A Quantitative Analysis of Leaf Form in Woody Plants from the World's Major Broadleaved Forest Types

The results of a compilation and analysis of pub- lished data on average leaf characteristics from multi-species samples of the world's major broadleaved woody vegetation types are presented. Highly significant linear regressions indi- cate several important trends across the major forest types. As lamina thickness increases, outer epidermal wall and cuticle thickness increases and specific leaf area (SLA) decreases. Thick leaves tend to have a lower thickness ratio of palisade to non-palisade mesophyll. Foliar concentrations of nitrogen (N) and phosphorus (P) are closely correlated with SLA. Crude fibre concentration and sclerophylly index (crude fibre/ crude protein) exhibit similar non-linear trends with leaf P concentration, the latter being governed by a negative expo- nential relationship where the degree of sclerophylly increases rapidly below 0.1% P. Together these represent a trend of increasing sclerophylly, a convergence point in leaf design shared by diverse vegetation types including Mediterranean shrublands, tropical heaths and tropical upper montane forests. The analysis shows that there is considerable variation both within and between vegetation types in leaf form. It does not satisfactorily distinguish any major groups within the sclero- phyllous communities. Further studies of community leaf form are required before we can have a quantitative understanding of these biogeographically important variables.