Are allometric model parameters of aboveground biomass for trees phylogenetically constrained?

Evolutionary history shapes variation of wood density of tree species across the world

The effect of evolutionary history on wood density variation may play an important role in shaping variation in wood density, but this has largely not been tested. Using a comprehensive global dataset including 27,297 measurements of wood density from 2621 tree species worldwide, we test the hypothesis that the legacy of evolutionary history plays an important role in driving the variation of wood density among tree species. We assessed phylogenetic signal in different taxonomic (e.g., angiosperms and gymnosperms) and ecological (e.g., tropical, temperate, and boreal) groups of tree species, explored the biogeographical and phylogenetic patterns of wood density, and quantified the relative importance of current environmental factors (e.g., climatic and soil variables) and evolutionary history (i.e., phylogenetic relatedness among species and lineages) in driving global wood density variation. We found that wood density displayed a significant phylogenetic signal. Wood density differed among different biomes and climatic zones, with higher mean values of wood density in relatively drier regions (highest in subtropical desert). Our study revealed that at a global scale, for angiosperms and gymnosperms combined, phylogeny and species (representing the variance explained by taxonomy and not direct explained by long-term evolution process) explained 84.3% and 7.7% of total wood density variation, respectively, whereas current environment explained 2.7% of total wood density variation when phylogeny and species were taken into account. When angiosperms and gymnosperms were considered separately, the three proportions of explained variation are, respectively, 84.2%, 7.5% and 6.7% for angiosperms, and 45.7%, 21.3% and 18.6% for gymnosperms. Our study shows that evolutionary history outpaced current environmental factors in shaping global variation in wood density.

Drivers of the differentiation between broad-leaved trees and shrubs in the shift from evergreen to deciduous leaf habit in forests of eastern Asian subtropics

In eastern Asian subtropical forests, leaf habit shifts from evergreen to deciduous broad-leaved woody plants toward higher latitudes. This shift has been largely explained by the greater capacity of deciduous broad-leaved plants to respond to harsh climatic conditions (e.g., greater seasonality). The advantages of deciduous leaf habit over evergreen leaf habit in more seasonal climates have led us to hypothesize that leaf habits would shift in response to climate changes more conspicuously in forest canopy trees than in forest understory shrubs. Furthermore, we hypothesize that in the forests of the subtropics, plants at higher latitudes, regardless of growth form, would better tolerate seasonal harsh climates, and hence show less differentiation in leaf habit shift, compared to those at lower latitudes. To test these two hypotheses, we modelled the proportion of deciduous broad-leaved species and the incidence of deciduous and evergreen broad-leaved species in woody angiosperm species compositions of ten large-sized forest plots distributed in the Chinese subtropics. We found that the rate of leaf habit shift along a latitudinal gradient was higher in forest trees than in forest shrubs. We also found that the differentiation in leaf habit shift between trees and shrubs is greater at lower latitudes (i.e., warmer climates) than at higher latitudes (i.e., colder climates). These findings indicate that specialized forest plants are differentially affected by climate in distinct forest strata in a manner dependent on latitudinal distribution. These differences in forest plant response to changes in climate suggest that global climate warming will alter growth forms and geographical distributions and ranges of forests.

Geographic patterns of taxonomic and phylogenetic β-diversity of angiosperm genera in regional floras across the world

Beta diversity (β-diversity) is the scalar between local (α) and regional (γ) diversity. Understanding geographic patterns of β-diversity is central to ecology, biogeography, and conservation biology. A full understanding of the origin and maintenance of geographic patterns of β-diversity requires exploring both taxonomic and phylogenetic β-diversity, as well as their respective turnover and nestedness components, and exploring phylogenetic β-diversity at different evolutionary depths. In this study, we explore and map geographic patterns of β-diversity for angiosperm genera in regional floras across the world. We examine both taxonomic and phylogenetic β-diversity and their constituent components, and both tip-weighted and basal-weighted phylogenetic β-diversity, and relate them to latitude. On the one hand, our study found that the global distribution of β-diversity is highly heterogeneous. This is the case for both taxonomic and phylogenetic β-diversity, and for both tip-weighted and basal-weighted phylogenetic β-diversity. On the other hand, our study found that there are highly consistent geographic patterns among different metrics of β-diversity. In most cases, metrics of β-diversity are negatively associated with latitude, particularly in the Northern Hemisphere. Different metrics of taxonomic β-diversity are strongly and positively correlated with their counterparts of phylogenetic β-diversity.

Geographic patterns of taxonomic and phylogenetic β-diversity of aquatic angiosperms in China

China covers a vast territory harbouring a large number of aquatic plants. Although there are many studies on the β-diversity of total, herbaceous or woody plants in China and elsewhere, few studies have focused on aquatic plants. Here, we analyse a comprehensive data set of 889 aquatic angiosperm species in China, and explore the geographic patterns and climatic correlates of total taxonomic and phylogenetic β-diversity as well as their turnover and nestedness components. Our results show that geographic patterns of taxonomic and phylogenetic β-diversity are highly congruent for aquatic angiosperms, and taxonomic β-diversity is consistently higher than phylogenetic β-diversity. The ratio between the nestedness component and total β-diversity is high in northwestern China and low in southeastern China. The geographic patterns of taxonomic and phylogenetic β-diversity of aquatic angiosperms in China are obviously affected by geographic and climatic distances, respectively. In conclusion, the geographic patterns of taxonomic and phylogenetic β-diversity of aquatic angiosperms are consistent across China. Climatic and geographic distances jointly affect the geographic patterns of β-diversity of aquatic angiosperms. Overall, our work provides insight into understanding the large-scale patterns of aquatic angiosperm β-diversity, and is a critical addition to previous studies on the macroecological patterns of terrestrial organisms.