M.W. Baksha and A.C. Basak
Bangladesh Forest Research Institute, P.O. Box 273, Chittagong 4000,
Bangladesh
Bangladesh, with high population density, have been facing a serious crisis for timber and fuel wood. Public forest land is only about 16% of the total land area of the country, of which only 6.5% is under actual tree cover. The present annual round wood supply in the country is estimated to be 7.9 million m3 as against the demand of 13.6 million m3. The gap will widen further in the future due to ever-increasing population pressure. To meet the demand for timber and fuelwood, and to stop further ecological degradation, the Government Forest Department, NGOs, private planters and general public have actively initiated tree planting in the denuded forest areas, in the homesteads, along rail, roads and highways, on embankments, in marginal and wastelands and even in the crop fields. Sissoo (Dalbergia sissoo Roxb.), being a multipurpose tree species, has been a valuable planting species for afforestation, industrial plantation and farm forestry. According to FAO (1988) study, 9.7 million ha of flood plain soil in north and south-western districts is the most suitable land for growing Sissoo.
No timber species except teak is so extensively planted as Sissoo in the country. The species is commonly planted in community forests, private forests and wood lot plantations and in the homestead, though the exact area covered by this species has not been ascertained. However, it is assumed that about 60% of the plantations in north and southern, 40% in the central and northern and 20% in the eastern hilly areas are planted with D. sissoo.
In block plantations, D. sissoo is raised in pure stand, while in other types of plantations it is planted as pure or mixed stand (with S. macrophylla, Acacia nilotica, Arjun, Melia azadirach, etc.).
Mortality of D. sissoo has been observed during the last few years. Press and public interests highlighted concern over the future of D. sissoo plantations (Anonymous 1997, 1998). Trees of varying ages right from sapling to mature trees were found to be affected. The mortality usually occurs during the humid months from July to September.
The characteristic symptoms are yellowing and death of leaves in acropetal succession up the trees, as a result, the whole tree appears yellow. In advance stages the leaves shed rendering the branches bare, the affected trees show signs of wilting and ultimately die within a few months. Older trees are usually found to be more prone to mortality . The outer sapwood shows characteristic pink to reddish stain. Though this is restricted to outer sapwood, it sometimes penetrates in the inner sapwood, the heartwood is not discoloured. The stain progresses along the outer sapwood of the root to the stem and in later stages of wilting it extended up the stem to about 3-5m from the ground.
Signs of small insect boring were observed on the bark of the weakened or dying trees. Stains of oozing sap from the entrance holes made by the insects are characteristic symptoms.
The symptoms of the die back and subsequent mortality may be due in part to the fungus Fusarium solani (Mart.) Appel & Wr., which is facultative parasite inhabiting soil and which is capable of saprophytic colonization (Bakshi 1955). The boring on the bark and wood was caused by the shothole borer, Euplatypus sp. (Coleoptera: Platypodidae). The attack of this insect appears to be secondary after the trees have become weakened by the fungal attack or by other physiological factors. However, the actual cause of mortality of D. sissoo still remains uncertain.
Mortality is mostly prevalent in the plantations of north and southern and central plains of Bangladesh. The most affected districts are Comilla (Basak 1994), Kushtia Chundanga, Jhenida, Jessore, Mymensingh, Pabna, Dinajpur, Rajshahi, Meherpur, Magura, Brahmanbaria and Natore (Fig. 1 WHERE IS FIGURE 1?). However, there is no report of mortality in woodlot plantations in the hilly areas.
No systematic survey has been conducted to assess the actual extent of mortality in D. sissoo. However, casual reports revealed the following:
|
Age of plantation (year) |
Reporting years |
Plantation type |
Affected area |
Magnitude of tree mortality |
|
2 |
1994 |
Comilla roadside plantation |
60% |
- |
|
3 |
1996 |
Jessore homestead private plantations |
60% |
40% |
|
2-3 |
1996 |
-do- |
50% |
- |
|
5 |
1996 |
Kustia roadside plantation |
- |
100-150 nos. |
|
15-20 |
1996 |
Darsona college campus |
- |
75% |
|
2-20 |
1997 |
Islamic University campus, Kustia |
- |
100 nos. |
|
5-8 |
1999 |
Fisheries Research Institute campus, Mymensingh |
- |
To address the problem of Sissoo mortality a small scale research study has been undertaken by the Bangladesh Forest Research Institute (BFRI), Chittagong which has limited funding, manpower and infrastructure facilities. These limitations were discussed at a high level meeting in the Ministry (Ministry of Environment and Forest). As per the suggestion of the meeting a Technical Assistance Project Proposal (TAPP) entitled, "Investigation on the cause of mortality of sissoo (Dalbergia sissoo Roxb.) and its control" was submitted to the Ministry in December, 1999 which is still awaiting suitable donor support and approval.
No research based remedial/preventive measures have been suggested to tackle the problem, as research is still in the initial stages. However, both chemical and non- chemical methods have been planned in the research proposal as part of an integrated pest management strategy. Meanwhile, based on experience some interim remedial/preventive measures have been suggested to the planters to help contain the problem. These include:
i) Application of Callixin @ 1 gm/l and Furadan (carbofuran) 3 G @ 50-100gm/plant as soil drench so that the chemical is able to leach down to the roots deep in the soil;
ii) Avoiding plantation of D. sissoo in monoculture;
iii) Uprooting dead and dying trees so that the breeding place of the fungus/insect is destroyed to stop further spread of the mortality;
iv) Planting D. sissoo in suitable sites (well-drained, sandy soil avoiding clayey water-logged soil).
In clayey soil the aeration is poor and the roots die of asphyxiation. Soil inhabiting fungi are able to infect the tree through dying or weakened roots (Bakshi 1957). It is probable that in the flood plain basin, where the water table is high and may come up to the surface due to heavy rain and flood, Sissoo is already stressed and is thus susceptible to wilt.
Sissoo mortality is one of the major national problems affecting afforestation in the country. High priority is given to deal with the problem. As mortality of D. sissoo is now a major problem in countries such as India, Bangladesh, Pakistan, Nepal where D. sissoo is planted extensively, a collaborative research study is urgently recommended. This is particularly important when selecting disease resistant provenances . It should be noted that in Bangladesh Sissoo seems to have a very narrow genetic base.
Anonymous 1997. Pest damage valuable trees on IU campus. The daily Independent, 3 November 1997, Dhaka.
Anonymous 1998. (Lacs of sissoo trees in 26 north and south western districts are dying form unknown diseases). The daily Banglabazar, 14 Poush, 1404, Dhaka.
Bakshi, B.K. 1997. Wilt disease of shisham (Dalbergia sissoo Roxb.). The effect of soil moisture on the growth and survival of Fusarium solani in the laboratory. Indian Forester 83: 505-511.
Bakshi, B.K. 1995. Wilt diseases of shisham (Dalbergia sissoo Roxb.) Behaviour of Furarium solani, the wilt organism in soil. Indian Forester 81: 276-281.
Basak. A.C. 1994. Wilting of sissoo (Dalbergia sissoo Roxb.) in strip plantations in Bangladesh. Bangladesh Journal of Forest Science 23(1): 67-68.
FAO, 1998. Agroecological regions of Bangladesh. Report 2, UNDP/FAO Project BGD/81/035, FAO, Rome. 569 pp.
