly and buttonwood replace the mangroves.

Animals found here include

• wading birds
• nesting birds
• sheepshead minnows and
• snakes.

9) Exotic Communities

This cover type is being included here to stress the importance of the potential harm these invasive exotic plants can evoke on native South Florida ecosystems.

The two main exotics found at the EMB site are

• Australian pine (Causuarina equisetifolia) and
• Brazilian pepper (Shinus terebinthifolius).

These are found primarily

• within the fresh water systems of the Sawgrass Marsh and
• along all major soil disturbances within the site.

Vegetative Zones (Cover Types)

The FPL Environmental Mitigation Bank site contains several different vegetation zones and habitats. From the northwest to the southeast, the characteristics of the land change from

• fresh water sawgrass to
• wet prairie to
• juncus salt marsh grassland to
• scrub mangrove.
• mangroves are found along the coast. Throughout these main communities are tree islands where land elevations are slightly higher.

The following is a more detailed inventory of the vegetation cover types found within the EMB site. The major species of each zone are listed within this segment of the text. A more detailed inventory of all plants found within each zone is included in the Cumulative Vegetation Inventory.

1) Sawgrass Marsh Zone - Fresh Water

Located predominately between U.S. 1 and Card Sound Road, this area supports a wide variety of herbaceous plants. The predominant species is the scrub sawgrass (Maricus jamaicensis). Others include

• green buttonwood (Conocarpus erecta)
• small dog fennels (Eupatorium capillifolium)
• pennywort (Hydrocotyle umbellata)
• Florida paspalum (Paspallum floridanum)
• climbing hempweed (Mikania scandens)
• bushy lippia (Lippis nodiflora)
• India goosegrass (Eleusive indica) and
• rosy-camphorweed (Pluchea rosea).

Within the sawgrass marsh are true islands that have been colonized by woody plants. The predominant vegetation found here are

• green buttonwood (Conocarpus erecta)
• Dahoon holly (llex cassine)
• southern bayberry (Myrica cerifera)
• cocoaplum (Chrysobalanus icaco)
• Brazilian pepper (Schinus terebinthifolius)
• false willow (Baccharis halimifolia)
• eastern false willow (Baccharis halimifolia)
• pond willow (Salix caroliniana)
• Australian pine (Casuarina equisetifolia)
• sabal palm (Sabal palmetto) and
• saw palmetto (Serenoa repens).

2) Wet Prairie Zone - Fresh to Brackish

This zone is south of the sawgrass marsh.

The predominant species is the scrub sawgrass (Maricus jamaicensis). Interspersed within this zone are

• joint paspalum (Paspalum distichum)
• seashore paspalum (Paspalum vagianatum)
• black sedge (Schoenus nigricans)
• swamplily (Crinum americanum)
• seashore saltgrass (Distichlis spicata) and
• saltwort (Batis maritima).

Tree islands in this area contain

• green buttonwood (Conocarpus erecta)
• Dahoon holly (llex cassine)
• guiana rapanea (Raponea quianen)
• poison ivy (Toxicodendron radicana)
• white mangrove (Laguncularis racemosa)
• pond willow (Salix caroliniana)
• muscadine grape (Vitus rotundifolia)
• Brazilian pepper (Schinus terebinthefolius) and
• Australian pine (Casuarina equisetifolia).

3) Juncus-Distichlis Marsh Zone

This zone lies to the east and south of the L-3IE Canal and emergency evacuation route for the Turkey Point Power Generation Facility. The predominant vegetation is

• saltgrass (Disticalis spicata)
• black rush (Juncus roemerianus) and
• sea oxeye (Borrichia frutescens).

There are many pools of water where the red mangrove (Rhizophora mangle) grow. Other species that grow within this zone are

• green buttonwood (Conocarpus erectus)
• white mangrove (Laguncularia racemosa)
• scrub sawgrass (Mariscus jamaicensis)
• southern milkweed (Asciepias viridula) and
• eleocharus (Eleocharus cellulosa).

Within the Juncus-Distichlis marsh are free islands that are colonized by the more woody species. The vegetation found on the slightly higher elevation islands include

• green buttonwood (Conocarpus erectus)
• red mangrove (Rhizophora mangle)
• white mangrove (Laguncularia acemosa)
• black mangrove (Avicennia germinans)
• Australian pine (Casuarina Equisetifolia)
• nightshade (Solanum verbascifolium)
• false willow (Baccharis angustifolia)
• golden leather fern (Acrostichum aurem) and
• sea oxeye (Borrichia frutescens).

This zone is occasionally colonized by more freshwater species when the rainfall is plentiful. However, storm surges of saltwater quickly kill large numbers of these plants causing this zone to be unstable.

4) Hypersaline Zone

a) Hypersaline Zone - Scrub (Dwarf) Mangrove (0-1.2m)

This zone contains low open stands of red mangrove (Rhizophora mangle) interspersed with very few white mangrove (Laguncularia racemosa). Saline to brackish water lies in this area for most of the year, except in the center of the tree islands. The species found within this zone are

• seashore saltgrass (Distichlis spicata)
• red mangrove (Rhizophora mangle)
• white mangrove (Laguncularia racemosa)
• black rush (Juncus roemeriamus)
• Virginia glasswort (Salicomia virginica) and
• sea oxeye (Borrichia frutescens).

Within these zones are tree islands that have soiling elevations that are slightly higher. The tree islands are dominated by the red mangroves but a large number of white and black mangroves are also found, along with sedges, grasses and herbs around the island margins. The dominant vegetation is as follows:

• red mangrove (Rhizophora mangle)
• green buttonwood (Conocarpus erectus)
• white mangrove (Laguncularia racemosa)
• black mangrove (Avicennia germinans)
• saltgrass (Disticalis spicata)
• black rush (Juncus roemerianus)
• Virginia glasswort (Salicornia virginica)
• saltwort (Batis maritima)
• fuirena (Fuirena scirpordea) and
• sea oxeye (Borrichia frutescens).

b) Hypersaline Zone - Low Dwarf Mangroves (0-0.5m)

This zone contains very diminutive open stands of red mangrove (Rhizophora mangle). The soil and miter is extremely saline due to reduced freshwater flushing and evaporation of sea water from Card Sound that enters this zone during extreme high tides. The predominant species in this zone are short 12-to-18-inch red mangroves with very few and much reduced leaves.

This zone is characterized by a white marl soil of freshwater origin, soil saltiness twice those of the open waters of Card Sound, and extremely poor plant growth. The salt water intrusion and seedling distribution by hurricane tides have established principally red mangroves within this generally stressed environment. These mangroves are physiologically different from the same species that are found growing in the adequately flushed tidal areas. The mangroves of this association are characterized by

• stunted growth
• wide spacing
• erratic fruiting
• poor seedling survival and
• an almost complete absence of leaf litter.

Within this zone are tree islands that have slightly higher soil elevations. These islands are dominated by

• red mangroves (Rhizophora mangle)
• white mangroves (Lagunculana racemosa)
• black mangroves (Avicennia germinans)
• saltwort (Batis maritima) and
• black rush (Juncus roemerianus).

5) Tidal Mangrove Zone (0-10m)

This zone contains dense stands of red mangrove (Rhizophora mangle) and white mangrove (Laguncularia racemosa). The mangroves within this area receive a regular flushing of the sounds tidal waters during seasonal high tides. The resultant cleansing and nutrient flush allow these trees to grow in a more productive manner.

6) Coastal Band Mangrove Zone (0-20m)

This narrow zone lies landward of the shoreline ridge of Card Sound. The trees found here are

• red mangrove (Rhizophora mangle)
• white mangrove (Laguncularia racemosa) and
• black mangrove (Avicennia germinans).

These mangroves are tall, though somewhat smaller than those on the adjacent coastal ridge. Biomass production in this area is substantial and input to the food chain by leaf fall is considerable. Marine grasses and macroalgae are found here, particularly within the tidal meanders.

7) Coastal Ridge Mangrove Zone (0-25m)

This zone is a narrow, elevated ridge that partially extends through the EMB site. The ridge hosts

• red
• white and
• some black mangroves.

These trees are tall and productive.

The exotic Australian pine (Caesarian ecluisetifolia) has invaded this ridge.

8) Estuarine River

This is being included within this section for the purpose of stressing their importance in the ecology of the South Dade Mitigation Bank site. There are four of these features within the bank site. Two of these are sufficiently large enough to travel through several of the bank cover types.

The largest of these riverine systems travels along the cast side of U.S. 1 and is bisected by the levees of the L-31E and the Sea Dade Canal. This estuarine river hereafter referred to as Historic 'River' #1 continues to the north of the bank site by approximately 2,000 feet. The estuarine rivers host a rich diversity of plant arid animal life due in part to their reduced topography, which allows tidal flushing much further inland there is allowed on the adjacent hypersaline flats. As a direct effect of the depressional nature of this system, fresh water will naturally flow into it more readily from the surmounting areas within the Juncus-Distichlis marsh. This allows a mixing of fresh and saline water to create highly productive brackish conditions.

To the north of the levee of the L-31 E, where water impoundment has created a completely fresh water environment, the plant communities found growing on the banks are subtropical hardwoods. These riverine systems are extremely important as they provide water during times of reduced rainfall for aquatic insects and fish that the higher organisms require for nourishment.

9) Major Exotic Vegetative Species

Australian pine (Casuarina equistefolia) is a fast-growing productive species. It has become a pest plant because its growth is unchecked by parasites and feeding by local herbivores. It produces a thick layer of fallen needles on the forest floor because the needles are not eaten by other organisms. This profuse litter supplies smothers native seedling development and research is being conducted to verify the belief that an allelopathic substance released by the needles retards seedling germination and growth.

Australian pine can be found growing within the FPL South Dade Mitigation Bank along the east side of U.S. 1 and along the west and east side of Card Sound Road. It has infiltrated into the tree islands to the sawgrass marsh. The tree islands that are inhabited are colonized by a few trees clustered on the highest ground near the center of the islands. For the most part, Australian pine that is found within Phase 1 is not found in the lower sawgrass plain. There is an exception to this along the southeast quadrant of Phase 1 to this area, the Australian pine are peppered throughout the sawgrass.

Proceeding east of Card Sound Road toward the FPL Turkey Point Power Generation Facility cooling canals are the canals of the L-31E and the Sea Dade canal. These two canals have allowed the Australian pine to travel along their lengths because of the disturbed, well-drained soils of these banks. A triangle-shaped portion of land -- completely cut off from normal sheet flow by the confines of Tallahassee Road on the west, Sea Dade canal on the north and the 1--31E canal on the south -- has an altered hydroperiod and an additional land disturbance of a raised roadway that bisects this triangle. Without intervention, this area could easily evolve into a monocultural stand of this species.

Brazilian pepper (Schinus terebinthifolius) is also a fast growing exotic species. The tree tends to form dense; monospecific stands where it is allowed to get a foothold on disturbed areas. The major areas where this plant can be found are along the roadways or levees that cross the Mitigation Bank site or within the tree islands that dot the sawgrass marsh that lies between U.S. 1 and Card Sound Road.

The Brazilian pepper has not dominated the tree islands, but has infiltrated a niche at the interface between the tree island and the space that is intermediate between elevation, hydroperiod and function between the native wetland type of vegetation and the upland vegetation of the hammocks. It is not known whether the pepper will stabilize at this niche or eventually out-compete the native vegetation and become monocultures. The species' rapid growth rate, coupled with the high survival of the seedlings due to a lack of grazing by herbivores, enables the plants to shade out other natives.

The brightly colored berries of the Brazilian peppers are eaten by a number of birds. However, the attraction for the berries may be for the narcotic effect of two specific tricyclic terpenes that they contain rather than for their nutritional value (Workman, 1978). Raccoons are also known to eat the berries, but their scat will exhibit a large number of undigested whole berries indicating poor digestibility. There is little documentation of the food value of the detritus they deposit nor how it is incorporated into the food web).

10) Rare and Endangered Plants

FPL's EMB site hosts more than 185 plant species. Of that number, 24 are considered by the State of Florida to be endangered, threatened or commercially exploited species.

The following are the descriptions found in the Inventory of Rare and Endangered Flora of Florida:

Endangered: Species in danger of extinction if the deleterious factors affecting their populations continue to operate. These are forms whose numbers have already declined to such a critically low level, or whose habitats have been so seriously reduced, or that, without active assistance, their survival in Florida is questionable.

Threatened: Species that are likely to become endangered in the state within the foreseeable future if current trends continue. This category includes

• species in which most or all of the population is decreasing because of over-exploitation, habitat loss, or other factors, and
• species that may still be relatively abundant but are being subjected to serious adverse pressures throughout their range.

Species of Special Concern: Species that clearly do not fit into the above-mentioned categories, yet warrant special attention. Included in this category are

• species that, although they are perhaps presently relatively abundant and widespread in the state, are especially vulnerable to certain types of exploitation or environmental changes and have experienced long term population declines and
• species whose status in Florida have a potential impact on endangered or threatened populations of the same or other specials outside the state.

Commercially Exploited: Species that are vegetatively attractive for human landscape purposes and, as a result, are 'collected' from the wild by individuals who wish to profit from the market for these plants. Continued collection patterns have the propensity to reduce the numbers of a specific species below a critical threshold and this is why these specie are listed by the state.