Silviculture of Mangrove Forest

“Mangrove” constitute plants of intertidal tropical forest community, they are dicotyledonous shrubs or trees, confined to tropics. More precisely they are defined as trees confined or restricted to intertidal or its adjacent communities.

Habitat The mangrove trees adopted themselves in habitat where there is regular exposure and immersion by the tide, low dissolved oxygen in water, high H2S (hydrogen sulphide) content, high humus, irregular salinity, tropical and frequently high temperature. Mangrove occur in low wave action areas. High growth of mangroves can be seen in protected lagoons, estuaries of rivers and coastal lakes. High humidity, high rainfall, minimum air temperature and seasonal air temperature variations (not exceeded by 100 C) are favourable factors for the growth of mangroves.

Characteristics of Mangrove Swamps Mangrove swamps are formed on the silt which is washed down by rivers and creeks, and which, subject to occasional erosion, gradually spread seawards, the mangrove spreading with it and helping, by means of its dense growth and mass of roots, to hold up the silt and form new land.

Distribution Mangrove forest is found in littoral regions throughout the tropics. In the Indo-Barman region the mangrove forests are distributed to a greater or less extent in suitable localities throughout the coastal regions, delta of indus, west coast of peninsula, from sundarbans southwards along the east coast of the peninsula and down coast upto Burma. Also along the coast of andamans and adjacent islands.

Root-system The root-system of the mangroves is highly specialized. In the case of Rhizophora the lower part of the stem dies early, and the stem is supported by numerous stilt-like roots which raise it above the mud, while aerial roots are sent down from the stem and branches and anchor themselves in the ground.

Leaf structure The habitat of mangroves, namely swampy ground impregnated with salt, is a physiologically dry one, and the leaves of the trees therefore possess a marked xerophilous structure, “with a thick cuticle, large mucilage-cells, protected stomata, and especially a large-celled thin-walled, aqueous tissue, the dimensions of which increase with the age of the leaf and with the corresponding rise in the amount of salt contained. Old leaves serve essentially as water-reservoirs for the younger leaves.

Germination One of the most interesting characteristics of the Rhizophoraceae (most common family) is that they exhibit vivipary. The fruit is indehiscent, and there is no resting stage for the embryo as in the case of normal seeds. As soon as the fruit is fully developed the embryo commences to grow inside it.

Silviculture system for mangrove forest The working of mangrove forest is carried out under different methods. The coppicing and pollarding capacity of the different species have not been studied in detail. In unregulated felling's rough pollarding is often carried out. working plans for mangrove areas in the prescribe coppice felling under a rotation of five years in one case and ten years in another. Larger trees which have been pollarded are said to have thrown out vigorous pollard-shoots. In the Federated Malay states the selection system is in operation, the felling cycle being twenty years, and the minimum felling limit being a girth of 1ft at 41/2 ft above ground level.

Importance of mangroves: a) Mangroves have a complex root system which is very efficient in dissipating the sea wave energy thus protecting the coastal areas from tsunamis, storm surge and soil erosion. Their protective role has been widely recognized especially after the devastating Tsunami of 2004. b) Mangrove roots slow down the water flows and enhance sediment deposition. C) They act as a fertile breeding ground for many fish species and other marine fauna.

Food chain in mangroves: Due to estuarine ecosystem and majority of estuarine animals, one group of animals may exhibit or occupy two or more habitats. Most of the fauna are detrivorous and create detritus food chain. Phytoplankton and the different microbes associated with decomposition of leaf litters, are providing food in this ecosystem. The zooplankton, benthos and other terrestrial and aquatic vertebrates and invertebrates act as consumers in which in which tiger is occupying a unique position, being at the top of the pyramid in this food chain.

Plantation and restoration of mangrove forest:

The major stages in project implementation included site selection, awareness generation and training, species selection, plantation activities and monitoring.

Artificial regeneration- 1. Nursery beds were prepared in the inter-tidal belts of the selected areas. The nursery operations typically started in monsoon, from July, and continued till November-December. The transplantation of nursery-raised plants was done in January- February. 2. Raised Earthen Mound Technique: This model was one of the preferred options due to its cost effectiveness. The model is also easy to implement in cases where large areas are to be brought under mangrove cover. This technique has proved to be effective in terms of survival rate in adverse ecological conditions. 3. Direct Dibbling: This method can be employed at places where tidal current is low. It is also amethod that can be used to cover maximum area in a limited time frame. The gaps, if any, are filled through nursery-raised seedlings. This model has proved to be cost-effective and result –oriented. 4. Propagules Plantation: Propagules of different species have been planted to increase the biodiversity of mangroves in certain areas.