Cryptomeria japonica from Reunion Island: natural durability against basidiomycete fungi and termites, and contributions of near infrared spectroscopy to the prediction of its characteristics

Abstract

Cryptomeria (Cryptomeria japonica) is the only local timber species that can be used for construction on La Réunion. However, its variable durability against basidiomycetes fungi and termites is an obstacle to its use locally, since the island’s climatic conditions are particularly favourable to the degradation of bio-based materials.

This research consisted of accurately determining the natural durability of Cryptomeria wood against two ubiquitous basidiomycetes fungi (Rhodonia placenta and Coniophora puteana) and two termite species (Coptotermes gestroi from La Réunion and Reticulitermes flavipes from mainland France), using a very large sample. For benchmarking purposes, Scots pine (slightly durable), Red Cedar (durable) and Cryptomeria cladding were tested under the same conditions, leached or not, after 7 years of exposure to xylophagous organisms in La Réunion, in accordance with current European standard protocols. In addition, near infrared spectroscopy, coupled with chemometrics, was used to predict durability against basidiomycetes fungi.

The results confirm Cryptomeria susceptibility to termites and the very high variability of its durability against fungi. This species cannot be classified according to the classification principles for the EN 350 (2016) standard because the mass loss values (due to fungal decay) are distributed across the 5 durability classes, which range from "very durable" to "not durable".

Leaching and natural ageing give a better overall view of Cryptomeria performance, classifying it as "slightly durable to non-durable". Leaching has no influence on the performance of Red Cedar and Scots Pine, which remain classified as "durable" and "slightly durable", respectively.

Near infrared spectroscopy proved to be effective in predicting the natural durability of these species against fungi. Given the robustness of the model developed, this is a predictive tool that can help to optimise the use of Cryptomeria by enabling non-destructive assessment of the durability of its timber to ensure optimum performance, in France’s tropical overseas areas in particular.