Why are plant species in hot, dry scrublands often less diverse than those in Mediterranean scrublands?

Plant species in hot, dry scrublands are generally less diverse than those in Mediterranean scrublands primarily due to the severity of their environmental conditions. While Mediterranean scrublands are characterized by a predictable climate of mild, moist winters and hot, dry summers, scrublands in hotter, drier regions face more extreme and erratic moisture shortages.1

In these hotter, drier environments, rainfall is not only low but also highly unpredictable, and its effectiveness is further diminished by extremely high rates of potential evapotranspiration. These harsh conditions create a more challenging environment for plant life compared to the Mediterranean climate, where vegetation has evolved specific adaptations to survive seasonal drought and fire regimes.12

Furthermore, while Mediterranean scrublands—such as the fynbos of South Africa or those in Western Australia—can exhibit astonishingly high plant diversity, this is often linked to specific factors like nutrient-poor soils that have persisted over long periods. In contrast, the more extreme aridity and heat of other scrubland regions limit the number of species that can successfully establish and thrive, resulting in lower overall floristic richness.13