Natural durability of a lesser-used tropical hardwood (Detarium microcarpum) under severe tropical in-ground exposure: Implications for sustainable substitution of overexploited timbers

Abstract

The overexploitation of naturally durable tropical hardwoods has intensified the search for lesser-used species capable of supporting sustainable timber utilisation. Evaluating wood performance under conditions of severe biological stress is essential for assessing their suitability for substitution in outdoor and ground-contact applications. This study investigated the natural durability of Detarium microcarpum , a lesser-used tropical hardwood, under severe tropical in-ground exposure characterised by high biological deterioration pressure. Wood stakes obtained from basal, middle, and upper axial stem positions of mature trees were exposed to soil contact for six months following the EN 252 field test protocol. Biological deterioration was quantified using percentage mass loss, and durability classes were assigned based on established classification criteria. Results revealed a clear axial trend in durability, with mass loss increasing significantly from the basal to the middle and upper stem sections (p < 0.05). Although all axial positions were classified as non-durable under the severe exposure conditions, basal stem material exhibited comparatively greater resistance to biological attack. This enhanced performance is attributed to higher heartwood proportion and associated protective extractives typically concentrated in lower stem regions. The findings demonstrate that severe tropical in-ground exposure provides a robust field-based system for evaluating wood durability under high biological deterioration pressure and highlight the importance of within-tree variation when assessing lesser-used hardwoods. While preservative treatment is required for ground-contact applications, D. microcarpum , particularly basal stem material, shows potential for sustainable substitution of overexploited commercial timbers in tropical forestry and wood utilisation systems.