Bambusa polymorpha (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Bambusa polymorpha Munro

Protologue: Trans. Linn. Soc. 26: 98 (1868).

Family: Gramineae

Chromosome number: 2n= 72 (hexaploid)

Vernacular names

• Burma (Myanmar): kyathaungwa
• Thailand: phai-hom (northern).

Origin and geographic distribution

B. polymorpha most probably originated from Burma (Myanmar); its natural range extends westward to eastern Bangladesh and eastward to northern Thailand. It is most important in Burma (Myanmar). Occasionally it is grown outside its natural area in botanical gardens or other collections (e.g. in Indonesia, India, United States, Puerto Rico).

Uses

Culms of B. polymorpha are used for construction (walls, floors, roofs), matting, handicrafts, paper- and board-making. The young shoots are edible but are reputed to taste very bitter.

Production and international trade

Production of B. polymorpha should be considerable in Burma (Myanmar) where it is the major source for bamboo constructions, and in Bangladesh where it is an important source for paperpulp and board, but no statistical data are available. Trade is mainly local.

Properties

From B. polymorpha culms, the following data have been reported: fibre length 2.4-2.5 mm, fibre diameter 16-23μm, lumen diameter 5-13μm, fibre wall thickness 5μm, density 619 kg/m³at moisture content 95% (green bamboo) and 659 kg/m³at moisture content 13.9% (air-dried bamboo); for green and air-dried culms the modulus of elasticity is 3070 N/mm²and 4315 N/mm²and the modulus of rupture 27.8 N/mm²and 34.8 N/mm²respectively; for green culms the compression strength parallel to grain is 31.5 N/mm². The chemical composition of the culms (oven dried) is approximately as follows: holocellulose 54-62%, pentosans 18-21%, lignin 21-22%, ash 1.7-1.8% (silica 0.3%); the solubility in cold water is 3-5%, in hot water 7%, in alcohol-benzene 1.7-1.9%, in 1% NaOH 18-22%.

From an analysis in Puerto Rico it has been reported that the edible portion of young shoots is about 18% and that the canning quality is good.

Description

Densely tufted, sympodial bamboo, sometimes deciduous. Culm erect, curving outward at the top, 15-25 m tall, 7.5-15 cm in diameter, wall 12-20 mm thick, with appressed white deciduous hairs and white wax when young, when older white-pruinose, bluish-to greyish-green; internodes 60-100 cm long; nodes thickened. Branches arising from nodes in upper half of the culm. Culm sheath 15-17.5 cm × 30-35 cm, thick, junction with blade distinctly upcurved towards middle, long persistent, with appressed white hairs on back; blade ovate-triangular, erect or slightly diverging, 12-15 cm long, strongly convex, green or purple, base decurrent band-like along apex of sheath, lower margins long ciliate, apex thorn-like, outside with appressed, white, deciduous hairs, inside glabrous; ligule 4-5 mm long, irregularly dentate, ciliate; auricles at first embracing the culm, later becoming obliquely erect, long ciliate. Leaf blade lanceolate or linear-lanceolate, 7.5-20 cm × 8-20 mm, slightly rough from minute tubercles, at first hairy on both surfaces; sheath compressed, slightly keeled at top, green; ligule very short; auricles 0.25-0.5 mm, ciliate. Inflorescence consisting of pseudospikelet groups born on long branches; pseudospikelet brownish, enclosed in a long curved glabrous bract; spikelet comprising 1-3 empty glumes and 2-3 florets. Caryopsis ovoid, 5 mm long, plano-convex with hairy top.

Growth and development

The life cycle of B. polymorpha is estimated at 60 years. It normally flowers gregariously during 2-3 years, after which the clump dies. A clump in the Botanic Garden of Bogor (Indonesia) flowered from 1970-1978. Natural regeneration is through seed, which is produced abundantly. A seedling needs more than 10 years to develop into a mature clump. In a mature clump the ratio new to old culms is about 1 to 4. In India some 6-year-old clumps, developed from rhizome cuttings, contained on average 80 culms that were 11 m tall and 17 cm in diameter.

Ecology

B. polymorpha is abundant throughout the more humid types of mixed deciduous forest in Burma (Myanmar), particularly on the lower slopes and in well-drained valleys. It flourishes best and reaches its largest dimensions on deep fertile loams. It is commonly associated with teak ( Tectona grandis L.f.) and is an indicator of deep, rich, well-drained soils on which teak also develops well. On such soils, B. polymorpha is often gregarious to a marked degree, frequently accompanied by Cephalostachyum pergracile Munro, a bamboo of almost equal importance but extending also into forests of a somewhat drier type than that in which B. polymorpha is characteristically found.

Propagation and planting

B. polymorpha can be propagated by seed, rhizome, branch and culm cuttings. Natural propagation is by seed. The weight of 1000 seeds is about 38 g. Germination percentage is about 40%. Seedlings are raised in a nursery and are usually transplanted to the field when about 30-50 cm tall. Seedlings may also be collected from natural stands, for planting out. Rhizome cuttings are preferably taken from 2-year-old culms; their survival rate is almost 100%. For larger plantations, rhizome cuttings are not practical because too many mother clumps have to be damaged. Branch cuttings, planted under humid conditions, have been successful in Bangladesh (90% success rate); induction of roots and rhizomes on branches still on the living plant had a 80% success rate. Whole culm cuttings have been quite successful in the United States: one or two-year-old whole culms produced about 3.5 new plants per 3 m culm, especially from middle and top parts; culms 3 years or older produced on average about 1 plant per 3 m culm. Culm cuttings (parts) are usually planted in the early rainy season, 7-15 cm deep in a rooting medium (e.g. coarse sand) and at a slant (about 45°with soil surface).

Planting in the field is done in holes of about 45 cm × 45 cm × 45 cm at distances 4 m × 4 m.

Husbandry

Regular weeding is necessary until the plants are well-established. Watering is needed when rainfall is insufficient. Application of farm manure or other fertilizer is very beneficial. B. polymorpha has a tendency to grow very densely, so thinning and removal of culm remnants promote culm and clump development.

Diseases and pests

No serious diseases or pests are known for B. polymorpha .

Harvesting

Harvesting of culms may start when clumps are more than 5 years old. Culms to be harvested should be older than 1.5 years; for construction purposes, 3-4-year-old culms are preferred. For a sustainable yield, at least 8-10 old culms should be left in the clump.

Yield

In a 10-year trial in Burma (Myanmar), 2 culms per clump were cut annually without a visible weakening effect for the clumps. For the paper industry in India, a yield of 22 t/ha of air-dried culms in a 3-year rotation has been reported for B. polymorpha .

Handling after harvest

The natural durability of B. polymorpha is poor. Untreated, exposed culms are destroyed within 19 months by termites, fungi and borers. Traditionally, harvested culms are submerged for 10-20 days in running water and air dried before being used. Green culms lose about 40% of their weight when air dried. Preservative treatments can be given before or after drying. For green bamboo good results are obtained by soaking whole or half-split culms in a hot creosote/fuel oil mixture (1 : 1) for 3-6 hours; for air-dried culms (whole or split) by soaking in a 5% copper-chrome-arsenic solution for 6-12 days.

Genetic resources and breeding

For B. polymorpha a small germplasm collection is maintained in India (Bambusetum Van Vigyan Kendra, Chessa, Arunachal Pradesh). More collections are needed from all areas of its natural distribution. No breeding programmes exist for B. polymorpha .

Prospects

B. polymorpha is a very useful bamboo and of major importance in rural areas of its natural range. To protect natural bamboo forests, proper harvesting regulations should be established. Research efforts should focus on properties to widen its utilization and on possibilities for large-scale cultivation inside and outside its natural range.

Literature

• Banik, R.L., 1984. Macro-propagation of bamboos by pre-rooted and pre-rhizomed branch cuttings. Bano Biggyan Patrika 13: 67-73.
• Huberman, M.A., 1959. Bamboo silviculture. Unasylva 13: 36-43.
• Kumar, S. & Dobriyal, 1990. Preservative treatment of bamboo for structural uses. In: Ramanuja Rao, I.V., Gnanaharan, R. & Sastry, C.B. (Editors): Bamboos current research. Proceedings of the international bamboo workshop, November 14-18, 1988, Cochin, India. The Kerala Forest Research Institute, India and International Development Research Centre, Canada. pp. 199-206.
• McClure, F.A., 1966. The bamboos, a fresh perspective. Harvard University Press, Cambridge, Massachusetts, United States. p. 232.
• Silviculture Division, 1993. Extension publication on reforestation [Thai]. Royal Forest Department, Bangkok. p. 318.
• Troup, R.S., 1921. The silviculture of Indian trees. Vol. 3. Oxford University Press, London. pp. 977-1013.
• Varmah, J.C. & Bahadur, K.N., 1980. Country report and status of research on bamboos in India. In: Lessard, G. & Chouinard, A. (Editors): Bamboo research in Asia. Proceedings of a workshop held in Singapore, 28-30 May 1980. International Development Research Centre, Ottawa, Canada and the International Union of Forestry Research Organizations, Vienna, Austria. pp. 19-46.

Authors

P.C.M. Jansen & S. Duriyaprapan