Dry mass costs of deploying leaf area in relation to leaf size

Summary1 The leaf size–twig size spectrum is an important spectrum of variation between species, although the costs and benefits of larger vs smaller leaf size are poorly understood. This study quantified the dry mass costs of deploying leaf area in relation to leaf size, across 70 species from four sites contrasted on the basis of rainfall and soil nutrients in east‐temperate Australia. 2 Leaf mass fraction beyond 10 mm 2 of conductive cross‐section (LMF 10 ) varied threefold and was strongly positively correlated with leaf size, both across all species and within each habitat. This and other key correlations were significant both across species and as evolutionary divergences. 3 An LMF 10 advantage for larger‐leaved species should translate into a proportional advantage in dry mass acquisition, yet species with small leaves persist and sustain populations. This raises the question as to what factors might counterbalance an LMF advantage associated with larger leaf size. 4 Within some sites, specific leaf area (SLA) decreased with leaf size, which counterbalanced the LMF 10 advantage. Within other sites, and across all sites, SLA did not decline with leaf size. In these comparisons other factors, such as avoidance of overheating, must counterbalance the LMF 10 advantage to larger‐leaved species. 5 Wood density was negatively correlated with leaf size. However, the relationship was weaker within sites in the lower rainfall zone, and species in these sites had generally higher wood density. Sapwood cross‐sectional area per unit leaf area (Huber value) varied approximately ninefold across all species, and was correlated with both leaf size and SLA across all species, but not within sites.