Functional traits of tree species with phylogenetic signal co-vary with environmental niches in two large forest dynamics plots

Aims While using phylogenetic and functional approaches to test the mechanisms of community assembly,functional traits often act as the proxy of niches.However,there is little detailed knowledge regarding the correlation between functional traits of tree species and their niches in local communities.We suggest that the co-varying correlation between functional traits and niches should be the premise for using phylogenetic and functional approaches to test mechanisms of community assembly.Using functional traits,phylogenetic and environmental data,this study aims to answer the questions:(i)within local communities,do functional traits of co-occurring species covary with their environmental niches at the species level?and(ii)what is the key ecological process underlying community assembly in Xishuangbanna and Ailaoshan forest dynamic plots(FDPs)?Methods We measured seven functional traits of 229 and 36 common species in Xishuangbanna and Ailaoshan FDPs in tropical and subtropical China,respectively.We also quantified the environmental niches for these species based on conditional probability.We then analyzed the correlations between functional traits and environmental niches using phylogenetic independent contrasts.After examining phylogenetic signals of functional traits using Pagel’sλ,we quantified the phylogenetic and functional dispersion along environmental gradients within local tree communities.Important Findings For target species,functional traits do co-vary with environmental niches at the species level in both of the FDPs,supporting that functional traits can be used as a proxy for local-scale environmental niches.Functional traits show significant phylogenetic signals in both of the FDPs.We found that the phylogenetic and functional dispersion were significantly clustered along topographical gradients in the Ailaoshan FDP but overdispersion in the Xishuangbanna FDP.These patterns of phylogenetic and functional dispersion suggest that environmental filtering plays a key role in structuring local tree assemblages in Ailaoshan FDP,while competition exclusion plays a key role in Xishuangbanna FDP.

Altitudinal patterns of maximum plant height on the Tibetan Plateau

Aims Several studies have shown that plant height changes along environmen-tal gradients.However,altitudinal patterns of plant height across species are still unclear,especially in regions sensitive to climate change.As canopy height decreases dramatically near the tree line in alpine areas,we hypothesize that plant height across all species also decreases with increasing altitude,and distinct thresholds exist along this gradient.Methods Using a large dataset of maximum plant height and elevation range(400 to 6000 m a.s.l.)of 4295 angiosperms from the regional flora of the Tibetan Plateau,we regressed plant height for every 100 m belt against elevation to explore the relationships.To identify the approximate boundaries where dramatic changes in plant height occurs for herbaceous plants,shrubs,trees,woody plants and all angiosperms,we used piecewise linear regression.Phylogenetically independent contrast was used to test the potential evolutionary influences on altitudinal patterns at the family level.Important Findings Results showed that for herbaceous plants,shrubs,trees,woody plants and all angiosperms,plant height decreases significantly as altitude increases.In addition,we found that altitude,a proxy for many environmental factors,had obvious thresholds(breakpoints)dictating patterns of plant height.The results of phylogenetically independent contrast also emphasized the importance of evolution-ary history in determining the altitudinal patterns of plant height for some growth forms.Our results highlight the relative intense filter-ing effect of environmental factors in shaping patterns of functional traits and how this could vary for different ranges of environmental variables.