Abstract
Whether current hypotheses for geographic patterns of species richness (SR) have a strong explanatory power for the Tibetan Plateau (TP) with extreme climatic conditions remains unclear. In comparison with the classic ‘water–energy dynamics hypothesis', the unique climate factors (e.g. extreme low temperature and low oxygen partial pressure) on the TP likely significantly affect the spatial variation of SR. Here, we investigate geographic patterns and determinants of SR on the TP through a systematic field investigation. We systematically analyzed a total of 2013 plant communities covering 11 different vegetation types on the TP. To compare this SR with that of other sites across the globe, we compiled a global database containing information on 87 forest and 3660 grassland plots. The SR per 400 m2 in the forests and shrubs and that per 1 m2 in alpine grasslands and deserts was 62.76 (± 1.80 SE), 44.53 (± 7.57 SE), 16.84 (± 0.39 SE) and 3.62 (± 0.55 SE), respectively. The SR of forests and shrubs decreased with latitude and altitude, whereas that of alpine grasslands and deserts showed a unimodal pattern along the altitudinal gradient. Unique climate factors, such as extreme low temperature, mean diurnal temperature and oxygen partial pressure, act synergistically with water–energy dynamics and influence the spatial pattern of SR on the TP. Furthermore, the tree SR on the TP was lower than that of global tropical and subtropical broadleaf forests but higher than that of temperate conifer forests. Alpine meadows had a higher SR than other sites; however, the SR in alpine desert grasslands and alpine deserts was lower. Our findings provide novel insights into the mechanisms underlying the spatial variation in plant diversity, especially on plateaus and in high‐latitude regions. Our findings and the SR map with 1 km resolution provide important benchmarks for biodiversity conservation and may help to improve predictions of the effect of climate change on biodiversity.
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