Low Temperature Effects on Mediterranean Sclerophylls: An Unconventional Viewpoint

Abstract

Mediterranean sclerophyllous trees and shrubs are considered to represent a life form which, by evolution and natural selection, has adapted to climates with summer drought and wet, mild winters. Obviously drought stress proves to be the climatic factor essentially responsible for the restriction of productivity, growth, and survival of evergreen woody plants in Mediterranean-type regions. In addition, low temperature effects in marginal districts, particularly in the northern and eastern parts of the Mediterranean basin and near to the altitudinal limit of the maquis vegetation, should not be neglected. Such effects are frost damage during severe winters, which are to be expected every 10–12 years (Morettini 1961), as well as reduced dry matter production and decreased vigour of the plants due to the depression of metabolic activities by suboptimal temperatures in December and January (Killian 1933, Larcher 1961a,b,1969a,b, Eckardt et al. 1975, Weinmann, Kreeb 1975). Recently the significance of low winter temperatures and episodic frost in limiting distribution range and causing alterations in the floristic composition of the maquis vegetation in Europe has been emphasized by Larcher (1980a) and Mitrakos (1980). Experimental data from previous investigations are evaluated here to illustrate the view that low temperatures, which were a major stress factor during Pleistocene, still exert a considerable influence on survival, reproduction and productivity of Mediterranean evergreen woody plants.