MANGROVE ZONATION | MANGROVE FLORA AND FAUNA

ZONATION

In general, the following three conspicuous zones are identified.

1. Proximal Zone

This zone is towards water front, subject to regular tidal effect where intensity of soil accumulation and inundation is a continuous process. The mangrove species in this zone are specially adapted with stilt roots, prop roots for stability and anchorage. Main species with these features are Rhizophora apiculata and Rhizophora mucronata. On rocky and coral reef substrata, Avicennia, S. Caseolaris are also found. Both Avicennia and Sonneratia produce pneumatophores.

Above the Rhizophora/ Avicennia line luxuriant group of Bruquiera gymnorrhiza B. Cylindrica, Lumnitzera racemosa, L. littoralis, Ceriops tagal and Aegiceras corniculatum occur. Soil formation in the Core Zone is congenial for mangrove growth where in the trees attain a height of 10-15 metres in compact blocks. Ceriops and Bruguiera develop a strong hold fast in the form of knee roots or bent roots as a special adoption for supporting the erect bole.

Towards island area mangroves like Excoecaris agallocha, trees like Heritiera littoralis and xylocarpus spp. In association of Phoenix paludosa, Nypa fruticans, Acanthus ilicifolius and ferns like Acrostichum aureum occur, the latter occurring precariously in thick patches. Both Heritiera and Xylocarpus produce buttresses and help in containing soil in their cavities. Generally the salinity is on lower side in this Zone occurring towards hill sides where run off of fresh water is for a prolonged period. The duration of tidal submersion is low in this Zone compared to water front mangroves.

Being living resources, mangroves are self maintaining and renewable. For example as a coastal protection barrier, Mangroves maintain themselves at no cost and in the vent of tropical storm, the damages sustained will be self repaired without cost. Similarly both the direct and indirect harvests of products from mangroves are renewable yet, the mangroves resource is renewable only if the ecological processes governing the systm are maintained.
The leaf fall from the mangrove trees also contributes substantially to formation of detritus which supports coastal fisheries.
Mangroves constitute a unique habitat for wild animals and birds. They provide nesting breeding places for birds.
Mangroves provide breeding grounds for fish and other marine animals.
Mangrove serve as potential recreation site for fishing, boating, bird watching, sight seeing and photography. This has special significance for the Andaman & Nicobar Islands having tourism potential.
Mangroves provide vast scope for scientific and socio-economic studies.

Extraction of mangrove fuel and land development including agriculture has contributed to extensive damage of mangroves in some areas. Although damage to mangrove ecosystem from insecticides and pesticides used in agriculture and their run off, deliberate and operational discharges from ships, oil spills due to accidents and industrial outflows are not reported in the island, but these have caused extensive damage to mangroves ecosystem in other areas. Mangroves are traditionally used for aquaculture. There is tremendous demand for mangrove fish in international market. The prospectus of potentially quick economic games have caused a rapid rate of clearing of mangroves for development of brackish waterfish products. Excessive exploitation of mangroves could result in lower litter production and consequently could effect productivity of coastal fisheries.

Chengappa, in 1951 had estimated that Bruguiera species constitute about 26 to 30% of mangrove area of South and Middle Andaman Division. He prescribed clear felling and selection- felling of Bruguiera trees along with other natural mangrove trees. Although no systematic working of mangroves was followed in the subsequent years a small area was worked in North and South Andaman under selection system by removal of marked trees under the shelter wood system by removal of marked trees under the selection wood system, in which 40 well formed Rhizophora and Bruguiera poles per hectare were left out as standards uniformly spaced. Precautionary measures were also taken to leave protection belt of 20 metres width along the main creek on either side and 10 metres width along the smaller creek on either side to guard against sea erosion. Brush wood barriers across the creeks the were also left to hold the seeds of Mangrove species from washing away along with the tides.

In the past the mangrove forests were worked for extraction of fuel wood around Port Blair to meet the domestic requirement of the people. The Andaman Timber Industry and Chatham Power House were also using mangrove fuel wood for running their boilers. However, the mangrove fuel wood extraction and sale of mangrove has been totally stopped in the islands.

The limited extraction in the past of mangroves for fuel wood and poles from Government forest has not caused any damage to the Mangroves. But in the revenue areas, the destruction of mangroves is conspicuous and at places the area has been reclaimed for agriculture as well for settlement. The extent and condition of the crop and the threat under which such mangrove area lie presently is required to be assessed.

REFERENCE:
Text based on : ‘Mangroves of Andaman and Nicobar Islands’ by J.C.Dagar, A.D.Mongia and A.K.Bandhopadhya, 1991.·
SOURCE: http://forest.and.nic.in/default.htm