A SURVEY ON THE DIE-BACK DALBERGIA SISSOO IN NEPAL

K. P. Acharya and N. Subedi
Department of Forest Research and Survey, Babarmahal, Kathmandu, Nepal

1. INTRODUCTION

Dalbergia sissoo (sissoo) is a riverine species found widely distributed in the natural forests of Nepal. Of recent, the species has become very popular with Government agencies and private tree growers giving its cultivation a very high priority. It has been widely planted in government, community and private lands, and in all localities. Growers in Nepal. This resulted from the high financial return estimated for the plantations. The plantations were promoted without considering the risks involved in such monocultures, and where no attention is paid to the quality of the planting material and the site selection. It has been estimated that around 90 % of the plantations in the Nepal terai come from this single species. Of recent, these the plantations have been suffering from a serious die-back diseases (Parajuli et al. 1999, FORESC 1998).

A few studies on the die-back disease have been recently completed (e.g. Parajuli et al. 1999, FORESC 1998) by the Department of Forest Research and Survey (DFRS). However, these studies were conducted only on few districts of Eastern and Central Region. Realising the significance of the problem, the DFRS has undertaken a national level research on the problem and the control measures. This 3 year project involves the assessment of the die-back damage in the first year. The survey was completed on all the 24 Terai districts, but here we provide the analysis of 3 terai districts each from the Eastern and Western Development Regions. The objective of the survey was to quantify the extent of damages of sissoo in plantations and in natural stands.

2. METHODOLOGY

The survey was carried out from 28 March to 19 April, 2000. The first stage was to acquire information on sissoo distribution in the districts. The sites were selected to represent different categories of sissoo stands, viz. Private, community and government owned and managed stands. Within these management regimes, various site categories such as river-side, degraded forest, natural stands, canal side, road side, and enrichment plantations were selected for the survey.

Out of the 178 sissoo stands in the three chosen districts in the Western Development Region, 26 were sampled among the government-managed and community-managed categories. Similarly, out of the 127 sissoo stands in the three districts from the Eastern region, 33 were sampled. There were 154 registered private plantations in Nawalparasi, 70 in Rupandehi and 20 in Kapilvastu districts, out of which 20 were assessed. Similarly, out of the 486 private registered plantations, 30 were sampled in the Eastern Development Region.

In addition to the field survey, Participatory Rapid Appraisal (PRA) tools such as key informant's interview, group discussion, and transect survey were carried out to obtain information on die-back phenomenon and the impact of the die-back on the planters.

3. RESULTS

3.1. Sissoo Population

Information on the sissoo population was provided by the respective District Forest Offices in the six study districts (Table 1).

Table 1. Area of sissoo stands in six districts of the study areas.

3.2. Extent of Damage

Western Region

Sissoo plantations of various sizes, age, type of sites and localities have been found affected by the disease. The riverine plantation sites were least affected and one natural stand was not affected by the disease compare to other plantation sites. In the Region, 19 % of sissoo trees in government-managed and community-managed stands have been affected by the disease, and 7.3 % of the standing trees were dead. A total of 19 % of trees on private land were dying while 13 % had died. The summary is given in Annex 1.

Eastern Region

In the Eastern Region, 16.58 % of sissoo trees in government managed and community managed stands were affected by the disease, and 2.99 percent of the standing trees were dead. A total of 0.73 percent of trees on private land were dying while 9.82 % had died. The summary is given in Annex 2.

4. DISCUSSION

Sissoo seems to prefer alluvial, well-drained soil along riverine sites. The condition of the plantations differed from the natural stands. Plantations need several silvicultural operations to ensure their performance is good. This was neglected, creating favourable conditions for pests and disease. The spread of the disease in the few riverine sites and natural stands was not significant in western region, indicating the sites were suitable for sissoo. The plantations were not all located in such sites, explaining for the high disease incidence in them. Other contributing factors could be seed source and its quality, raising of seedlings, and plantation preparation techniques. However, riverine plantations with sandy soil and water logged conditions were also affected. No single patch of plantation stand studied in the selected districts has remained unaffected by the disease.

The tree can die within a couple of weeks following appearance of the sign, drying of the branches from the top downwards. In a tree, while a few branches are drying up, others are still green. The top branches may die, and the downward progress may stop. Some of the cut stumps have coppiced profusely. The incidence of the disease was higher in mature and over-mature trees compared to young trees.

At present the disease appears to be spreading very fast. In the western region the disease was noticed four years ago, and is now affecting almost 25 % of the trees (The estimation will fluctuate depending on the number of trees that have already died and were excluded from the survey.).

5. CONCLUSIONS

The die-back of Dalbergia sissoo is widespread in the terai region of Nepal. It is causing much economic loss and an unfavourable environment for the tree growers. Firstly, the sudden excessive supply of sissoo wood due to removal of the large number of dead and dying trees is lowering the price. Next, the utilisation of such diseased trees is not well known either.

6. REFERENCES

Parajuli, A.V., Bhatta, B., Adhikari, M. K., Tuladhar, J. & Thapa, H. B. 1999. Causal agents responsible for the die-back of Dalbergia sissoo in Nepal's eastern Terai, Banko Janakari 9(1).

FORESC. 1998. A Report on Field Investigation of Top-dying of D. Sissoo Growing at Some Districts of the Central and Eastern Terai. Forest Research and Survey Centre, Kathmandu.

Annex 1. Summary of disease incidence of sissoo in government and private plantations in Western Development Region

A) Government and community controlled stands

B) Private Plantations

Annex 2. Summary of disease incidence of sissoo government and private plantations in Eastern Development Region

1. Government and community controlled stands

B) Private Plantations