0703-B2

Tree Stand Improvement Initiatives for Increasing Tree Resources of Bangladesh Sundarbans

Mohammad Osman Gani^[1]

Abstract

The Sundarbans Reserved Forest is very rich in flora and fauna and many of these are economically very important. A large number of people are dependent on the Sundarbans for their livelihoods as it supplies a large number of products. There has been a tremendous decrease in the stocks of economically important tree species due to continuous harvesting for a long period of time. Tree Stand Improvement initiatives were taken at different times to improve the tree resource. Under the Sundarbans Biodiversity Conservation Project an attempt has been made to improve the tree stock through Enrichment Plantation and Assisted Natural Regeneration treatment. The initial methodology of fencing plantations along the boundary with simple seedling planting and jungle cutting has been modified with the introduction of soil work, addition of gypsum and individual seedling fencing, which is better in terms of growth and survival. It is believed that these Tree Stand Improvement initiatives will be able to increase tree stocks on an average from 50 to 400 per ha over about one third of the area of the Sundarbans.

Introduction

The Sundarbans Reserved Forest (SRF) of Bangladesh is considered as one of the largest and oldest managed mangrove forest of the world. It is situated in the south-western part of Bangladesh between latitude 21⁰ 39' 00'' and 22⁰ 30' 15" N and longitude 89⁰ 02' 00" and 89⁰ 54' 07" E in the estuary of the river Ganges. The total area of Sundarbans Reserved Forest (SRF) is about 6 017 sq. km, out of which 4 143 sq. km is landmass and balance 1 874 sq. km is water bodies (Canonizado and Hossain 1998). The Sundarbans flora is characterized by the abundance of trees like Heritiera fomes Buch.-Ham., Excoecaria agallocha L., Ceriops decandra (Griff.) Ding Hou., Bruguiera gymnorhiza L., Sonneratia apetala Buch.-Ham., Xylocarpus granatum Koen., Xylocarpus mekongensis (Lam.) Roem., Rhizophora mucronata Poir., Avicennia officinalis L. and palms like Nipa fruiticans Wurmburg and Phoenix paludosa Roxb. The SRF is also quite rich in shrubs and herbs. The important shrubs are Hibiscus tiliaceus L., Acanthus illicifolius L., Brownlowia tersa (L.) Karst. and herbs are Acrosticum aureum, Tamarix troupii Hole, Aegilitis rotundifolia Roxb. and Pandanus foetida Roxb. Prain (1903) recorded a total 334 plant species of 245 genera, many of them are economically very important. The SRF is also rich in fauna. It is the home of Royal Bengal Tiger (Panthera tigris L.). The forest has been divided into three zone viz. fresh water (171 838 ha), moderate saline (178 081 ha) and saline (251 511 ha) zone.

The Sundarbans is the single largest source of supply of timber, fuelwood, pulpwood, thatching material, honey and a whole array of non-wood forest products for Bangladesh. It is known that about 3.5 million people living along the fringes and within 25 km radius from the fringes are dependent on SRF (Anon. 2000). The H. fomes composes about 63 percent of the total flora of the Sundarbans, which is economically very important and major revenue of the SRF is derived from it. Sundri (H. fomes) is the most important and most abundant timber resource of the Sundarbans. It is believed that the word Sundarbans comes from "Sundari Ban" in Bangla, which literally means Sundri Forest. Besides H. fomes, X. granatum, X. mekongensis are timber of very good quality. E. agallocha is used to manufacture newsprint and match sticks and C. decandra is used as fuelwood. Nipa palms are used as thatching materials for roofing rural houses. Major fuelwood is collected from C. decandra and smaller quantities of fuelwood are collected from Cynometra ramiflora L., Amoora cuculata Roxb. and H. tiliaceus.

The forest has been under the management of Forest Department from the year 1884, where selection system controlled by area was practiced for harvesting forest produce (Heinig 1892). Economically important trees like H. fomes, E. agallocha and C. decandra were harvested in each year on the basis of fixed diameter prescribed in the management plan leaving all other trees below that diameter to grow in the specified area of the forest. The same area is felled at the completion of felling cycle of 20 years. There was a dramatic decrease in the economically important timber species especially H. fomes, E. agallocha, X. granatum and X. mekongensis along with the loss of biodiversity (Sattar and Faizuddin 1998) and (Gani 2000). Tree Stand Improvement (TSI) initiatives were taken in different time to increase tree resource in order to improve the productivity as well as biodiversity of SRF.

Materials and methods

The TSI history of the SRF dates back to 1877 when an experimental plantation of Baobab tree (Adansonia digitata L.) and Bamboo (Bambusa tulda Rox. and B. balioa) was made in the fresh water zone. The Forest Department implemented some TSI programme from the year 1976 upto 1991. An area of 1 133 ha has been planted in different locations of the SRF (Karim 1995). The mesophytic and mangrove species were planted at a spacing of 1.8 m X 1.8 m and 1.2 m X 1.2 m respectively. The performances of these TSIs were reviewed while conducting this study. Here the plantation programme has been termed as TSI initiatives as it is related to stand treatment and planting of tree species (Benthem 2001).

The plantations of mesophytic species were established in the raised areas of fresh water zone. Here the land was out of reach of tide water during the dry period of the year (November to April), when the water turns to saline. The same land is inundated during the wet part of the year (May to October), where no salinity exists in the water due to on rush of fresh water. The mangrove species were planted in moderately saline and saline zone, which is inundated round the year. The Forest Department maintains journal for all the TSIs but no growth information were recorded in them. These TSIs were quite successful. It was observed in the mesophytic plantations that there was no regeneration of the mangrove species though there were profuse regeneration of the same in the adjacent areas under the mangrove cover. The performance of the mangrove TSIs was excellent and it was difficult to differentiate the plantation from the natural forest. Lot of undergrowth of other mangrove species found in the mangrove TSIs.

Under the Sundarbans Biodiversity Conservation Project (SBCP), TSI initiatives are being implemented from the year 2000, which will continue upto the year 2006. Here three categories of TSIs were implemented viz. (a) Enrichment plantation, (b) Assisted Natural Regeneration (ANR) and (c) N. fruiticans plantation. It is known that 1 069 ha of Enrichment plantation and 3453 ha of ANR and 495 ha of N. fruiticans plantation has been established in the SRF by the year 2002 (Benthem 2001), which was shown in Table 1. Enrichment forms of TSIs were implemented in the areas where the canopy closure is less than 30 percent. Nursery raised seedlings were planted in the Enrichment Plantations. The N. fruiticans plantations were established on the newly surfaced area where the inundation takes place round the year but it was not considered in this study.

Table 1: Area of TSI initiatives implemented in the SRF.

The ANR was implemented in the areas infested by climbers, creepers, and bushes such as H. tiliaceus, A. ilicifolius, A. aureum and P. foetida and Derris trifoliata Lour. The dense undergrowth vegetation suppresses growth of desired seedlings particularly H. fomes, X. mekongensis, B. gymnorhiza and E. agallocha. The ANR treatment followed the removal of undesirable species of climbers, creepers and bushes. Here, limited amount of pruning was also carried out in order to open up spaces for sunlight. The performances of these TSIs were reviewed in this study. The TSIs were fenced all along the boundary except the waterfront.

Latter on, the methodology of establishing the Enrichment and ANR form of TSI were changed. Before establishing enrichment plantations, a small soil work is done to free the compacted soil by digging holes of 0.5m X 0.5m X 0.5m size and breaking the clods before the monsoon that is in the month of May and mixing the soil with 250 g of Gypsum. The place is marked with small pegs and planting is carried out in the month of June. The planted seedlings were fenced with the help of nylon net, which can last in the saline water for a period of 2 to 3 years. It was expected that by the time the seedlings would attain the height free from browsing by deer. Normally the target is to plant 500 seedlings per ha. The growth data were recorded in the TSI.

For ANR, some changes were made in order to have much success than the initial method of implementation. Here the cut bushes were distributed in a scattered way all over the ANR treatment area manually, which in fact will impede the movement of the deer in the TSI areas to save the emerging seedlings from deer browsing. Additional seedlings were also planted like the enrichment one in the ANR if the quantities of seedlings are less than the expected one. Here the planted seedlings were also fenced with the help of nylon nets.

Results

The initial successes of establishing TSIs were not satisfactory, as the continuous fencing could not solve the browsing problem. The deer entered the plantation either by jumping over the fence or through the wholes created due to the rotting of stacks or through swimming from the opening at the waterfront. Moreover, the TSIs located at the western part of the SRF in the saline areas suffered from stress due to the lack of inundation and increased salinity during the dry part of the year. The initial success in the first few months after planting was quite good but subsequently the condition of the plantation was not encouraging. The expensive TSI turned to a plantation with very few seedlings.

On the basis of the performance of the Enrichment plantation, certain treatments have been done in the implementation of TSIs. The seedlings were planted in the pits where soil work has been done and addition of Gypsum was made in order to counter the stress due to salinity. The soil work will eliminate the compactness of soil. This will help to keep the soil soft and moist, which is necessary for the survivability of seedlings. The seedlings were fenced by net to protect against browsing. The height growth of the planted seedlings was recorded from the field and data of the treated one was compared with the non-treated one for Enrichment planting. It was observed that the height growth of H. fomes, X. mekongensis, B. gymnorhiza and A. officinalis increased by 25, 28, 40 and 35 percent respectively in the untreated plots in one hand and on the other hand the height growth of H. fomes, X. mekongensis, B. gymnorhiza and A. officinalis increased by 43, 45, 80 and 70 percent respectively in the treated plots within a period of 6 months (June, 2002 to November, 2002). The survivability of the seedlings was 95 percent for the treated plots as compared to the 40 percent for the untreated plots of Enrichment plantings.

Discussion

There were 4-detailed inventories on the tree resources of the SRF. Curtis (1933) carried out the first detailed inventory in the year 1929, second one by Forestall in the year 1960, third one by the Overseas Development Agency (ODA) in the year 1983 and 1984 and fourth one by Cannonizado and Hossain in 1995 and 1996. The data of the first inventory is not available. Data of the remaining inventories were used in this study. There were 511, 296 and 295 H. fomes trees per ha of 10 cm diameter at breast height (dbh) and above and 211, 125 and 102 H. fomes Sundri tress per ha of diameter 15 cm dbh and above in the Forestal, ODA and FRMP inventory respectively (Table 2). There was a 42 percent reduction in the number of trees per ha between the Forestal and ODA inventories for H. fomes 10 cm and above in dbh. The annual reduction over the 37 years between the Forestal and FRMP inventories are 2.95 trees per ha per year. Between the ODA and Forestal inventories, the reduction rate is 18.4 percent with an annual loss of 1.7 trees per ha (Cannonizado and Hossain 1998).

Table 2: Comparison of the number of trees per ha in the SRF

E. agallocha is the second most important timber resources of the Sundarbans in terms of abundance, distribution, and commercial value. Similarly E. agallocha has reduced from 345 trees per ha found in the year 1959 (10 cm dbh and above) to 231 trees per ha in the year 1996. For E. agallocha 10cm dbh and above, the reduction in the number of trees between the Forestal and ODA inventories is 35 percent. Between ODA and FRMP inventories, the growing stock seems to have increased by 3.1 percent. Thus the decline in the number of trees per ha occurred only between 1959 and 1983. However, for E. agallocha trees 15 cm and above in dbh, the situation is quite alarming. The annual reduction over the 37 years between the Forestal and FRMP inventories is 1.14 trees per year. Between ODA and FRMP inventories, the reduction rate is 44.1 percent with an annual loss of 1.15 trees per ha.

The total volume and volume/ha of important timber species is known from the ODA inventory of 1983 (ODA 1985) and FRMP inventory of 1996 (Canonizado and Hossain 1998). The volume/ha of H. fomes, E. agallocha, A. officinalis and S. apetala found in ODA and FRMP inventory is given in Table 3. The volume/ha of H. fomes, E. agallocha, A. officinalis and S. apetala were 15.7 cu m/ha, 4.3 cu m/ha, 3.1 cu m/ha and 1.1 cu m/ha respectively in ODA and 17.76 cu m/ha, 2.12 cu m/ha, 2.21 cu m/ha and 2.09 cu m/ha respectively in FRMP inventory. There was a slight increase in the volume/ha of H. fomes and S. apetala and decrease in the volume/ha for E. agallocha and A. officinalis in FRMP inventory than the ODA one. The volume/ha for both the inventories were calculated on the basis of 15+ cm dbh. The volume/ha of H. fomes and S. apetala have increased due to the imposition of moratorium on the harvest of forest produce from the Government owned natural forest since 1985. The volume/ha E. agallocha and A. officinalis have decreased due to the reason of continued extraction for industrial and domestic use. It was found from the ODA and FRMP inventories that the total volume (15+ cm dbh) has decreased much in case of E. agallocha in comparison to H. fomes, which has also decreased to a certain extent (Canonizado and Hossain 1998), which was shown in Table 4. As a result, it is known that the tree resources of the SRF are decreasing due to the continuous harvest of produce.

Table 3: Volume/ha of timbers in the SRF found in ODA and FRMP Inventory

Table 4: Comparison and Change on the Volume of timbers of SRF

It is known that Tk. 31 450 (US$ 542) and Tk. 12 800 (US$ 220) (Tk. 58 = 1US$) is spent to establish per ha Enrichment plantation and ANR respectively. The Enrichment plantations are maintained for a period of 2 years and costs Tk. 3 960 (US$ 68) per year. It is estimated that the direct investment per ha of Enrichment plantation and ANR is US$ 678 and US$ 220 respectively. It is known that tree stock per ha will be increased by many times in the Enrichment plantation and ANR with the investment of aforesaid money. As a result the benefit is much higher in comparison to the cost of TSIs over a period of time. This TSIs are at the initial stage of implementation and it is assumed that the cost benefit ration could be ascertained after some time.

Moreover, it is found from the growth data that the present treatment of Enrichment planting and ANR is very much effective in terms of growth, survivability, and cost than the previous methods.

Conclusion

The tree resource and biodiversity of the SRF has decreased due to continuous harvest over a long period of time, where regeneration and survivability of the seedlings were totally dependent on the natural process. About one third of the forest have very much low crown cover either infested with climbers and bushes or barren with low scrub forest dominated by C. decandra. TSI treatments found very effective, which could increase the tree resource upto 400 trees per ha in course of time over one third area of the SRF.

Literature cited

Anon. 2000. Inception Report of the Sundarbans Biodiversity Conservation Project. Vol. I. Arcadis Euroconsult. Dhaka, 129 p.

Benthem, W., 2001. Update of TSI Interventions in 2001 and 2002.Technical Reports TR No. 08. ADB:Ban 1643/3158. Forest Department, Government of Bangladesh. Dhaka, 32 p.

Canonizado, J.A. and Md. A. Hossain, 1998. Integrated Forest Management Plan for the Sundarbans Reserved Forest. Vol. I. Mandala Agricultural Development Corporation and Forest Department. Dhaka. Bangladesh, I-72 p.

Curtis, S.J., 1933. Working Plan for the Forest of the Sundarbans Division Vol. I. Government of Bengal. Bengal Government Press. Calcutta, India, 175 p.

Gani, M.O., 2000. Occurrence and propagation of Bruguiera parviflora in the Sundarbans Mangrove Forest of Bangladesh. Bangladesh Journal of Forest Science. Vol.29(2): 139-140.

Heinig, R.L., 1892. Working Plan of the Sundarbans Government Forests. Government of Bengal. Bengal Government Press. Calcutta, India, 25 p.

Karim, A., 1995. Report on Mangrove Silviculture. Integrated Resource Development of the Sundarbans Reserved Forest. Vol. I. FAO/UNDP Project BGD/84/056. Khulna, 148 p.

Overseas Development Agency 1985. A Forest Inventory of the Sundarbans, Bangladesh Main Report. Land Resource Development Centres, Surbiton, England. 120 p.

Prain, O., 1903. The flora of Sundarbans. Records of the Botanical Survey of India. 144: 231-272.

Sattar, M.A. and M. Faizuddin, 1998. Biodiversity of the Sundarbans Mangrove Forest of Bangladesh and its Conservation. Bangladesh Journal of Forest Science. Vol.27(2): 71-75.