Direct and indirect effects of climate on richness drive the latitudinal diversity gradient in forest trees

Data accessibility statement: Full census data are available upon reasonable request from the ForestGEO data portal, http://ctfs.si.edu/datarequest/ We thank Margie Mayfield, three anonymous reviewers and Jacob Weiner for constructive comments on the manuscript. This study was financially supported by the National Key R&D Program of China (2017YFC0506100), the National Natural Science Foundation of China (31622014 and 31570426), and the Fundamental Research Funds for the Central Universities (17lgzd24) to CC. XW was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB3103). DS was supported by the Czech Science Foundation (grant no. 16-26369S). Yves Rosseel provided us valuable suggestions on using the lavaan package conducting SEM analyses. Funding and citation information for each forest plot is available in the Supplementary Information Text 1.Peer reviewedPostprin

Interactions between all pairs of neighboring trees in 16 forests worldwide reveal details of unique ecological processes in each forest, and provide windows into their evolutionary histories

When Darwin visited the Galapagos archipelago, he observed that, in spite of the islands’ physical similarity, members of species that had dispersed to them recently were beginning to diverge from each other. He postulated that these divergences must have resulted primarily from interactions with sets of other species that had also diverged across these otherwise similar islands. By extrapolation, if Darwin is correct, such complex interactions must be driving species divergences across all ecosystems. However, many current general ecological theories that predict observed distributions of species in ecosystems do not take the details of between-species interactions into account. Here we quantify, in sixteen forest diversity plots (FDPs) worldwide, highly significant negative density-dependent (NDD) components of both conspecific and heterospecific between-tree interactions that affect the trees’ distributions, growth, recruitment, and mortality. These interactions decline smoothly in significance with increasing physical distance between trees. They also tend to decline in significance with increasing phylogenetic distance between the trees, but each FDP exhibits its own unique pattern of exceptions to this overall decline. Unique patterns of between-species interactions in ecosystems, of the general type that Darwin postulated, are likely to have contributed to the exceptions. We test the power of our null-model method by using a deliberately modified data set, and show that the method easily identifies the modifications. We examine how some of the exceptions, at the Wind River (USA) FDP, reveal new details of a known allelopathic effect of one of the Wind River gymnosperm species. Finally, we explore how similar analyses can be used to investigate details of many types of interactions in these complex ecosystems, and can provide clues to the evolution of these interactions

Root-centric β diversity reveals functional homogeneity while phylogenetic heterogeneity in a subtropical forest

<p>Root-centric studies have revealed fast taxonomic turnover across root neighborhoods, but how such turnover is accompanied by changes in species functions and phylogeny (i.e. β diversity), which can reflect the degree of community-wide biotic homogenization, remains largely unknown, hindering better inference of below-ground assembly rules, community structuring, and ecosystem processes. We collected 2480 root segments from 625 0–30 cm soil profiles in a subtropical forest in China. Root segments were identified into 143 species with DNA-barcoding with six root morphological and architectural traits measured per species. By using the mean pairwise (Dpw) and mean nearest neighbor distance (Dnn) to quantify species ecological differences, we tested the non-random functional and phylogenetic turnover of root neighborhoods that would lend more support to deterministic over stochastic community assembly processes, examined the distance-decay pattern of β diversity, and finally partitioned β diversity into geographical and environmental components to infer their potential drivers of environmental filtering, dispersal limitation, and biotic interactions. We found that functional turnover was often lower than expected given the taxonomic turnover, whereas phylogenetic turnover was often higher than expected. Both functional and phylogenetic Dpw (e.g. interfamily species) turnover exhibited a distance-decay pattern, likely reflecting limited dispersal or abiotic filtering that leads to the spatial aggregation of specific plant lineages. Conversely, phylogenetic Dnn (e.g. intrageneric species) exhibited an inverted distance-decay pattern, likely reflecting strong biotic interactions among spatially and phylogenetically close species leading to phylogenetic divergence. While the spatial distance was generally a better predictor of β diversity than environmental distance, the joint effect of environmental and spatial distance usually overrode their respective pure effects. These findings suggest that root neighborhood functional homogeneity may somewhat increase forest resilience after disturbance by exhibiting an insurance effect. Likewise, root neighborhood phylogenetic heterogeneity may enhance plant fitness by hindering the transmission of host-specific pathogens through root networks or by promoting interspecific niche complementarity not captured by species functions. Our study highlights the potential role of root-centric β diversity in mediating community structures and functions largely ignored in previous studies.</p><p>These datasets were collected in the Guangdong Heishiding Dynamic Forest Plot in Southern China (2016). Details for each dataset are provided in the README file.</p><p>Funding provided by: National Natural Science Foundation of China<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100001809<br>Award Number: 31925027</p><p>Funding provided by: China Postdoctoral Science Foundation<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100002858<br>Award Number: 2021M70375</p><p>Funding provided by: Basic and Applied Basic Research Foundation of Guangdong Province<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100021171<br>Award Number: 2021A1515110362</p><p>Funding provided by: National Natural Science Foundation of China<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100001809<br>Award Number: 32301341</p&gt

Inconsistent elevational patterns of soil microbial biomass, diversity, and community structure on four elevational transects from subtropical forests

International audienc

How does functional distinctiveness affect single species contribution to β diversity? Evidence from a subtropical forest plot in southern China

To biologically interpret β diversity patterns, in terms of species characteristics, needs to quantify how each individual species contributes to overall β diversity (SCBD). However, the lack of studies linking SCBD to functional traits hinders to explore the full potential of the approach in biodiversity conservation. Here, we combined census data, species functional traits, and environmental variables from a 50-ha stem-mapped forest plot in southern China, with the aim to disentangle the relationship among SCBD, species functional traits and niche properties. We used nine functional traits to estimate species functional distinctiveness, and eleven environmental variables were used to compute species niche properties (niche position and niche breadth). Structural equation modeling (SEM) was applied to analyze how functional distinctiveness and niche properties jointly influenced SCBD. Results found that species with more unique trait combinations (higher functional distinctiveness) occupied marginal niche position and maintained smaller niche breadths and thus contributed less to overall β diversity. Meanwhile, functional distinctiveness and niche properties jointly determined SCBD. In addition, we found a negative effect of functional distinctiveness on SCBD, which implies the urgency of developing better biodiversity conservation strategies by unravelling the linkage between SCBD and ecosystem multifunctionality. These findings contribute to a better understanding of how species characteristics affect β diversity and making SCBD more applicable in biodiversity conservation

Habitat Conditions and Tree Species Shape Liana Distribution in a Subtropical Forest

Lianas are woody plants that require external support to reach the canopy. They are expanding in forests worldwide, possibly due to climate change and forest disturbance. Most studies on lianas have been conducted in tropical forests. Lianas are less explored in subtropical forests. We aimed to document the density and diversity of lianas, to test how habitat condition and the distribution of tree species affect the distributions of lianas based on data from a fully mapped 20 ha plot in subtropical China. We analyzed habitat association by fitting a generalized linear model with family-level liana abundance as response variable and family identity, and its interaction terms with topographic variables (slope, convexity, elevation, and sin(aspect)), as explanatory variables. We focused on the spatial associations of three liana species and 82 tree species with ≥100 individuals using the pair correlation function and redundancy analysis. We found a total of 1305 lianas, falling into 26 species, and 16 families, in the 20 ha plot. They accounted for 1.5% of individuals, 11.7% of species, and 0.4% of total basal area of woody plants in the plot. There were large variations in distributions of liana with respect to the four topographic variables among families, contrasting with former findings suggesting that lianas favor dry and hot habitats. The three most abundant liana species showed non-random associations with tree species, and they tended to positively associate with similar tree species but negatively associate with different tree species. The distribution of tree species explained 21.8% of variance in liana distribution. Our study suggested that both habitat conditions and tree composition intervene in determining liana distributions and that habitat heterogeneity may be a mechanism for liana diversity maintenance. Our study provides a basic understanding of liana diversity and distribution in this subtropical forest and contributes to future planning of liana studies and diversity conservation in subtropical forests under climate change

Nonsignificant elevational trends of soil microbial respiration and temperature sensitivity in a subtropical forest

International audienceAbstract Soil carbon (C) cycling plays a critical role in regulating global C budget and atmospheric CO 2 concentrations. The ongoing global warming potentially accelerates soil C loss induced by microbial respiration (MR) and makes soil a large C source to the atmosphere. Quantifying the drivers of MR and its response to rising temperature (also called temperature sensitivity, Q 10 ) should be a high priority to improve the modeling and prediction of terrestrial C cycle under global warming. In this study, we applied a standardized soil sampling along nine gradients from 410 to 1080 m in a subtropical forest in southern China. All soil samples were incubated at varying temperature gradients (10–15–20–25–20–15°C) to measure MR and Q 10 every day for three weeks. Then all the measured MR was adjusted by the field temperature of each elevation gradient. Our objectives were to examine the response of MR and Q 10 to the environmental change induced by elevational gradients in the subtropical forest and then quantify their main drivers. We totally collected 54 abiotic and biotic factors relative to the MR and Q 10 . Our results showed that the incubated MR increased from low to high elevation. However, a significant elevation trend of the adjusted MR was not examined after adjusting the field temperature of sampling sites, due to the trade‐off between increasing soil C concentration and declining temperature as elevation increased. We further found that the elevational gradients did not cause significant change in Q 10 . The variation in Q 10 was negatively dominated by soil C quality, which declined nonlinearly along the elevation gradients. This study highlights the trade‐off between environment and biotic factors in determining soil C decomposition along elevational gradients. The uncertainty of MR measurements caused by unifying incubated temperature should not be ignored in future model development

Does local soil factor drive functional leaf trait variation? A test on Neilingding Island, South China

Abstract Leaf traits were affected by soil factors and displayed varietal differences in forest. However, few examples have been reported on the Island ecosystems. We comprehensively investigated 9 leaf traits (leaf length, leaf width, leaf area, SLA, leaf fresh weight, leaf C content, leaf N content, leaf K content, leaf C:N ratio) of 54 main subtropical woody species and soil parameters (soil pH, total C content, total N content, total K content, available N content, available P content, available K content and soil moisture) in Neilingding Island, Shenzhen, southern China. Intra-and interspecific variation of leaf traits were measured and their correlations with soil parameters were explored. The interspecific variations of leaf C:N ratio, leaf N content and leaf fresh weight were higher than their intraspecific variations. The intraspecific variation of leaf K content was larger than that of interspecific one, accounting for 80.69% of the total variance. Positive correlations were found among intraspecific coefficients of variations in leaf morphological traits. The correlation analysis between the variation of intraspecific traits and the variation of soil parameters showed that changes in soil factors affected leaf morphology and stoichiometry. The interaction between soil moisture and soil available P content was the key factor on intraspecific variations of leaf traits including leaf area, leaf fresh weight, leaf C and leaf K content. We concluded that leaf traits of plants in the island were tightly related to soil parameters. Soil parameters, especially soil moisture and available P content, affected plant leaf morphology and stoichiometry at the local scale

Density dependence on tree survival in an old-growth temperate forest in northeastern China

• Density dependence is a major mechanism for shaping plant communities. However, its role in regulating diverse, mixed natural tree communities is less certain. • In this study we investigated density-dependent effects in a large-scale (25 ha) old-growth temperate forest in northeastern China. Spatial patterns of neighborhood distribution in the plot were analyzed using various methods for inferring competition, including (1) pair correlation function to determine spatial patterns of pre-mortality and post-mortality and (2) neighborhood analysis of individuals to examine the extent to which tree survival is correlated with other covariates. • Results showed that, for common species, 3 of 5 canopy species and 3 of 8 midstory and understory species were random in mortality. Negative density-dependent mortality was not found when trees reach 1 cm in DBH. There was no significant correlation for canopy species between tree survival and conspecific abundance, but largely positive correlations for midstory and understory species. In contrast, tree survival was found to negatively correlate with conspecific basal area for most species, indicating strong intraspecific competition. No strong interspecific density dependence was found in the forest.La survie des arbres dépend de la densité dans une ancienne forêt tempérée du nord-est de la Chine. • La dépendance par rapport à la densité est un important mécanisme pour la formation des communautés végétales. Toutefois, son rôle dans la régulation de diverses communautés mélangées d'arbre est moins certain. • Dans cette étude, nous avons enquêté sur les effets densité-dépendance à une grande échelle (25 ha) dans une ancienne forêt tempérée, dans le nord de la Chine. Les modes de distribution spatiale de voisinage ont été analysés en utilisant diverses méthodes pour estimer la concurrence, y compris: (1) des paires de fonction de corrélation afin de déterminer les structures spatiales de pré et post-mortalité et (2) l'analyse du voisinage des individus pour examiner dans quelle mesure la survie de l'arbre survivant est corrélée avec d'autres variables. • Les résultats ont montré que, pour les espèces communes, 3 des 5 espèces de la canopée et 3 des 8 de l'étage moyen et du sous-étage, la mortalité était aléatoire. Aucune mortalité densité-dépendante négative n'a été détectée lorsque les arbres atteignent 1 cm de diamètre à hauteur d'homme. Il n'y avait pas de corrélation significative pour les espèces de la canopée entre la survie des arbres et l'abondance conspécifique, mais il y avait des corrélations positives pour l'étage moyen et le sous-étage. • En revanche, la survie des arbres était corrélée négativement avec la surface terrière conspécifique pour la plupart des espèces, indiquant une forte concurrence intraspécifique. Aucune dépendance visible de la densité interspécifique n'a été détectée dans la forêt