The relationship between stem biomechanics and wood density is modified by rainfall in 32 Australian woody plant species

Stem mechanical properties are critically linked to foliage deployment and growth strategy, yet variation in stem mechanics across species and habitats is poorly understood. Here, we compared 32 plant species growing across four sites of contrasting rainfall and soil nutrient availability in Australia. The modulus of elasticity (MOE) and modulus of rupture (MOR) were tightly correlated with dry sapwood density within sites, but species from low-rainfall environments had higher wood density for a given MOE and MOR compared with species growing in high-rainfall environments. The ratio of MOE to MOR was slightly lower for species at low-rainfall sites, suggesting that wood was stronger for a given elasticity. Most species had thick bark, but the mechanical contribution of bark to stem MOE was small. Our results suggest that arid-adapted species would need to deploy more dry mass to support stems. Our results also highlight the importance of understanding how the biomechanics-wood density relationship evolves under different environmental conditions to better understand plant growth across diverse habitats.