Mangrove forests have favourable silvicultural characteristics which lend themselves to intensive forest management for wood products. Some of these characteristics are as follows:
- Rapid growth: mature stands under suitable conditions may yield over 270 m3/ha within 30 years, equivalent to an MAI of 9-10 m3/ha.
- Good regeneration potential: most mangrove species flower and fruit regularly and the propagules are dispersed by tides. Thus, mangrove stands can recover rapidly from natural or man-made disturbances, including intensive logging.
- Tendency to form homogeneous/even-aged stands: pure stands of Rhizophoras or Avicennias are not uncommon and even in mixed stands, the principal components are restricted to a handful of species.
- Diversity of forest products: a wide range of products are produced and as bioenergy plantations even the smaller thinnings may be used as firewood.
Under favourable conditions, mangrove trees can grow to large sizes. Rhizophoras over 40 m tall are not uncommon and individuals over 62.5 m have been reported (Sukardjo, 1978). However, large trees are becoming scarce, especially in South East Asia, as most of them are removed before they can attain such sizes.
Rhizophora spp. are however, not valuable as timber because of their tendency to split and warp when dried. The wood is dense and difficult to work. The sapwood is easy to preserve but not the hardwood. It is resistant to decay but not to marine borers. Its possible uses include agricultural implements, boat construction (knees and ribs), general heavy construction (rafters, beams, joists), marine and bridge construction (underwater, non-teredo infested waters), marine and bridge construction (above water), fence posts and poles. In the Ca Mau peninsula in Southern Vietnam, a small amount of Rhizophora is used for walling and flooring.
The wood of Rhizophora is exceedingly heavy with a specific gravity varying from 0.8-1.2. Avicennia, which has a lower density (about 0.64) and good nail holding qualities, is often used as railway ties in Cuba. In Venezuela Avicennia nitida is used as mining props, telegraph and transmission poles.
In the Bangladesh Sundarbans, Heritiera fomes (Sundri) is the prime timber species used for house and boat construction, while the tops are used for hardboard and as firewood. Creosoted Bruguiera gymnorhiza transmission and telegraph poles were used in the Andaman Islands.
Rhizophora spp. are preferred for charcoal making. Their moisture content (MC) when felled is about 40 percent (as percent of oven dry weight) compared to Avicennia wood which ranges from 70-95 percent. Rhizophora wood dries to about 25 percent MC after two months, whereas Avicennia requires up to six months to dry to 35 percent MC. This partly explains the popularity of Rhizophora wood, as predrying stock can be kept to a minimum. Other species (Bruguiera gymnorhiza and Ceriops sp.) are also used but in smaller quantities.
Charcoal is the main mangrove product in Thailand, Peninsular Malaysia, Sumatra (Indonesia), Myanmar and Southern Vietnam. Industries are well developed at the village and cottage industry levels in most Asian countries where mangroves still abound. Charcoal is mainly used for cooking purposes and small-scaled industries.
Rhizophoras are favoured as fuelwood for domestic purposes and are commercially removed as in the case of Malayisa and Thailand, or collected by fishermen and villagers.
In Singapore, Hongkong and Malaysia, there is an established demand for mangrove piling poles used in land reclamation and the construction industry. Used in wet sites which are not infested by shipworms, such mangrove piles can outlast non-treated inland hardwoods.
Along the coastal waters, Nibong (Oncosperma filamentosa) is normally used as fishing stakes in Southeast Asia, but sometimes mangrove poles are also used. These have to be regularly replaced.
Along the muddy river banks, small fishing stakes are used to support tidal fish nets. Mangrove poles are also used for scissor nets in housing construction. In countries in South East Asia, fishermen cut mangroves and dump them into the shallow coastal waters as a way of creating shade and thus attract fish (fish attraction devices).
Gewa (Excoecaria agallocha) is the principal pulping species used in the newsprint mill in Bangladesh. Sonneratia caseolaris, Excoecaria agallocha, and Avicennia marina produce strong Sulphate pulps.
Large mangrove concessions have, in the past been granted for chipping operations in the east Malaysian states of Sabah and Sarawak and in Indonesian Kalimantan and Sulawesi based on Rhizophora and Bruguiera spp. The chips were exported mainly to Japan for making dissolved pulp and cellulose derivatives such as rayon, used in the textile industry.
Rhizophora bark produces very fine tannin suitable for leather work. Tannin from mangrove species has also been used for curing and dyeing of fishing nets made of natural fibre to make the nets more resistant to biological decay.
The production of tannin has declined greatly in recent years, in particular since local demands have been reduced after the introduction of nylon fishing nets and the use of chrome as the predominant agent for leather curing.
Sukardjo, S. 1978. Some aspects of Mangrove Ecology. Training Materials for Forestry Officers. FAO/UNDP/BGD/84/056, Integrated Resource Development of the Sundarbans Reserved Forest. Rome, FAO.
FAO. 1994. Mangrove forest management guidelines. FAO Forestry Paper No. 117. Rome.