Surface growth stress and wood properties of 8-year-old planted Big-leaf mahogany (Swietenia macrophylla King) from different landrace provenances and trial sites in the Philippines

The scarcity of timber to supply the wood-based industries is one of the prevailing problems worldwide. Tree plantations are the remaining solutions to subdue the shortage of raw materials, at the same time sequester atmospheric CO2 in its biomass to reduce global warming. Planting Big-leaf mahogany (Swietenia macrophylla King) contributes valuable economic inputs to small tree farmers in the Philippines. However, the occurrence of lumber defects during processing due to growth stresses reduces the potential value of timber. This study aimed to examine the differences of surface growth stresses and wood properties of an 8-year-old BL mahogany from six landrace provenances in two progeny trial sites, Butuan and Cagayan de Oro in the Philippines. The longitudinal released strains of the surface growth stress (SRS) were not significantly different among six landrace provenances and between two trial sites. The SRS were not significantly related to diameter at breast height (DBH) in both trial sites. The high level of negative SRS was observed in some tested trees with small diameter in both trial sites, which was attributed to the tension wood formation in an irregular-shaped stem. The xylem density (XD), average microfibril angle in the secondary cell wall (MFA), vessel element length (VL) and vessel element width (VW) had no significant differences among six landrace provenances. In terms of trial sites, Butuan trial site gave high lateral growth DBH, high XD, longer fiber length (FL) with a narrow fiber width (FW) and smaller MFA as compared to the Cagayan de Oro trial site. It was observed that an 8-year-old BL mahogany plantation with small-diameter trees exhibited high SRS, low XD, small FL, wide FW and large MFA, which are passively considered as properties of juvenile wood.