VARIATIONS IN STOMATAL DENSITY AND INDEX - IMPLICATIONS FOR PALEOCLIMATIC RECONSTRUCTIONS

The variation in stomatal characters in leaves from one Alnus glutinos a (L.) Gaertn. tree is analysed, Measurements were taken from over 70 sites on the abaxial surfaces of representative 'sun' and 'shade' leav es having the same insertion point, The mean values of stomatal densit y and index in the shade leaf were significantly lower (71 and 93%, re spectively) than those for the sun leaf, Within leaves, up to 2 . 5-fo ld differences in stomatal density values were observed, Contour maps derived from the data reveal non-random trends over the leaf surface, Correlations between stomatal density, epidermal cell density and stom atal index indicate that the variation in stomatal density within leav es arose primarily from local differences in stomatal differentiation, rather than from local differences in leaf expansion, This research d emonstrates that a high level of variation in stomatal characters occu rs both within and between leaves, We conclude that a well-defined sam pling strategy should be used when estimating stomatal characters for (tree) leaves, Furthermore, the leaf's insertion point and situation w ithin the tree crown should be taken into account, We discuss the impl ications of these findings for palaeoclimatic interpretations and emph asize the need for great caution when drawing conclusions based solely on stomatal characters.