Pantropical variability in tree crown allometry

Aim Tree crowns determine light interception, carbon and water exchange. Thus, understanding the factors causing tree crown allometry to vary at the tree and stand level matters greatly for the development of future vegetation modelling and for the calibration of remote sensing products. Nevertheless, we know little about large‐scale variation and determinants in tropical tree crown allometry. In this study, we explored the continental variation in scaling exponents of site‐specific crown allometry and assessed their relationships with environmental and stand‐level variables in the tropics. Location Global tropics. Time period Early 21st century. Major taxa studied Woody plants. Methods Using a dataset of 87,737 trees distributed among 245 forest and savanna sites across the tropics, we fitted site‐specific allometric relationships between crown dimensions (crown depth, diameter and volume) and stem diameter using power‐law models. Stand‐level and environmental drivers of crown allometric relationships were assessed at pantropical and continental scales. Results The scaling exponents of allometric relationships between stem diameter and crown dimensions were higher in savannas than in forests. We identified that continental crown models were better than pantropical crown models and that continental differences in crown allometric relationships were driven by both stand‐level (wood density) and environmental (precipitation, cation exchange capacity and soil texture) variables for both tropical biomes. For a given diameter, forest trees from Asia and savanna trees from Australia had smaller crown dimensions than trees in Africa and America, with crown volumes for some Asian forest trees being smaller than those of trees in African forests. Main conclusions Our results provide new insight into geographical variability, with large continental differences in tropical tree crown allometry that were driven by stand‐level and environmental variables. They have implications for the assessment of ecosystem function and for the monitoring of woody biomass by remote sensing techniques in the global tropics

Disentangling the effects of topography and space on the distributions of dominant species in a subtropical forest

Topography and space are two important factors determining plant species assemblages in forest communities. Quantification of the contribution of these two factors in determining species distribution helps us to evaluate their relative importance in determining species assemblages. This study aims to disentangle the effect of topography and space on the distributions of 14 dominant species in a subtropical mixed forest. Spearman correlation analysis and the torus-translation test were used to test the species-habitat associations. Variation partitioning was used to quantify the relative contributions of topography and space at three sampling scales and three life stages. Correlation analyses and torus-translation tests showed species abundance was mostly correlated with topographic wetness index, vertical distance from the channel network and convexity. Variation partitioning showed that pure topography, pure space and spatially structured topography explained about 2.1 %, 41.2 % and 13.8 % of the variation in species distributions, respectively. For nine species, total topography fractions peaked in 20 m quadrats. For ten species, the pure space fractions peaked in 50 m quadrats. For many species, the total topography fraction and the pure space fraction were larger for the most abundant life stages, which reflected the importance of sampling effect. However, some cases did not follow this trend suggesting that the effects of ecological processes such as habitat filtering, density dependence or dispersal limitation may exceed the sampling effects. In conclusion, we found that spatially structured topography and pure space primarily shaped the distribution of dominant tree species. Furthermore, their effects were both scale-and life stage-dependent

Effects of topography on structuring species assemblages in a subtropical forest

Aims Topography has long been recognized as an important factor in shaping species distributions. Many studies revealed that species may show species-habitat associations. However, few studies investigate how species assemblages are associated with local habitats, and it still remains unclear how the community-habitat associations vary with species abundance class and life stage. In this study, we analyzed the community-habitat associations in a subtropical montane forest. Methods The fully mapped 25-ha (500 x 500 m) forest plot is located in Badagongshan Nature Reserve in Hunan Province, Central China. It was divided into 625 (20 x 20 m) quadrats. Habitat types were classified by multivariate regression tree analyses that cluster areas with similar species composition according to the topographic characteristics. Indicator species analysis was used to identify the most important species for structuring species assemblages. We also compared the community-habitat associations for two levels of species abundances (i.e. abundant and rare) and three different life stages (i.e. saplings, juveniles and adults), while accounting for sample size effects. Important Findings The Badagongshan plot was divided into five distinct habitat types, which explained 34.7% of the variance in tree species composition. Even with sample size taken into account, community-habitat associations for rare species were much weaker than those for abundant species. Also when accounting for sample size, very small differences were found in the variance explained by topography for the three life stages. Indicator species of habitat types were mainly abundant species, and nearly all adult stage indicator species were also indicators in juvenile and sapling stages. Our study manifested that topographical habitat filtering was important in shaping overall local species compositions. However, habitat filtering was not important in shaping rare species' distributions in this forest. The community-habitat association patterns in this forest were mainly shaped by abundant species. In addition, during the transitions from saplings to juveniles, and from juveniles to adults, the relative importance of habitat filtering was very weak

Disentangling the effects of topography and space on the distributions of dominant species in a subtropical forest

Topography and space are two important factors determining plant species assemblages in forest communities. Quantification of the contribution of these two factors in determining species distribution helps us to evaluate their relative importance in determining species assemblages. This study aims to disentangle the effect of topography and space on the distributions of 14 dominant species in a subtropical mixed forest. Spearman correlation analysis and the torus-translation test were used to test the species-habitat associations. Variation partitioning was used to quantify the relative contributions of topography and space at three sampling scales and three life stages. Correlation analyses and torus-translation tests showed species abundance was mostly correlated with topographic wetness index, vertical distance from the channel network and convexity. Variation partitioning showed that pure topography, pure space and spatially structured topography explained about 2.1 %, 41.2 % and 13.8 % of the variation in species distributions, respectively. For nine species, total topography fractions peaked in 20 m quadrats. For ten species, the pure space fractions peaked in 50 m quadrats. For many species, the total topography fraction and the pure space fraction were larger for the most abundant life stages, which reflected the importance of sampling effect. However, some cases did not follow this trend suggesting that the effects of ecological processes such as habitat filtering, density dependence or dispersal limitation may exceed the sampling effects. In conclusion, we found that spatially structured topography and pure space primarily shaped the distribution of dominant tree species. Furthermore, their effects were both scale-and life stage-dependent

Supplement 1. Data files used to develop allometry models in the main text.

<h2>File List</h2><div> <p><a href="data.csv">data.csv</a> (MD5: 7c7fdea693fcf4010735192c2588db9b)</p></div><h2>Description</h2><div> <p>The data.csv file is a csv file, it contains the raw data of diameter at breast height, tree height, wood specific gravity, crown radius, above-ground biomass and below-ground biomass.</p> <p>Column definitions</p> <blockquote> <p>1 DBH: diameter at breast height</p> <p>2 H: tree height</p> <p>3 WSG:wood specific gravity</p> <p>4 CR:crown radius</p> <p>5 AGB: above-ground biomass </p> <p>6 BGB: below-ground biomass </p> </blockquote> </div

Appendix A. A table showing equations for estimating aboveground biomass in subtropical forests, a figure showing Trace plot and density plot for each parameter in model I.1, and a figure showing within-chain variation for each parameter in model I.1.

A table showing equations for estimating aboveground biomass in subtropical forests, a figure showing Trace plot and density plot for each parameter in model I.1, and a figure showing within-chain variation for each parameter in model I.1

Foundation species across a latitudinal gradient in China

Foundation species structure forest communities and ecosystems but are difficult to identify without long-term observations or experiments. We used statistical criteria--outliers from size-frequency distributions and scale-dependent negative effects on alpha diversity and positive effects on beta diversity--to identify candidate foundation woody plant species in 12 large forest-dynamics plots spanning 26 degrees of latitude in China. We used these data (1) to identify candidate foundation species in Chinese forests, (2) to test the hypothesis--based on observations of a midlatitude peak in functional trait diversity and high local species richness but few numerically dominant species in tropical forests--that foundation woody plant species are more frequent in temperate than tropical or boreal forests, and (3) to compare these results with data from the Americas to suggest candidate foundation genera in northern hemisphere forests. Using the most stringent criteria, only two species of Acer, the canopy tree Acer ukurunduense and the shrubby treelet Acer barbinerve, were identified in temperate plots as candidate foundation species. Using more relaxed criteria, we identified four times more candidate foundation species in temperate plots (including species of Acer, Pinus, Juglans, Padus, Tilia, Fraxinus, Prunus, Taxus, Ulmus, and Corlyus) than in (sub)tropical plots (the treelets or shrubs Aporosa yunnanensis, Ficus hispida, Brassaiopsis glomerulata, and Orophea laui). Species diversity of co-occurring woody species was negatively associated with basal area of candidate foundation species more frequently at 5- and 10-m spatial grains (scale) than at a 20-m grain. Conversely, Bray-Curtis dissimilarity was positively associated with basal area of candidate foundation species more frequently at 5-m than at 10- or 20-m grains. Both stringent and relaxed criteria supported the hypothesis that foundation species are more common in mid-latitude temperate forests. Comparisons of candidate foundation species in Chinese and North American forests suggest that Acer be investigated further as a foundation tree genus

The proportion of species pairs significantly departed from Heterogeneous Poisson model and the proportion of no fine-scale species interactions cross life forms.

<p>Goodness-of-Fit tests were used to test the overall fit of the Heterogeneous Poisson model over 0−30 m distance interval with the 0.05 error rate under 199 simulations; Arbor-shrub indicates the fine-scale species interaction between arbor species and shrub species; Deciduous-Evergreen indicates the fine-scale species interactions between deciduous species and evergreen species.</p

Overall interspecific association patterns in dependence on the scale r.

<p>Overall interspecific association patterns in dependence on the scale r.</p