Climate is widely recognised as an important determinant of the latitudinal diversity gradient. However, most existing studies make no distinction between direct and indirect effects of climate, which substantially hinders our understanding of how climate constrains biodiversity globally. Using data from 35 large forest plots, we test hypothesised relationships amongst climate, topography, forest structural attributes (stem abundance, tree size variation and stand basal area) and tree species richness to better understand drivers of latitudinal tree diversity patterns. Climate influences tree richness both directly, with more species in warm, moist, aseasonal climates and indirectly, with more species at higher stem abundance. These results imply direct limitation of species diversity by climatic stress and more rapid (co-)evolution and narrower niche partitioning in warm climates. They also support the idea that increased numbers of individuals associated with high primary productivity are partitioned to support a greater number of species. LetterClimate and the latitudinal tree diversity gradient 247 Figure 4 The effects of forest structural attributes on tree diversity derived from the within-forest plot structural equation modelling analyses. Panels a, b and c at the scale of 20 m 9 20 m, and panels d, e and f at the scale of 50 m 9 50 m. The effect of stem abundance on tree species richness showed a significant latitudinal trend at the scale of 20 m 9 20 m (panel b; P < 0.01, R 2 = 0.27). Standardised path coefficients AE 1 SE are shown; SE's are smaller than the size of the symbol for some forest plots. Colours indicate increasing absolute latitude from pink to turquoise.

Aim The Tibetan Plateau harbours the highest alpine and endemic plant diversity in the world, attributed to rapid diversification during the plateau uplift and Quaternary climate fluctuations. However, there is little understanding of which hypotheses associated with these geological and climatic processes garner strong support as explanations for the observed diversity patterns. Here, we test support for hypotheses related to uplift and climate changes that could account for the high endemicity and phylogenetic diversity of the world’s highest plateau. Location Tibetan Plateau (TP). Time period Neogene, Quaternary and current period. Major taxa studied Tibetan endemic seed plants. Methods We collated data on endemic seed‐plant distribution based on county‐level mapping from published monographs and online databases. We calculated species richness (SR) and phylogenetic diversity for endemic herbs, shrubs, trees, and all plants for 0.5‐degree × 0.5‐degree grid cells covering the TP. We derived environmental and evolutionary predictors to evaluate eight biogeographical hypotheses associated with plateau uplift and climate fluctuations, and used partial regression analysis and mixed conditional autoregressive (CAR) models to assess the relative contribution of each predictor to the extant diversity of the TP. Results We found plateau uplift independently explained more variance in diversity than climate fluctuations, but there were also strong interaction effects. The full CAR models including all predictors explained 37%–75% of the total variation across diversity measures and life forms. The predictor representing the montane museum hypothesis explained the most variation (c. 25%), but each predictor explained at least 6%. Main conclusions These results demonstrate that both the plateau uplift and Quaternary climate fluctuations had large impacts on current patterns of species diversity, but the influence of plateau uplift was more pronounced than that of climate changes. Our study suggests that plateau uplift and climate changes are the original drivers of complex biogeographical processes accounting for the biodiversity of the TP.

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Aim: Species diversity in the region of the Qinghai-Tibet Plateau has been extensively explored, whereas the distribution of genetic diversity remains poorly understood in this species-rich area, parts of which are listed as biodiversity hotspots. In this study, we aimed to map the patterns of genetic diversity and divergence of plant species in this region, and to identify potential evolutionary hotspots for conservation planning.Location: Region of the Qinghai-Tibet Plateau (QTP). Methods:We compiled published molecular data for 60 plant species, and calculated intra-population genetic diversity and inter-population genetic divergence using haplotype sequences (chloroplast or mitochondrial DNA). We analysed the relationships between genetic diversity and longitude, latitude and elevation. We mapped the landscapes of genetic diversity and divergence for each species in GIS, and combined the resulting landscapes in order to identify hotspots of high genetic diversity and divergence.Results: There were no significant relationships between genetic diversity and longitude, latitude and elevation. For most species, areas characterized by high genetic diversity and divergence were located across the Hengduan Mountains. Nine evolutionary hotspots across the region of the QTP were identified. Main conclusions:The Hengduan Mountains are a remarkable hotspot of all three dimensions of biodiversity (genes, species and ecosystems), yet patterns of genetic diversity were partially incongruent with the distribution of species diversity. For example, several hotspots of genetic diversity were located on the QTP proper, which is relatively species poor. This partial geographic mismatch between species and genetic diversity highlights the need to consider both aspects in conservation programs. Our study suggests that more protected areas in the region of the QTP need to be established in order to protect genetic diversity and thus adaptive potential. K E Y W O R D Sbiodiversity conservation, comparative phylogeography, evolutionary hotspots, genetic divergence, genetic diversity, Qinghai-Tibet Plateau, Quaternary refugia | 311 YU et al. Pedicularis kansuensisA,