Determining teak durability in record time

The teak currently on the market primarily comes from plantations in some thirty tropical countries. In effect, while global demand is continuing to grow, the natural forests in which teak originated are disappearing or are now protected. However, the natural durability of plantation teak can vary substantially from one tree to another. While wood from natural forests is in durability class 1 (highly durable) or 2 (durable), in some cases, plantation teak varies between class 1 and class 4 (slightly durable)*.

Laboratory studies of teak natural durability take 40 weeks to produce results. Researchers from CIRAD and its partners have managed to overcome this constraint, and developed a method that takes just a few minutes. Their brainwave was to correlate the analysis of teak natural durability with the variability of its chemical composition as revealed by near-infrared spectroscopy.

The first step for the researchers was to collect several hundred teak samples from trees of different ages, primarily from Togo, Ghana, Ivory Coast, Malaysia and Burma. The natural durability of wood depends on the age of the tree, its environment (soil, climate, geographical origin) and its genome. It is also closely linked to the nature of the chemical constituents (terpene and phenolic compounds, etc) that give it its natural resistance. The wood preservation laboratory subsequently determined the durability class of the samples based on the loss of mass caused by exposing them to wood-eating fungi (Antrodia sp. and Coriolus versicolor). Lastly, the researchers correlated the loss of mass for each sample with its near-infrared absorbency.

The database they compiled makes it possible to predict the natural durability class of teak samples within a few minutes. The wood sample – a core sample around 1.5 cm in diameter – is sliced and placed in front of the “eye” of the spectrometer, providing data that can be analysed using the database, which now contains the characteristics of more than 5000 teak samples from some ten countries, taken from plantations aged between 5 and 40 years, and from natural forests. It will be supplemented regularly with new samples, particularly from Asia, South America and Central America, where teak is a boom crop. Broadening the range of samples will help to improve the accuracy of durability predictions. The database could also provide geneticists with a new tool for use in breeding improved teak varieties.

* The natural durability of wood with respect to various degrading agents is assessed based on a European standard (EN350-1). As regards wood-eating fungi, durability is ranked from class 1 (highly durable) to class 5 (non-durable).