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Mediterranean- and tropical-climate regions harbour the richest regional-scale floras globally. Until recently, however, comparisons of their diversities have been hindered by a lack of comprehensive inventories of tropical floras. Using taxonomically verified floras, we analyse area-adjusted plant diversities of five Mediterranean- and 35 tropical-climate regions to determine which are the most species-rich regions on Earth. On average, the Neotropics and tropical Southeast Asia support the most diverse floras globally. However, the area-adjusted diversities of the richest floras in these tropical regions are matched by those of two Mediterranean-climate floras, namely the Cape (second richest) and Mediterranean Basin (sixth richest). Except for Madagascar and Burundi, the Afrotropical regions were substantially less diverse than other tropical floras and half of the Afrotropical floras were poorer than the least diverse Mediterranean-climate region, namely Central Chile. We evaluate the likely ecological and evolutionary drivers of these plant diversity patterns in terms of three hypotheses that are apposite for global scale comparisons, namely water-energy dynamics, biome stability, and ecological heterogeneity. Water-energy dynamics appear to have little influence in explaining these diversity patterns: nodes of high global plant diversity are associated with climates that support year-round plant production (tropical climates) and those where the growing season is constrained by a winter rainfall regime (Mediterranean-type climates). Moreover, while the Afrotropics have higher primary production than the Neotropics and Southeast Asian tropics, they have markedly lower plant diversity. Instead, these patterns appear to be consistent with the hypothesis that the synergy of historical biome stability (reducing extinction rates) and high ecological heterogeneity (promoting speciation rates) better explain global patterns of regional-scale plant diversity.

Plantations, and associated invasions, of exotic Pinus trees occur extensively in the southern hemisphere, threatening the persistence of biodiverse Mediterranean‐climate vegetation. Large‐scale decommissioning of such plantations in the eastern Cape Floristic Region (South Africa) enabled a wide‐ranging study showing successful passive restoration of fynbos vegetation after afforestation. Using a paired study design, we compared the diversity, and floristic and growth‐form composition of post‐fire recovering fynbos in former plantations with that in recently burnt neighboring fynbos in a natural state within the Garden Route National Park. The fynbos of the study area showed good autogenic recovery after several decades of pine afforestation and a fire subsequent to the clearcutting of these trees. On average, native plant abundance and species richness (particularly of shrubs) were significantly lower, and non‐native plant species richness significantly higher, in former plantation areas than in natural fynbos, but these differences were small. Species diversity (Shannon–Wiener index) did not differ significantly between the two vegetation states. The former plantations harbored 91% of the number of native species that the natural fynbos had, while the similarity of the two floras was 65%. Non‐metric multidimensional scaling ordination and multivariate generalized linear models accordingly showed no clear distinction in community composition between the two vegetation states. We concluded that the restoration potential of the montane grassy fynbos in the study area is superior to that previously documented in montane proteoid fynbos, and that fire and invasive alien plant control after clearcutting of the plantations is essential to promote fynbos restoration. [ABSTRACT FROM AUTHOR]

Fire plays a pivotal role in driving ecological shifts between Mediterranean‐type vegetation and subtropical ecosystems in South Africa. This study investigates long‐term environmental dynamics and ecological regime changes at the Mediterranean‐type vegetation /subtropical boundary using a 6000‐year palaeoecological sequence from the Baviaanskloof – a region of South Africa characterized by high levels of biodiversity and climate dynamism. Combining fossil pollen and microcharcoal data from a rock hyrax Procavia capensis midden, we analyse vegetation responses to environmental changes. Our findings reveal that Mediterranean‐type vegetation resilience prevailed until ca 2800 cal year BP when a major fire event triggered a transition to a subtropical thicket‐dominated environment. This abrupt ecological turnover underscores the significance of fire as a major driver of vegetation change at the Mediterranean‐type vegetation /subtropical boundary. Our study emphasizes the vulnerability of Mediterranean‐type vegetation ecosystems to global environmental change, suggesting potential implications for similar biome boundaries worldwide. By integrating multi‐proxy palaeoecological evidence, we gain insights into the resilience and vulnerability of these ecosystems, aiding in understanding future responses to climate change scenarios. [ABSTRACT FROM AUTHOR]