Abstract
2The five mediterranean-type climate (MTC) regions of the world, notable for their globally significant levels vascular plant diversity and endemism, fall into two groups. The Cape Region of South Africa and southwestern Australia are ancient and relatively climatically and tectonically stable landscapes with very high species richness relative to their area. This richness reflects a core of paleoendemic lineages as well as Neogene diversification. In contrast, California, the Mediterranean Basin, and central Chile are young climatically and tectonically dynamic landscapes that have developed significant floras in the Neogene. This relative pattern of species richness breaks down when only conifers are considered. Collectively the five MTC regions have a conifer flora of 122 species, almost 20% of the global total, and are rich in endemic conifers species. This diversity is heavily centered in California with 58 species (31 endemic) and the Mediterranean Basin with 40 species (32 endemic). The key to success of conifers in the Northern Hemisphere MTC regions has been the evolution of functional hydraulic traits associated with cold and/or drought tolerance, as exemplified by Neogene diversification in many clades of Pinaceae and Cupressaceae, and by ecophysiological traits that offer competitive advantages over angiosperms on oligotrophic soils. Podocarpaceae and many other Southern Hemisphere conifer lineages never developed equivalent traits and were poorly adapted to surviving increasingly cool and strongly seasonal climate regimes with associated aridity in the late Neogene. Because of extinctions, conifer lineages in the Southern Hemisphere today exhibit a significantly older distribution of divergence ages than their counterparts in the Northern Hemisphere and are home to many isolated relict taxa. This can be seen well in Chile and the Cape Region where there has been little or no Neogene diversification of conifers and a preponderance of relict Gondwanan lineages remain. Only Callitris in southwestern Australia among the Southern Hemisphere MTC floras has been able to evolve successful ecophysiological traits to adapt to aridity in a fire-prone environment and diversify. Traits of cold, drought, and low nutrient tolerance of Northern Hemisphere conifers, most notably in the Pinaceae, have led to their widespread introduction in Southern Hemisphere agroforestry
Highlights
The five mediterranean-type climate (MTC) regions of the world—California, the Mediterranean Basin, central Chile, the Cape Region of South Africa, and southwestern Australia— share the unusual climate regime of cool wet winters and warm dry summers (Figure 1)
Southern Hemisphere MTC regions? This paper presents an overview of patterns of diversity and endemism for conifer lineages within the five MTC regions and the role of increased Neogene seasonality and associated low temperature extremes and drought in influencing the modern conifer distribution and endemism in contrast to that exhibited by flowering plant species in these regions (Cowling et al, 1996; Rundel et al, 2016)
The presence of Cupressaceae in the Cape Region of South Africa is limited to three species of Widdringtonia, all shrubby trees that occasionally reach to heights of 10–20 m or more (Midgley et al, 1995; Pauw and Linder, 1997)
Summary
The five mediterranean-type climate (MTC) regions of the world—California, the Mediterranean Basin, central Chile, the Cape Region of South Africa, and southwestern Australia— share the unusual climate regime of cool wet winters and warm dry summers (Figure 1). The pattern of vascular plant species diversity for both the western and eastern Mediterranean Basin present lower and intermediate patterns of contemporary plant diversity, followed by California and the lowest species richness in central Chile (Cowling et al, 2015; Figure 2) These three regions represent younger landscapes with strong rates of Neogene diversification in flowering plants (Cowling et al, 2015; Rundel et al, 2016). What factors can explain the relatively low level of conifer diversity in the three
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