Coastal Plantation

Coastal Plantation the plantation forest on the maritime belt. Mangrove afforestation was initiated along barren shoreline and offshore islands, between 21-23° N and 89-93° E in 1966, with the assistance from the World Bank. About 130,000 ha have so far been planted. This is important not only to mitigate loss of lives and property from cyclones and tidal surges, but also to generate employment opportunities, and produce wood for consumption. Commercially important mangrove species, viz, Sonneratia apetala, Avicennia officinalis, A. marina, A. alba, Amoora cucullata, Bruguiera sexangula, Excoecaria agallocha, Xylocarpus mekongensis, Heritiera fomes, Ceriops decandra and Nypa fruticans were planted on new accretion; of them S. apetala proved itself to be the most successful one. A. officinalis showed good performance only in the eastern coastline. At present, S. apetala constitutes about 94.4% and A. officinalis about 4.8% of successful mangrove plantations.

The shoreline of Bangladesh is about 700 km long. The coastal areas with mangrove plantations are regularly inundated during high tide. However, the forest floor of the older plantations is not submerged in the dry seasons during neap tides. Soil texture ranges from silty loam to silty clay loam. pH varies between 7.5 and 8.2. Afforestation is carried out on a very unstable environment. Thus, there will always be a risk of some plantation loss during the time it takes the trees to reach maturity. Both S. apetala and A. officinalis are pioneer species in the ecological succession in the natural mangroves of Bangladesh. These species grow well on new accretions with regular inundation. They are strong-light demanding. These might be the reasons why these species have performed better. In the case of S. apetala plantation is carried out using seedlings, whereas, this is done by dibbling seeds into the mud for A. officinalis.

New alluvial lands are flat and available on the rivers, estuaries and seacoasts. There is little site preparatory work in coastal afforestation activities. After surfacing of the land above water, grasses (Portesia coarctata and Myriostachya wightiana) make their appearance. Planting is undertaken before the grass gets thick during the monsoon. The seedlings are planted when they are about 0.6 m in height. The uprooted seedlings are packed and carried to the planting sites by boat. Neap tides are chosen for planting. This reduces the chance of tide water stagnation for a long time and enables proper and efficient planting work for a longer time. Vacancy filling and sometimes replanting are carried out to establish well-stocked plantations. Weeding is not required as the initial growth of seedlings is quite fast. Earlier, a spacing of 2.4 m x 2.4 m was followed. A greater proportion of plantations was raised at a spacing of 1.2 m x 1.2 m. Presently, a spacing of 1.5 m x 1.5 m is practised for S. apetala and 1 m x 1 m for A. officinalis. The growth of S. apetala varies greatly from place to place. Productivity tends to increase from east to west of the coastal belt. On a good site a stand may attain an average height of about 20 m with a diameter of 20 cm at breast height in 20 years. Productivity may be up to 10 m3/ha/year. A rotation age of 12-15 years has been found suitable. However, harvesting of the crops has yet not been undertaken for various reasons.

Problems of plantation Coastal plantations encounter many problems which include: (i) Insect infestation- infestation in S. apetala plantation is common all along the coast. The overall infestation was estimated to be about 52%. Raising mixed plantations instead of monoculture has been suggested to overcome the problem. The major pest is the bee-hole borer, Zeuzera conferta (Cossidae: Lepidoptera). (ii) Raising mixed plantations- monoculture either with S. apetala or A. officinalis is the characteristic of coastal plantations. Both are pioneer species in ecological succession and other species have not been found suitable for initial plantation. Scope exists only for establishing mixed plantations in combination with S. apetala and A. officinalis for silvicultural control of insect pests but that has not yet been found feasible. (iii) Natural regeneration - artificial regeneration is expensive and it is inconvenient to develop multi specific forest by this method. It can be avoided if natural regeneration is adequate for the development of a second rotation crop. Regeneration by natural means is lacking in coastal areas. (iv) Second rotation crop - in order to maintain a continuous forest cover in the coastal areas and to enhance production of the coastal forest while S. apetala is maturing, underplanting is highly desirable. Successful underplanting will also result in the creation of mixed and multi-storied forests with more valuable species. [Neaj Ahmad Siddiqui]

See also tidal forest.