The historical background to invasions in the Mediterranean Basin is an integral part of the evolution of the region's natural and cultural landscapes. Vegetation changes were induced by a combination of climatic stress, natural and constant human disturbances and a resulting resilience to invasion. Recently, the problems of human impact on Mediterranean vegetation have been discussed in detail (see, e.g. Le Houérou, 1981; Pignatti, 1983; Pons & Quézel, 1985; Vernet & Thiébault, 1987; Naveh & Kutiel, 1990). In this chapter we shall describe, briefly, the natural and cultural processes which shaped the Mediterranean landscapes from the Pleistocene onwards. We shall then present some of the archaeobotanical evidence for evolutionary and historical changes in the vegetation.

The evolution of natural and semi-natural Mediterranean landscapes in the Pleistocene

The landscapes of the Mediterranean Basin are relatively young geological systems; they gained their present geomorphological forms by violent uplift in the late Tertiary and early Quaternary periods (di Castri & Mooney, 1973; di Castri et al., 1981). Final shaping of the landscapes took place in the Pleistocene in a highly dynamic period of climatic fluctuations, and tectonic and volcanic activity. Site conditions, both physical and biological, diversified increasingly. From the Middle Pleistocene onwards, early Mediterranean peoples further diversified these landscapes on both a regional and local scale, thereby contributing to their present multi-dimensional heterogeneity (di Castri, 1981).