270
e.g. presence of prop roots, pneumatophores, salt
exclusion, salt excretion and production of viviparous seedlings. The secondary productivity is
generally dominated by several species of crabs.
Further, mangrove wetlands have defi nite vegetation zonation patterns which may result from
each species’ optimal niche for productivity.
Mangroves suffer severe damage under fast environmental changes or during hurricanes.
However, damage could be mitigated if there is
freshwater or tidal fl ushing. Mangroves have to
spend possibly a greater percentage of their
energy for maintenance under high salinity conditions. Highest productivity occurs in riverine
forests, which are most open to both tidal action
and inputs of nutrients from adjacent uplands.
The dwarf mangroves are the least productive
systems. They occur under the nutrient- poor conditions, in hypersaline soils, etc.
The word ‘mangrove’ is derived from the
Portuguese word ‘mangue’ for ‘tree’ and the
English word ‘grove’ for a ‘stand of trees’. It refers
to both the dominant trees and the entire plant
community. There are many myths surrounding
the mangroves (Lugo and Snedaker 1974 ).
18.5.1 Geographical Extent
Mangrove swamps generally lie between 25° N
and 25° S latitudes. Broadly, mangroves are
divided into two groups, namely , (a) the Old
World mangrove swamps and (b) the New World
and West African mangrove swamps. The distribution of c 68 species of mangroves is believed to
be related to continental drift and, also, possibly
to transport by primitive humans (Chapman
1976a ). However, the distribution of these species is uneven. The swamps are particularly dominant in the Indo-West Pacifi c region (part of the
Old World group), where they contain the greatest diversity of species. There are 36 species of
mangroves in that region. Conversely, there are
only about ten mangrove species in the Americas.
Therefore, it is believed that the Indo-Malayan
region was the original centre of distribution of
the mangrove species (Chapman 1976b ). Some
of the most intact mangrove forests in the world
are certainly found in Malaysia, Micronesia,
around the Philippines, etc. Further, in Hawaiian
Archipelago, there are several mangrove species,
which are not native to the said place. But against
climatic odds and coastal geomorphology, they
had invaded the islands in the early twentieth
century. They are now permanent fi xtures on
coastlines there (Allen 1998 ).
18.5.2 Geomorphology
and Hydrology
There are different types of mangrove wetlands.
Each has a unique set of topographic and hydrodynamic conditions. Thom ( 1982 ) had developed
a classifi cation scheme of fi ve geomorphological
settings. These include systems dominated by
waves, tides and rivers, their energy sources, etc.
18.5.3 Hydrodynamic Classifi cation
It is important to note here that the development of
mangrove swamps is the result of topography, substrate and freshwater hydrology and tidal action.
Lugo and Snedaker ( 1974 ) and Lugo (in Wharton
et al. 1976) had developed a classifi cation of
mangrove ecosystems according to their physical
hydrologic conditions and had included six types.
Later, Cintron et al. ( 1985 ) had simplifi ed it into
four types, namely , (a) fringe mangroves including
overwash islands, (b) riverine mangroves, (c) basin
mangroves and (d) dwarf or scrub mangroves.
18.5.4 Salinity
The mangrove swamps are found under conditions which provide a wide range of salinity.
Some of the major points about salinity in mangrove wetlands have been summarised by Davis
( 1940 ) from his studies in Florida:
(a) Salinity shows wide annual variations.
(b) Salt water is not a prerequisite for the survival of any mangrove species. It only gives a
18 Classifi cation of Wetlands
e.g. presence of prop roots, pneumatophores, salt
exclusion, salt excretion and production of viviparous seedlings. The secondary productivity is
generally dominated by several species of crabs.
Further, mangrove wetlands have defi nite vegetation zonation patterns which may result from
each species’ optimal niche for productivity.
Mangroves suffer severe damage under fast environmental changes or during hurricanes.
However, damage could be mitigated if there is
freshwater or tidal fl ushing. Mangroves have to
spend possibly a greater percentage of their
energy for maintenance under high salinity conditions. Highest productivity occurs in riverine
forests, which are most open to both tidal action
and inputs of nutrients from adjacent uplands.
The dwarf mangroves are the least productive
systems. They occur under the nutrient- poor conditions, in hypersaline soils, etc.
The word ‘mangrove’ is derived from the
Portuguese word ‘mangue’ for ‘tree’ and the
English word ‘grove’ for a ‘stand of trees’. It refers
to both the dominant trees and the entire plant
community. There are many myths surrounding
the mangroves (Lugo and Snedaker 1974 ).
18.5.1 Geographical Extent
Mangrove swamps generally lie between 25° N
and 25° S latitudes. Broadly, mangroves are
divided into two groups, namely , (a) the Old
World mangrove swamps and (b) the New World
and West African mangrove swamps. The distribution of c 68 species of mangroves is believed to
be related to continental drift and, also, possibly
to transport by primitive humans (Chapman
1976a ). However, the distribution of these species is uneven. The swamps are particularly dominant in the Indo-West Pacifi c region (part of the
Old World group), where they contain the greatest diversity of species. There are 36 species of
mangroves in that region. Conversely, there are
only about ten mangrove species in the Americas.
Therefore, it is believed that the Indo-Malayan
region was the original centre of distribution of
the mangrove species (Chapman 1976b ). Some
of the most intact mangrove forests in the world
are certainly found in Malaysia, Micronesia,
around the Philippines, etc. Further, in Hawaiian
Archipelago, there are several mangrove species,
which are not native to the said place. But against
climatic odds and coastal geomorphology, they
had invaded the islands in the early twentieth
century. They are now permanent fi xtures on
coastlines there (Allen 1998 ).
18.5.2 Geomorphology
and Hydrology
There are different types of mangrove wetlands.
Each has a unique set of topographic and hydrodynamic conditions. Thom ( 1982 ) had developed
a classifi cation scheme of fi ve geomorphological
settings. These include systems dominated by
waves, tides and rivers, their energy sources, etc.
18.5.3 Hydrodynamic Classifi cation
It is important to note here that the development of
mangrove swamps is the result of topography, substrate and freshwater hydrology and tidal action.
Lugo and Snedaker ( 1974 ) and Lugo (in Wharton
et al. 1976) had developed a classifi cation of
mangrove ecosystems according to their physical
hydrologic conditions and had included six types.
Later, Cintron et al. ( 1985 ) had simplifi ed it into
four types, namely , (a) fringe mangroves including
overwash islands, (b) riverine mangroves, (c) basin
mangroves and (d) dwarf or scrub mangroves.
18.5.4 Salinity
The mangrove swamps are found under conditions which provide a wide range of salinity.
Some of the major points about salinity in mangrove wetlands have been summarised by Davis
( 1940 ) from his studies in Florida:
(a) Salinity shows wide annual variations.
(b) Salt water is not a prerequisite for the survival of any mangrove species. It only gives a
18 Classifi cation of Wetlands