Different strategies of drought resistance in three Mediterranean sclerophyllous trees growing in the same environmental conditions.

Measurements have been made of leaf conductance to water vapour, relative water content and water potential in Olea oleaster Hoffmgg et Link, Ceratonia siliqua L. and Laurus nobilis L., three evergreen sclerophyllous trees growing in Sicily at sea level. Measurements were made hourly in May and September 1986. Although all the three species are regarded as components of a homogeneous group (sclerophylls) and they all showed a high degree of sclerophylly, the strategies they adopted to withstand drought were completely different. Olea oleaster behaved as a 'drought-tolerating' species. Drought was 'avoided' by Ceratonia siliqua by a 'water-spending' strategy and by Laurus nobilis by a 'water-saving' strategy combined with the capability of recovering even minimal water losses by dropping leaf water potential drastically. Such differences in drought resistance are discussed in terms of differences in the bulk elastic modulus of leaf cells and wood anatomy.