Relationships between sclerophylly, leaf biomechanical properties and leafanatomy in some Australian heath and forest species

A previous study of 19 south-east Australian heath and forest species with a range of leaf textures showed that they varied considerably in leaf biome chanical properties. By using an index of sclerophylly derived from botanis ts' rankings (botanists' sclerophylly index, BSI) we determined that leaves considered by botanists to be sclerophyllous generally had both high stren gth and work to fracture (particularly in punching and tearing tests), both at the level of leaf and per unit leaf thickness. In the current study we have shown that leaves from the same species also varied considerably in le af specific mass 146-251 g m(-2)), neutral detergent fibre concentration (2 0-59% on a dry weight basis) and in leaf anatomy. Multiple regression indic ated a very strong correlation between BSI and the first two components of a principal components analysis (PCA) of leaf anatomy (R-2 = 0.91). In addi tion, there was strong correlation between the first component of a PCA of the mechanical properties (correlated with BSI) and the two axes derived fr om anatomical characteristics (R-2 = 0.66). The anatomical properties contr ibuting most to the cuticle (axis 1) and percentage fibre (neutral detergen t fibre) and lower epidermis thickness (axis 2). However, whether these rel ationships are causal, or reflect correlations with characteristics not mea sured in this study, such as: vascularization and sclerification, is not cl ear. At a finer scale, however, there is evidence that there are various wa ys to be sclerophyllous, both in terms of anatomical and mechanical propert ies. This is illustrated by comparison of two of the sclerophyllous species , Eucalyptus baxteri and Banksia marginata.