Leaf size and leaf consistence of a riverine forest formation along a climatic gradient.

Abstract

The riverine forest formation on the levees along the Orange River in South Africa shows a shift in floristic composition as the river traverses various climatic zones on its course through the temperate area in the eastern parts of the subcontinent, the central semi-desert region, and the desert area near the Atlantic in the west. Leaf size classes and leaf consistency types of the woody species in the riverine forest were determined for each community. Analysis of these data revealed a diversification of leaf sizes as the climate changed from temperate to hot and arid and particularly microphylls became relatively less important and were replaced by smaller leaves in the hot areas. In the same direction malacophylls, which are of the "low-cost, quick-profit" strategy type and are well represented in the temperate, frosty areas, disappear and xeromorphic leaves ("high-cost, slow-profit" strategy type) increase in importance. It is suggested that the cooler conditions with higher wind speeds and higher degrees of average air humidity near the Atlantic coast are reflected by an increase in mesophylls which are sclerophyllous as an adaptation to the frequently and rapidly changing temperature conditions here.