What Is the ‘True’ Mediterranean-Type Vegetation?

Abstract

It has been demonstrated that evergreen sclerophylls are not always well adapted to, and do not flourish in, strongly winter-wet summer-dry climates [Blumler (Warm-temperate deciduous forests. Springer, 2015); Blumler and Plummer (Warm-temperate deciduous forests. Springer, 2015)]. What vegetation then is best adapted to mediterranean climates? Therophytes may be natural competitive dominants where soil is fertile, summer drought is protracted and extreme, and precipitation is low enough that it does not percolate downward significantly. Fertility matters because of its influence on the seasonality of the water regime (i.e., the “mediterraneanness” of the water regime, in a sense). Empirical data, collected originally by Raunkiaer but reinforced by more recent studies, suggest a greater tendency of annuals to flourish in seasonally dry than in arid environments. Studies of vegetation dynamics indicate that annuals can be highly competitive and perhaps even “climax” where winters are wet (but not too wet), and summers are hot, long, and dry. Tall, laterally expanding clonal plants of the sort that Grime classifies as competitors, do not thrive under such conditions, being largely restricted to mesic habitats where the seasonal drought is moderated. This leaves Grime’s competitive-ruderals, tall annual plants, as the most competitive species present in open habitats. Biome modeling and vegetation mapping would improve if the assumption of one biome per climate were relaxed and instead different life forms or functional types were mapped as overlays in a GIS.