Abstract
The Qinghai-Tibet Plateau sensu lato (QTP s.l.) harbors an exceptionally high biodiversity, especially at its southeastern margin: this area encompasses the Hengduan Mountains and the eastern Himalayas, which have been listed as biodiversity hotspots. To the contrary, the plateau interior (namely the Qinghai-Tibet Plateau sensu stricto, QTP s.s.) is relatively species-poor because of its particularly harsh climate. With contrasting geological histories and environmental conditions of the Hengduan Mountains, the Himalayas and the QTP s.s., it would be expected that floristic compositions and diversity patterns of these three regions would differ between each other. To compare the floristic diversity of these three regions, we assembled data on seed plant’s distribution in the three regions based on county-level mapping from published monographs and online databases, and we then analyzed their floristic features and species diversity patterns (horizontal and elevational). We found that the Hengduan Mountains hosted the most seed plant species (8,439), as expected. The highest percentage of shrub (22.88%) and tree species (9.80%) were in the Himalayas, whereas herbaceous species (81.50%) were relatively more prominent in the QTP s.s.. The Hengduan Mountains also had the most species-rich genera (10) with more than 50% of their total species diversity in China. Also, temperate genera dominated across these three regions, with a highest percentage (77.61%) within the QTP s.s.. Across the QTP s.l., species diversity gradually decreased from the southeastern part to the northwest, and most of seed plants were distributed in the southern and eastern margin of the Hengduan Mountains and East Himalayas. Along elevational gradients, species richness all demonstrated a hump-shape curve, but the most species-rich elevation zone differed for each type of life-form across the three regions. Our study sets a base for exploring the origin and evolution of mountain taxa, as well as provides a snapshot of the current plant distribution, which will certainly be modified by climate change.
Highlights
Mountainous regions harbor about one-quarter of terrestrial species, and inevitably, some of these areas have been listed as hotspots of biodiversity, including for example the two most diverse mountainous regions on Earth: the Andes and the Hengduan Mountains (Marchese, 2015; Hoorn et al, 2018)
The third and largest area (c. 1.8 × 106 km2) is the QTP s.s. itself, with a higher mean elevation (> c. 4,500 m) and harsh cold and dry climate in its northwestern part, whereas its eastern and southeastern margins have relatively warm and wet climate influenced by the East Asian monsoon
The QTP s.s. had the largest proportion of herbaceous species (3,185; 81.50%), with additional 556 (14.23%) shrubs and 167 (4.27%) tree species
Summary
Mountainous regions harbor about one-quarter of terrestrial species, and inevitably, some of these areas have been listed as hotspots of biodiversity, including for example the two most diverse mountainous regions on Earth: the Andes and the Hengduan Mountains (Marchese, 2015; Hoorn et al, 2018). The establishment of high biodiversity levels in these remarkable mountain systems is likely to result from the combination of global and local abiotic conditions (e.g., geological and climatic processes) with biotic, often taxon-specific features (e.g., key innovations) (Lagomarsino et al, 2016). Mountain building and past climate changes are crucial triggers of complex evolutionary processes accounting for species diversity in mountains (Antonelli et al, 2018; Rahbek et al, 2019). Understanding the profile of species diversity in such a region could provide general and valuable insights into the recent evolution of local taxa, as well as help prioritizing conservation strategies of regional biota
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