Mediterranean weeds: exchanges of invasive plants between the five Mediterranean regions of the world

Abstract

The five regions of the world sharing a climate like that of the Mediterranean Basin have exchanged, and continue to exchange, weedy plant species. This exchange is seen to be of two forms: an earlier primary invasion of the other four regions by aggressive annual weeds from the Mediterranean Basin and a later secondary invasion by woody species, often between the four regions and from them back to the Mediterranean Basin. Of the woody invaders two interesting groups are the conifers and the succulents. There is also a tertiary invasion within each of the mediterranean regions of native species that have become more invasive as a result of human disturbance.The five regions are seen to comprise three groups. The pivotal ‘crossroads’ (di Castri 1981) of the Mediterranean Basin itself, the other more recent (Pleistocene) group of Chile and California, and the older (Gondwanan) group of South Africa and southern Australia. As well as sharing important evolutionary and biogeographic traits (Naveh & Whittaker 1980, di Castri 1981), the two subsidiary groups are seen as sharing important patterns of settlement and subsequent trade. California and Chile, as well as having other strong links with the Mediterranean Basin, were discovered and first settled by people from the Mediterranean Basin and this early contact must have dictated the rate and extent of invasions. The two older, southern regions, Australia and South Africa, on the other hand, were settled by people from northern Europe and only latterly had direct trade links with Mediterranean countries.The prognosis for the future of invasions in the mediterranean regions is for a reduction in agrestal weeds but an increase in community weeds, particularly woody secondary invasions.KeywordsMediterranean RegionMediterranean BasinBiological InvasionCape RegionMediterranean EcosystemThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.