Community Types and Zones
Some of Florida’s mangrove forests are nearly 80 feet tall while others are more of a bushy-scrub than a forest. These differences are the result of different environmental conditions, such as topography, type of growing surface (rock, silt, sand), tidal action, freshwater inputs, nutrient availability, and climate. Although mangroves grow in a wide range of environmental conditions, they have been classified into 4 major types: riverine, fringe, basin, and dwarf.
Riverine mangroves occur along tidal rivers and creeks and may be several miles inland from the coast. They receive nutrients from both upland and estuarine sources, and fresh water flushing lowers the salt stress. These favorable conditions make the riverine mangrove forest very productive and trees there may grow over 80 feet tall.
Growing conditions for fringe mangroves are less favorable and trees will seldom grow to half the height of those in a riverine environment. Fringe mangroves form a thin border along protected shorelines. Examples are the mangrove forests lining the Keys and Ten Thousand Islands. They receive little freshwater or nutrients from the land, and are vulnerable to high winds. Many of the small islands are actually over washed on a daily basis during high tide.
Basin mangroves are located inland from fringe and riverine mangroves in depression basins. They are only flushed by infrequent extreme tide events. The resulting stagnant, salty conditions exclude red mangroves and limit the growth of black and white mangroves to less than 30 feet high.
Dwarf mangroves may only grow to 5 feet tall in 50 years. The stunted growth can be the result of extremely salty conditions, severely nutrient poor environments, or colder climates.
In general, the 4 species of mangroves sort themselves into the tidal zone where their adaptations give them a competitive advantage (Figure ? Photoshop composite illustration of mangrove zones.) For example the stilted, lenticil covered roots of the red mangroves allow them to grow in the deepest part of the tidal zone and they dominate the fringe community. In contrast, the pneumatophores of the black mangrove are too short to function well in a zone of high tidal fluctuation. But they are better adapted to survive the higher levels of H2S that occur in the more landward basin community that has less tidal flushing. White mangroves are also tolerant of high H2S and salt, but their seedlings grow best in high light zones, such as openings created by lightning fires or wind damage. Buttonwoods are the least tolerant of salt and they are usually upland of the tidal zone and frequently transition into the tropical hammock. In addition to adaptive based zones, the smaller propagules of the black and white mangroves are more likely to wash further up the tide zone than the long, bottom dragging, red mangrove propagule. Mangrove zones are a useful concept based on observations and ecological principles. However, in the complex, changing, and chaotic coastal environment the different species are frequently observed “out of place".
Environmental factors and adaptations
