Variation in Leaf Size with Respect to Climate in Costa Rica

Abstract

Leaf-size variation with respect to climate was studied at 38 sample sites in Costa Rica. The variation in leaf size was analyzed by plotting the sample sites on Holdridge's (1967) life zone chart and comparing the percentage of species having large leaves (greater than 20.25 sq cm in area) in the different life zones. Three foliar belts could be identified in the tropical basal and altitudinal belts. Although the percentage of species having large leaves is significantly different between the foliar belts, the variation in leaf size is not continuous along environmental gradients either within or between foliar belts. The variation in leaf size within each foliar belt recognized suggests that other environmental parameters also have an important influence on leaf size. Extreme care must be exercised in the estimation of paleoclimate by angiosperm paleobotanists because of the potential variation in leaf size within a single foliar belt and the recognition that this variation does not follow climatic gradients. A CORRELATION BETWEEN LEAF SIZE distribution and climate in individual plant communities was first postulated by Raunkiaer (1934). He emphasized the effect of precipitation on leaf area. As precipitation decreased, the average leaf area in a flora also decreased. The percentage of species having large leaves should be greatest in the tropical lowlands with a net decrease in leaf area being noted when moving into drier environments. Temperature, the second major climatic variable recognized by ecologists (e.g., Holdridge 1967, Holdridge et al. 1971), was not emphasized in relation to leaf size because Raunkiaer (1934) felt that region-specific effects attributable to temperature either did not occur or could not be recognized. When analyzing the distribution of species having large leaves from around the world, Dilcher (1973) pointed out that plants do not respond to single climatic variables but to the total environment. For this reason, Dilcher attempted to correlate leaf-size distribution with both temperature and pre-