Effects of drought acclimation on the mechanical properties of Ochroma pyramidale, Betula pendula and Acacia karroo tree seedling stems

In all three species, individuals grown under drought conditions had on average stiffer and stronger stems than the well-watered individuals, though non-significantly so in A. karroo. These differences were associated with a higher density in O. Pyramidale but not in the other species. In B. pendula, the differences in mechanical properties appear to be associated with other factors, e.g. modifications of the micro fibril angle in the S2 cell wall layer. Our results indicate that drought acclimation in seedlings affects the mechanical properties of the stem but that the causal acclimational processes may vary between species.