Community
Types
Several
major types of mangrove communities are described
which result from differences in geological and
hydrological processes. Generally, mangroves grow
best in depositional environments with low wave
energy. Extreme wave conditions: prevent
establishment of propagules, destroy relatively
shallow root systems, and prevent accumulation of
fine sediments. The best sediment conditions are
fine-grained muds of silt/clay with lots of organic
matter. Primarily, these conditions exist along
deltaic coasts or estuarine shorelines. However,
all local species can grow on a variety of
substrates: sand, mud, rock, and peat. When found
on rock surfaces, it appears that they are growing
in sediment trapped in cracks rather than directly
on the rocky surface.
Riverine
forests
are tall flood plain forests along flowing waters
such as tidal rivers and creeks. Conditions are
favorable for extensive growth due to flushing by
daily tides. In addition, freshwater runoff and
terrestrial nutrient influx enhance this type of
mangrove community. Maximum heights of trees in
this community are 66 feet (20 m).
Fringing
forests
exist as a relatively thin fringe along waterways.
These forests appear to be flushed daily by tides,
but do not receive then amount of terrestrial
runoff as the riverine forests. Typically, the
classic mangrove zonation pattern of seaward
Red-Black-landward White scheme is exhibited in
this forest. Maximum heights of trees in this
community are slightly over 30 feet (l0
m).
Overwash
forests
exist as islands frequently washed over by tides.
All species are present with the Red mangrove the
dominant species. Typically, these islands develop
as a Red mangrove propagule strands in a shallow
flat. As more and more propagules strand and grow,
the island begins as a tangle
of prop roots.
As the island develops the roots eventually trap
sediment. Often, bare sand flats are found in the
center of these islandsThe maximum height of the
community is between 2&emdash;25 feet (7
m).
Scrub
or Dwarf forests
are common in the flat coastal fringe of southern
Florida and the Keys. All 3 species are present,
but height is limited to less than 7 feet (l.5-2 m)
except in depressions of mangrove peat. Nutrients
appear to be the limiting factors affecting growth,
although substrate (marl) is also
important.
Two
similar forests are the Basin and Hammock
communities. Basin
forests
are inland in depressions channeling terrestrial
runoff toward the coast. Trees in this community
have maximum heights of almost 50 feet (l5 m).
Hammock
forests
are in depressions but exist on slightly elevated
ground. In Florida, these communities exist in the
sawgrass communities of the Everglades. Trees
rarely growth height in excess of 17 feet (5 m).
Tidal flushing of both of the communities is
infrequent.
A
newer simplified system of mangrove community types
is now in use among researchers. It retains the
riverine and fringing forest types and omits the
overwash forest. Additionally, the scrub or dwarf,
hammock, and basin forests are lumped into the
category of basin forest. This scheme seems focus
on hydrological processes as the dominant influence
affecting community types. The fringing forest is
along waterways and bays. The riverine forests are
along tidal rivers and creeks. Inland of both of
these communities are the basin forests.
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