Natural durability and anatomical features of teak (Tectona grandis) from plantations in Costa Rica
IRG/WP 08-10671
U J Wolfsmayr, N Terziev, G Daniel
Teak (Tectona grandis) possesses superior mechanical properties and durability and is thus frequently used as an alternative to impregnated timber in Europe. Demand on teak has resulted in severe exploitation of the tropical teak forests in recent decades, but today the imported timber originates mainly from plantations and is certificated according to the Forest Stewardship Council (FSC) policy. The origin of teak is Asia, which is still the most important producer of teak timber coming from both natural forests and plantations. Teak has been planted successfully in Central America. Since the 90’s, an Austrian forest company owns and maintains teak plantations in Costa Rica. In general, teak is very durable (class 1 according to standard EN 350-2) and the objective of the present study was to investigate whether the durability of plantation timber was in line with that determined in the standard EN 350-2. Since the trees are young (15-year-old), the trunks consist entirely of juvenile wood and the proportion of sapwood in the raw material is high. Natural durability of plantation teak wood from Costa Rica was tested according to standard EN 113 by means of brown- and white rot fungi (Gloeophyllum trabeum, Postia placenta, Lentinus lepideus and Trametes versicolor). Localisation of extractives in fresh sap- and heartwood as well as the propagation of fungal decay were studied by light microscopy and various staining techniques. The samples originated from butt- and top logs in longitudinal direction and inner and outer heartwood and sapwood in radial direction. In contrast to studies that have shown decreased mechanical characteristics of plantation teak to naturally grown timber, the durability of juvenile teak timber was in line with that determined by the standard. No significant difference in durability was found between butt and top log samples. The plantation teak sapwood was classified as moderately durable (class 3) while the outer heartwood was very durable (class 1). Only the heartwood portion near to the pith was classified as durable (class 2). The white rot fungus Trametes versicolor caused the most severe mass loss in the range of 16-19% for sapwood samples and 2-3% for the outer heartwood. The study concluded that the heartwood of plantation teak timber from Costa Rica fulfils expectations regarding the durability of the material. An on-going study will complete the mechanical behaviour of plantation timber.
Keywords: decay fungi, EN 113, EN 350-2, extractives, microscopy, natural durability, plantation teak
Conference: 08-11-30/12-02 Flamingo Beach, Costa Rica