Effects of heartwood extractives on mechanical properties of larch

The genus Larix is exceptional for its high content of extractives in the heartwood, with the dominant component arabinogalactan found abundantly in cell lumens of tracheids. On parallel samples prepared from 20 European, Japanese and hybrid larch trees (Larix decidua Mill., L. kaempferi Carr., and L. decidua x L. kaempferi, respectively) extractive contents and mechanical parameters were measured. The hot-water extractives in the heartwood had a significant effect on transversal compression strength and Young's Modulus. In heartwood, increasing extractive content went hand-in-hand with better mechanical properties in the transverse direction. The extraction procedure led to negligible changes in the sapwood. Anatomically the extractive-tilled tracheids showed a tendency of being arranged radially, closely to wood rays. The extractive arabinogalactan in larch heartwood has multiple effects on different aspects of wood quality, among which is lateral mechanical enforcement.