Spatio-temporal maintenance of flora in the Himalaya biodiversity hotspot: Current knowledge and future perspectives

Mountain ecosystems support a significant one-third of all terrestrial biodiversity, but our understanding of the spatio-temporal maintenance of this high biodiversity remains poor, or at best controversial. The Himalaya hosts a complex mountain ecosystem with high topographic and climatic heterogeneity, and harbor one of the world’s richest floras. The high species endemism, together with increasing anthropogenic threats, have qualified the Himalaya as one of the global biodiversity hotspots. The topographic and climatic complexity of the Himalaya make it an ideal natural laboratory for studying the mechanisms of floral exchange, diversification and spatio-temporal distributions. Here, we review literature pertaining to the Himalaya, to generate a concise synthesis of the origin, distribution and climate change responses of Himalayan flora. We found that the Himalaya supports a rich biodiversity, and that the Hengduan Mountains supplied the majority of the Himalayan floral elements, which subsequently diversified from the late Miocene onwards, to create today's relatively high endemicity in the Himalaya. Further, we uncover links between this Miocene diversification and the joint effect of geological and climatic upheavals in the Himalaya. There is marked variance regarding species dispersal, elevational gradients and impact of climate change among plant species in the Himalaya, and our review highlights some of the general trends and recent advances on these aspects. Finally, we provide some recommendations for conservation planning and future research. Our work could be useful in guiding future research in this important ecosystem, and will also provide new insights into the maintenance mechanisms underpinning other mountain systems.