Tropentag, October 6 - 8, 2009 in Hamburg "Biophysical and Socio-economic Frame Conditions for the Sustainable Management of Natural Resources"

Promoting Utilisation of two Light Broad-leaved Lesser-used Timber Species

Georg-August Universität Göttingen, Department of Wood Biology and Wood Products, Germany

Abstract

Myanmar has been practising a selective logging system since 1856, which has creamed forests for years, resulting in dwindling growing stock of commercial timbers. With scarcity of such valuable species and ever increasing timber demand, teak has been intensively planted throughout Myanmar to meet local requirements. Teak plantation has, however, deleteriously affected site quality and productivity, which impedes sustainable development of teak.

On the other hand, there still exist many lesser-used timber species in extensive forests of Myanmar. Augmenting demand for lesser-used species will lead to sustainable forest management. Two timber species Bombax ceiba and Bombax insigne characterised by their abundance and rapid growth occur throughout Myanmar and are economically and ecologically important for their flosses and conspicuous flowers. Bombax ceiba is superior to teak in its flourishing growth in dry areas and will become one of the most important species in rehabilitating central dry zones of Myanmar. However, their timbers are presently under-utilised.

To promote their utilisation, physical and mechanical properties of these timbers at green and 12% moisture content (MC) were investigated as basic requirements to marketing feasibility. Both species shrink on average by 2% in radial and 5% in tangential direction from green to oven-dry condition. Bombax ceiba swells by 2.3% (radial) and 5.7% (tangential), and Bombax insigne by 3.6% (radial) and 7.0% (tangential) from oven-dry to water-saturated condition. Their MCs are very high as measured after soaking in water. With modulus of rupture (MOR) of 28 N/mm², modulus of elasticity (MOE) of 4018 N/mm², maximum crushing strength (MCS) of 15 N/mm² at 12% MC and basic specific gravity of 0.23, Bombax ceiba is best suited to production of wood composites. Bombax insigne is also a light timber with basic specific gravity of 0.33. Its MOR is 60 N/mm², MOE 6880 N/mm² and MCS 28 N/mm² at 12% moisture content. It is strong enough to use in window and door frames, siding and furniture. Both timbers are nondurable, but their service life can be extended through environmentally friendly modification processes like impregnation with melamine resins, which also results in longer carbon storage as well.

Keywords: Basic specific gravity, mechanical properties, moisture content, shrinkage, swelling

Contact Address: Khin Maung Sint, Georg-August Universität Göttingen, Department of Wood Biology and Wood Products, Büsgenweg 4, 37077 Göttingen, Germany, e-mail: ksintgwdg.de