The protection from cyclone damage afforded by the Bangladesh Sundarbans mangrove forests, a continuous natural mangrove forest of 5800 km2 in the south-west of Bangladesh, led the Forest Department in 1966 to commence a programme of planting mangroves outside the protective coastal embankments in order to provide greater protection for inhabited coastal areas. These initial mangrove plantings were highly successful and led to the development of a large-scale mangrove afforestation programme. To date, more than 120,000 ha of mangroves have been planted. Nursery and planting techniques have been developed for the major species, while additional species are still being investigated. As a result of the extensive monospecific plantations, however, outbreaks of two major insect pest species have been observed. In addition, a number of other problems were also encountered but in terms of coastal protection and stabilization, wood production and land reclamation, large-scale mangrove afforestation appears to be both technically possible and socio-economically beneficial.
Bangladesh Sundarbans mangrove, 21.9497274, 89.18333039999993
Country or Territory:
Estuaries, Marshes & Mangroves
Area being restored:
in excess of 120,000 hectares
Primary Causes of DegradationMining & Resource Extraction, Urbanization, Transportation & Industry
As in other parts of the world, mangrove degradation is a growing problem in Bangladesh and is attributable to changes in the physical environment (e.g. changed sedimentary condition, increased salinity, etc.), as well as human encroachment and overexploitation of resources. The focus of this project is not only on rehabilitating these degraded areas, but also using afforestation to create coastal buffer zones for protection against cyclones and tidal surges and to accelerate the accretion of coastal char lands in order to prevent erosion and create more cultivable land.
While the initial objective of the afforestation programme was to create a shelter belt to protect the lives and properties of the coastal communities, the early success of the plantations resulted in the setting of additional objectives for coastal afforestation, including to: (a) provide forest products for a range of uses; (b) develop forest shelter-belts to protect life and property inland from tidal surges; (c) inject urgently needed resources into the national economy (i.e. timber and land); (d) create employment opportunities in rural communities; and (e) create an environment for wildlife, fishes, and other estuarine and marine fauna.
The project does not have a monitoring plan.
Coastal afforestation staff from each district–Patuakhali, Barisal, Noakhali, and Chittagong–have been responsible for establishing mangrove plantations with assistance from local villagers.
Description of Project Activities:
From its limited beginnings in 1966, annual plantings of approximately 320 ha (800 acres) of mangroves were undertaken on newly accreted land in the Patuakhali, Barisal, Noakhali and Chittagong coastal districts. These plantations were established by the respective district coastal afforestation staff with assistance from the local villagers. Techniques to raise suitable seedlings and to establish the plantations were developed by 'trial and error'. Although roughly 27 species of mangroves and a similar number of mangrove associates occur in Bangladesh, most are rare, or of little economic importance. Only 10 or so species occur frequently enough to sustain silviculture. As a result of the early trial and error approach to plantations, only two species, Sonneratia apetala and Avicennia officinalis, showed encouraging survival rates, and, as a consequence, these two species dominate the mangrove plantations generally as monospecific stands. These species are medium quality timbers used for fuel wood, constructions and furniture. About 80% by area of the early plantations consisted of monospecific stands of S. apetala, about 15% consisted of stands of A. officinalis with the remaining areas consisting of Excoecaria agallocha, Bruguiera spp. and Ceriops decandra, more valuable species for timber or paper pulp production. Polybag culture of a range of other mangrove species has been experimentally developed although field assessments of the performance of these species are as yet incomplete. Nursery and planting techniques vary considerably among the various species: Sonneratia apetala Mature green fruits of keora (S. apetala) are generally collected during September and they are heaped for 20 days to allow the pericarps to decay. They are then rubbed and washed in water to separate the small seeds from the rotted fleshy portion of the fruits. About 1 kg of green fruit will yield about 275 g or 7500 seeds. These seeds maintain their viability for about one month. Approximately 7-8 kg of these seeds are broadcast onto intertidal nursery beds 1.2m wide and 12m long, slightly raised above the surrounding sediment. The beds are usually encircled by low (15 cm) earthen walls which retain water pumped into the enclosures during unusually dry periods. Germination onset and success is largely controlled by salinity which needs to be maintained below 20ppt; above 20ppt germination performance declines rapidly. The seedlings are allowed to grow for about 10 months and from each nursery bed about 2350 seedlings of the desired height (30-60 cm) become available for the next suitable planting season, i.e. from July to August. At this time, the seedlings are gently pulled out of the ground and packed for transport to selected afforestation sites. Generally, one such nursery bed provides sufficient seedlings to plant an area of 0.4 ha at the usual spacing of 1.2 Á— 1.2 m. The uprooted seedlings can be stored in the shade for up to 6 days without any significant losses. As discussed later, this approach results in adequate survival rates for a species that has not been cultivated elsewhere. Excoecaria agallocha Seeds of this species ripen in August. The seeds retain their viability for about one month and can either be sown directly onto sheltered intertidal areas, or may be raised in nurseries. Although nursery raising is not used for large plantings, some polybag seedlings are allowed to grow for about 12 months and seedlings of the desired height (30-50 cm) become available for planting from July to August. At this time, the seedlings are packed for transport to afforestation sites where they are usually planted out at a spacing of 1-0 x 1.0 m. One-year-old seedlings may also be collected from the floor of natural forests of the Sundarbans and rapidly transported to planting sites where they are usually planted on relatively raised lands. Because this species is mostly planted onto more raised lands, survival rates using these planting techniques are around 80% after 12 months. Avicennia oflicinalis The crypto-viviparous 23 propagules of species of Avicennia are usually collected from around the base of mother trees in August to September. When kept in air, these propagules lose their viability within a few days. These propagules may be directly planted into sheltered areas by 'dibbling'-where the propagule is gently pushed into the soft sediment until firmly wedged. 'Dibbling' is usually undertaken during neap tide periods to allow the seedling to develop roots. Pre-treatment of the propagules has also been used to decrease the establishment time. Such treatment consists of placing the propagules in small nets and exposing them to daily tidal inundation to hasten the decay of the pericarp. Removal of the pericarp by pre-treatment reduces the establishment time to 2-3 days compared with the 5-6 days required where no pretreatment is used. Alternatively, propagules may be raised in nursery beds that are exposed to daily tidal inundation. Seedlings are raised for about 1-2 months after which they are gently pulled out of the ground and packed for transport to afforestation sites where they are usually planted out into holes of 3 cm diameter at a spacing of 1.0 x 1.0 m. Recent experiments using one-year-old seedlings (ranging in height from 70 to 90 cm) raised in nursery beds and planted out at Chittagong and Barisal, showed high survival rates, and may prove to be more suitable for areas where larger seedlings are required.
Ecological Outcomes Achieved
Eliminate existing threats to the ecosystem:
Because of the highly dynamic nature of the Bangladesh coastline, survival of mangroves is generally poor and replacement planting often needs to be undertaken for up to 3 years. In sheltered localities, however, survival is usually around 70% (see next section). Long-term survival (i.e. between 5 and 15 years) is also highly variable, but in experimental plots at Barisal, survival in 5-year old S. apetala ranged from 29 to 52%. Quantitative data for A. officinalis is still being collated but initial analyses suggest approximately 30-60% survival rates after 5 years in the Chittagong coastal district. Planting during June to August appears to result in maximum survival of newly planted seedlings of S. apetala based on replicate plots where fixed numbers of seedlings were planted out from nurseries every month over a 24-month period. Cyclical regression analysis of these data shows that not only the time of planting but the age of seedlings is a contributing factor, and that seedlings older than 12 months generally result in lower survival rates for equivalent months. While quantitative field trials have not yet been carried out with A. officinalis, maximal survival of this species also appears to occur during June to August. In some areas such as the Chittagong and Noakhali Divisions, winter planting is considered to result in higher survival rates but, to date, no experimental data support this view. At 1.2 x 1.2 m spacing, the trees become congested within 4 or 5 years. In such dense Sonneratia and Avicennia plantations, thinning is carried out after 9-10 years when up to 50% of the stems may be removed. Thinning of these plantations largely consists of removing stunted trees and cutting smaller stems from multi-stemmed trees, and results in slightly reduced natural mortality together with marginal annual increases in height and girth. In more widely spaced plantations, thinning is generally not required because of the relatively slow rate of tree growth and the loss of some trees in plantations due to stem borer attack (see below). Increases in height and girth, and thus volume, depend on the initial spacing of the particular plantation. In 5-year-old plantations of S. apetala, maximal heights are attained at a spacing of 0.85 x 0.85 m while maximal girth is found in plantations where the initial spacing was 2.4 x 2.4m. Maximal wood production for this species of 18.5m3/ha/year occurs at an initial spacing of 1.2 x 1.2m. With an initial spacing of 1.2 Á— 1.2 m, acceptable volume increments are found in some species throughout the coastal regions. For other genera such as Bruguiera, Ceriops and Xylocarpus, poor growth performance occurs throughout the coastal regions, and is attributable to poor species-to-site matching, particularly in relation to interstitial salinity and tidal inundation.
Factors limiting recovery of the ecosystem:
The mangrove afforestation project in Bangladesh is being carded out in one of the most dynamic natural environments on earth and as such, some problems associated with land stability must be expected and can never be completely eliminated. Four types of land stability problems have been recognized including: burial of mangrove seedlings when and where sediment accretion rates are particularly high; smothering of seedlings by sand in areas where wave action reworks large volumes of sand shorewards; the winnowing of fine sediment (clay and silt) from the plantation site during prolonged stormy periods, leaving a mobile sandy lag deposit; and the erosion of plantation margins through bank slumping by migrating tidal and river channels. All four types of coastal change have caused the loss of mangroves from existing plantations. However, the increasingly systematic identification of areas with land stability problems is being used to avoid planting sites where the risk of crop losses between planting and harvesting is high. In this way, mangrove losses due to adverse coastal changes should be progressively minimized. Other problems in relation to mangrove plantations have been identified. Over and above the generally difficult communication and logistic conditions in the coastal areas, these problems include unauthorised cattle and buffalo grazing and the illegal occupation of newly raised land by the local villagers for cultivation of rice. In the mangrove nurseries, one of the initial problems encountered was that heavy rains during the early nursery period caused low seedling production, usually because the seeds are light and easily floated away. In addition, early planting trials of other mangrove species using the technique where seedlings are pulled out of the ground, did not provide acceptable levels of survival, presumably due to root damage during seedling extraction. The high proportion (about 80% by area) of S. apetala in early plantations is partly due to the tolerance which this species shows toward this transplanting procedure. Polybag culture is now used to raise seedlings of at least 10 different mangrove species for growth trials, and these show much better performance in terms of survival and growth after out-planting. Nevertheless, the extent of the early monospecific plantations has led to outbreaks of two major pest organisms: Keora stem borers: Zeuzera conferta (Cossidae: Lepidoptera) Stem borer infestations of S. apetala plantations have increased markedly over the last five years apparently with the increased area of monospecific stands of this species. In I988, a mean of 52% of the trees were affected with 22%, 17% and 13%, respectively, showing severe, moderate or slight infestations. Although stem borer attacks generally do not kill the trees, they reduce their timber value, and the Protection Division of the Forest Research Institute is presently trying to develop control measures. At the same time, the PTU is evaluating the silvicultural control of this insect through multi-specific plantations, particularly mixtures of Sonneratia and A vicennia. Leaf defoliators: Streblote siva (Lasiocampidae: Lepidoptera) The numbers of this insect have also increased in apparent response to large monospecific stands of S. apetala. As with the stem borer, this species generally does not kill the trees but severe infestations may cause growth deformities and a marked decline in growth generally and wood production specifically. The silvicultural control of this insect through multi-specific plantations, particularly mixtures of Sonneratia and Avicennia is currently under investigation by the PTU.
Socio-Economic & Community Outcomes Achieved
Economic vitality and local livelihoods:
On current estimates, there are some 96,000 ha of suitable coastal lands presently available for further plantations. Despite this, it is estimated that a total of 150,000 ha has been reclaimed and stabilized since the inception of this programme. Considerable areas (60,000 ha) have now become raised to the level where they are no longer suitable for further mangrove plantations and these are currently planted with salt-tolerant upland trees (e.g. Acacia nilotica, Albizia procera, Samanea saman, Casuarina equisettfolia) or have been transferred from the Forest Department to the local people for grazing cattle, goats and buffalo. More importantly, the protection and stabilization has provided 60,000 ha of stabilized land which at current land values ($US 800/ha), suggests that the real success of the coastal plantations has been to generate 1.44 x 10-9 Takas from new agricultural lands. In addition, it is estimated that the plantations have provided more than 600,000 m3 of wood (Ishtiaq Uddin Ahmed, Assistant Conservator of Forests, personal communication, 1991) and other forest products, and have provided in excess of 5 Á— 10-6 man days employment for local villagers over the last 25 years, considerably adding to the economies of coastal villages. During the intense cyclone of April 1991, many of the mangrove plantations were damaged. The intensity of damage was higher along the Chittagong cottst than in the western part of the coastal belt but none of the mangrove nurseries sustained any significant damage. Young plantations (1-5 years old) seemed to have suffered most damage through wave action, with leaf loss ranging from 10 to 80%, By July 1991, however, most of the plantations showed clear signs of recovery (N. A. Siddiqi, unpublished data, 1991), and it is expected that full recovery will occur with the exception of those areas where excessive silt deposition resulted. Damage to non-mangrove species raised on the coastal embankments (such as Acacia nilotica) was significantly higher than that to mangroves, and less developed root systems in non-mangrove species may have contributed to their susceptibility to 'wind-throw'. Consequently, it may be argued that the most significant benefit provided by the mangrove plantations was the provision of a self-repairing system which facilitated the stabilization and protection of the coast during intense cyclonic conditions.
Key Lessons Learned
There are several important lessons emanating from this programme which have wider application. From an ecological management perspective, the major lesson to date has been that monospecific mangrove cultures may develop problems which are difficult and costly to remedy. Where the economic conditions are as they are in Bangladesh, then silvicultural control measures need to be investigated rather than to rely on chemical control measures. More importantly, plantations need to be designed as multispecific systems to minimize or avoid some of the identified problems. In that sense, silvicultural research should precede any intensive planting programme.
In some instances, mangrove plantations have had a sacrificial value, i.e. they have caused such rapid accretion that the land no longer supports mangroves. Because using mangrove plantations to accelerate the accretion of new land is not necessarily compatible with optimal timber production, the objectives for afforestation need to be reviewed and clearly prioritized.
Finally, the changing soil salinities as well as soil maturation of the newly accreted lands require an integrated programme of sequential planting of suitable species which are able to adapt to the changing conditions. In contrast to the existing situation, such an integrated programme requires the long-term control and tenure of the land by the Forest Department.
Despite the improvements that could have been made to this programme at its inception, it has nevertheless proved successful in most respects and illustrated that large-scale mangrove afforestation is both technically possible and socio-economically beneficial.
In 1985, the mean yield of wood from 10-year-old plantations was estimated at 200 m3/ha, providing an MAI of 20 m3/ha.
Because of purchaser preference, the price of Sonneratia as fuel wood is approximately 2 Taka ft 3 while other popular fuelwoods are generally priced at 15 Taka ft 3 even though Sonneratia has a slightly higher calorific value (8236Btu/lb) when compared with mango (7886 Btu/lb) and raintree (8191 Btu/lb). Thus, from a purely economic perspective, while the price of Sonneratia as fuel wood remains low, the cost of thinning is barely recoverable. One of the options currently being evaluated is to design the plantations so as to optimize timber productions without the need for thinning.
On the basis of experimental trials it was found that an adjustment of density so that in 5- or 6-year-old plantations, densities of 1100-1600 trees/ha occurred, would result in marginally increased diameter increment, and hence, volume. Such an adjustment of density may be achieved either by thinning when plantations are 5 or 6 years old, or by adjusting the initial spacing so that this density is attained by natural attrition around 5 or 6 years after planting.
If the products of thinning are an important outcome from the coastal plantations, and if these can be harvested economically, then it seems that the current spacing of 1.2m x 1.2m should be retained, with thinning carried out when the plantations are 5 or 6 years old. However, as there is some doubt on the economics of thinning, it may be preferable to adjust the initial spacing to achieve the desired density 5 or 6 years after planting out. An initial spacing of 1.75 m x 1.75 m will result in the desired densities after 5 or 6 years through natural losses and, would thus reduce the initial labour involved in establishing the new plantations. On the other hand, such wider initial spacings would require monitoring to ensure that unforeseen physical events, for example, have not caused major departures from the predicted survival rates. In addition, some infilling may also still be required as mortality may occur in patches rather than randomly through newly established plantations.
Sources and Amounts of Funding
Up to 1996, the afforestation programme was funded by the World Bank and the Government of Bangladesh, through the Ministry of Environment and Forests.
Saenger, P. and N.A. Siddiqi, 1993. Land from the sea: the mangrove afforestation program of Bangladesh. Ocean & Coastal Management 20: 23-39.
Bangladesh Forest Research Institute