Indian has approximately 700,000 ha of area covered by mangroves along the estuaries and major deltas. There are vast degraded intertidal wetlands which can be used for various purposes. These areas can be brought to their pristine glory and high productivity by taking up large scale mangrove afforestation programmes along the coast.  
  

Mangrove is group of typical tropical and specialized trees growing in the saline and brackish water system. The mangrove trees are highly productive and economical which also protect the shoreline from erosion and cyclonic conditions. In India the total area covered by mangroves has been estimated to be about 700,000 ha. However these fragile and sensitive trees and their ecosystem have been abused, neglected and overexploited in India. The major threats to mangroves are deforestation, reclamation and lately pollution also.  

Why only mangroves   

The mangroves are angiosperms, with 45 species in India. They have special characters like viviparous germination, pneumatophores, prop or knee roots and salt glands. These trees form a thick forest belt on the deltas, along major estuaries, and fringe the estuarine banks, as well as backwaters. This unique tree resources is used for various purposes like tannin extraction, paper and pulp, firewood, timber, charcoal, fodder and several other by-products. The mangrove swamps are rich in the larvae of many economically important fishes, prawns, crabs and bivalves. These are the most suitable area for feeding, breeding and nursery grounds of these marine organisms and hence important for aquaculture purposes.  

Why mangrove afforestation   

Indian mangrove have been deforested and reclaimed to such an extent that the mangroves along the west coast are very much degraded. This has not only affected the coastline but also the fisheries to a large extent.  

Afforestation of mangrove areas on a large scale is the most urgent need of today, if the coastal environment is to be brought back again to its earlier pristine glory.  

Where mangroves grow   

Mangrove trees are found growing luxuriantly in the intertidal regions along the estuaries, backwater, islands and other protected areas. They generally prefer soft, clay mud for their growth. These species show different salinity tolerant limits.  

The expanse of mangrove forest depends on the intertidal expanse, substratum and salinity of soil as well as water. The inundation of the mangrove region during flood or rides is also one of the important factors.  

Which mangrove species to grow  

Out of 45 mangrove species occurring in India, some are true mangrove while others are considered as 'associated' flora. The most dominant mangrove species found along the east and west coast of India are listed below :  
  

Rhizophora mucronata   

R. apiculata   

Bruguiera gymnorrhiza   

B. parviflora   

Sonneratia alba   

S. caseolaris   

Cariops tagal   

Heretiera littoralis   

Xylocarpus granatum   

X. molluscensis   

Excoecaria agallocha   

Lumnitzera racemosa   

Avicennia officinalis   

A. marina 

How to identify the species   

Species are identified base on the leaf shape and details of the propagules (Seedlings) 

Mangrove seeds (fruits and seedlings) are always available in small quantity throughout the year. The main fruiting or seedling season, however, start from June to September, when plenty of seedlings of all the Rhizophoraceae, Avicennia and other can be collected.  

Which seedlings  

Only mature seedlings of these mangrove species should be collected for afforestation or nursery purpose. The seedlings of rhizophoracious trees have a podlike structure with tapering end of varying sizes and with typical morphological characters. Avicennia fruits are triangular in shape while Sonneratia is globular.  

Fruits or seedlings which are not fully mature or ripe may not grow further resulting into high mortality rate.  

How to store  

Different mangrove porpagules or seedlings have varying sensitivity for the period of storing.  

Species of Rhizophora, Avicennia, Bruguiera and Ceriops can be stores for 6 - 7 days in brackishwater. However, seedlings of Kandelia were observed to be very sensitive. Such seedlings are to be transplanted in the natural swamps or in polyethylene bags in the nursery immediately, where sufficient moisture or tidal water is available. Sonneratia fruits can be stored for a longer period.  

It is however, always advisable to store these seedlings partially immersed (pointed end in water) in seawater.  

How to plant   

There are two ways of planting the mangrove seedlings  

• Direct planting in the swamp
• Raising seedling in the nursery

Any intertidal area (between the high tide and low tide) where mangroves are absent and the substratum is of soft clay or mud and is inundated by regular tidal waters everyday, are suitable for direct mangrove planting. Select the sites where intertidal expanse is more. Along the Gujarat coast and West Bengal, where intertidal expanse is very large with highest tidal amplitude of 6 to 8 m, the upper limit of 1 m tidal water level has to be selected.  

Planning  

Before starting actual planting it is essential to make a tentative plan of the operation. How much area is available, which species to be planted and at what position of zonation pattern.  

Make suitable plots depending on the availability of the area. There should be a distance of about 10 m in between two plots. In case of fringing mangroves, where intertidal expanse is narrow, plot may be parallel to the shoreline. In larger areas plot may be either rectangular or square with a gap in between two plots. Planting of different species has also to be decided. Planting of seedlings may be undertaken according to the length of the propagules. Rhizophora mucronata or Rhizophora apiculata whose seedlings are the longest should always be planted towards the waterfront, these can be followed by Kandelia, Ceriops, Bruguiera, Avicennia, Lumnitzera etc. Species with smallest seeds like Sonneratia will come to the landward side of the intertidal expanse, followed by species of grasses and sedges.  

Direct planting method has to be used in open areas. The selected propagules or seedlings are transported to the site and planted. Care has to be taken that the pointed end of Rhizophora, Ceriops, Bruguiera and Kandelia seedlings should always be penetrated into the mud and the other blunt end, which is a shoot portion, should always be 6 - 8 inches above the sol level. Avicennia fruits are to be pressed gently into soil surface.  

Nursery techniques   

This method is useful where the mangrove species are not available in plenty. This also has many advantages, like selected species are available in large quantities. Mangrove nurseries can be developed in the upper part of the intertidal region where seedlings can be grown in polyethylene bags supported with bamboo’s. 

 

 Spacing between plants  

This is another important factor. Spacing differs according to the purpose for which the plants are grown, and also depends on the mangrove species grown  

However, for the plants suggested above the spacing between two plants may be about 1.3 m to 1.5 m.  

Aftercare    

One the plantation is established, then there is not much to be done. Only these plantations are to be protected from the grazing cattle, sheep’s and camels Periodical checking is helpful in finding out whether there is any need to replacement. But this is very minor.  

There is no need of any insecticide, pesticide, fertilizer, or anything but only protection. Plants will grow on their own.  
  

The mangrove nursery may be located near the estuary or sea where seawater or estuarine water is available. The nursery may be on the open ground or in the low lying protected areas where seawater reaches.  

The collected and selected seedlings are inserted in the polyethylene bags (4" X 10" size) filled with mangrove soil. If the nursery is on the raised ground then the perforations in the bags are not needed, but the nurseries in the low lying area need the perforations in the polyethylene bags.  

The seedlings thus grown, in different sizes of plots, anywhere else need watering everyday. However, the low lying intertidal areas get natural tidal waters twice every day.  

These seedlings may be allowed to grow upto the period of 6 months to 1 year and then depending on the requirement of species of the region, these can be transferred to the site in a boat or cart.  

The transplantation techniques may be same as indicated for direct planting. Only care should be taken to cut open the polythene bags at the base. Spacing may be the same depending on the purpose.  

What is the survival rate   

If due care is taken in selecting the seedlings used for plantation, then the survival rate is very high (about 90 to 95%). However, in polluted areas the mortality may be high because of toxic substances discharged from the industries. Therefore, it will be advisable to avoid such polluted areas. Sewage pollution or low level nontoxic pollutants may not have harmful effect on mangrove plants. On the other hand it has been found that mangrove trees can reduce the pollution by absorbing certain chemicals. Very high sediment load with fast current may also some time pose little problem  

Any poisonous plants ?  

There are no poisonous plant in mangroves. However, while handling Excoecaria agallocha care should be taken not to touch the milky juice to the eyes. This is harmful and sometimes leads to blindness.