Functional traits are widely used to predict species redistribution under climate change because traits determine how plants interact with the environment and shape population dynamics, which ultimately drive range shifts. However, traits still have limited ability to predict range shifts, as the pathways linking traits to demographic processes and subsequently to range shifts are poorly understood. Using 15 years of forest census data for 74 tree species and key functional traits representing distinct ecological strategies (e.g., specific leaf area and wood density), we found that tree elevational range shifts were driven primarily by recruitment rather than mortality. Functional traits influenced range shifts through specific pathways: species with higher structural investment (e.g., high wood density) exhibited higher recruitment rates at upper elevations and shifted upward, whereas resource acquisition traits (e.g., specific leaf area) directly accelerated the upward shift of range centers. Our findings demonstrated the complex pathways that traits mediate tree range shifts and highlight recruitment as the crucial process for improving trait-based predictions of tree range shifts. Ultimately, our framework provides forest managers with an actionable, trait-based tool to guide species selection, assisted migration, and proactive conservation in warming climates.

Climate change is exacerbating tree mortality worldwide, threatening the stability of forest soil organic carbon (SOC) stocks. However, how SOC responds to tree mortality amid co-occurring disturbances remains mechanistically unresolved. Here, we demonstrate that topography spatially decouples the canopy-opening and detrital-legacy effects of tree mortality and transforms these co-occurring disturbances into distinct selective pressures on soil microbial communities, thereby driving SOC toward contrasting fates through divergent microbial strategies for carbon and energy acquisition. On ridges, canopy-opening effects co-select for exo-enzyme and aerobic-respiration traits, alongside SOC loss associated with reduced heavy-fraction organic carbon. In valleys, detrital-legacy effects promote light-fraction-associated SOC gain while co-enriching endo-enzyme and anaerobic-respiration traits, potentially strengthening SOC retention. By integrating amplicon sequencing with genome-informed functional traits, our study provides genomic evidence for the microbial mechanisms underlying divergent SOC responses to tree mortality and highlights the potential of genome-based microbial traits for predicting ecosystem-scale biogeochemical processes. Topography spatially decouples the canopy-opening and detrital-legacy effects of tree mortality, creating distinct pressures on soil microbes that drive soil carbon toward contrasting fates through divergent microbial strategies.

Abstract Population stability (PS) of functionally important species underpins ecosystem resilience, yet the mechanisms that maintain PS under heterogeneous nitrogen (N) conditions remain elusive, particularly for legumes in (sub)tropical forests. Legumes can stabilize their population performance through high abundance or symbiotic N2 fixation, but how soil N “chooses” between these strategies is unknown. In a 20-ha subtropical forest plot, the sole dominant legume Ormosia glaberrima, with >2,500 individuals recorded over 15 years, provides an ideal system to test these pathways. We quantified PS from long-term demography as the inverse of inter-period variation in basal area growth, and assessed biological N fixation (BNF) ability using the N stable isotope natural abundance method. Structural equation modeling (SEM) was applied to disentangle the direct and indirect effects of soil N, abundance, and BNF ability on PS. Results showed no significant direct effect of soil N on the PS of O. glaberrima. Instead, it was positively correlated with abundance (R2adj =0.22, P < 0.001) and negatively related to BNF ability (R2adj =0.26, P < 0.001). SEM explained 34% of the variation in PS and revealed opposing mediating pathways. Elevated soil N indirectly enhanced PS by increasing abundance (β = 0.27) but reduced PS by suppressing BNF ability (β = -0.15). These findings reveal a context-dependent “abundance-fixation trade-off” as a novel mechanism regulating long-term legume population performance, with important implications for forest management aimed at maintaining ecosystem stability under global N deposition.

Abstract The functional basis of tree growth is often evaluated based on trunk diameter even though diameter is only one dimension of growth that may not be an integrative measure of resource allocation. We tested the hypothesis that growth—functional trait relationships are stronger when key sources of variation in tree growth are also accounted for, namely tree height and DBH, as well as size‐related variation in wood density and seed production using data from 3881 trees of 24 species in a subtropical forest using ordinary least square regression and standard major axis regression. Wood density varied with tree size for 14 of 24 species, generally increasing with size. For 18 of 24 species, the correlations of leaf mass per area and an index of photosynthetic investment (PI) with biomass growth was stronger than with diameter growth rate. Juveniles did not show stronger relationships than adults but biomass growth adding up with seed production showed stronger relationships with PI than biomass growth alone for three of eight species. Synthesis. Thus, our study helps resolve a paradox of trait‐based ecology, that is, weak growth—trait relationships, as stronger relationships emerged when accounting for more sources of intraspecific, among‐tree variation in resource allocation.

Exotic tree species,though widely used in forestry and restoration projects,pose great threats to local ecosystems.They need to be replaced with native species from natural forests.We hypothesized that natural forests contain large,fast-growing,dominant native tree species that are suitable for specific topographic conditions in forestry.We tested this hypothesis using data from a 50-ha forest dynamics plot in subtropical China.We classified the plot into the ridge,slope,and valley habitats and found that 34/87 species had significant associations with at least one topographic habitat.There were 90 tree species with a maximum diameter≥30 cm,and their abundances varied widely in all habitat types.In all habitat types,for most species,rate of biomass gain due to recruitment was <1 % of its original biomass,and rate of biomass gain due to tree growth was between 1 and 5% of its original biomass.For most species,biomass loss due to tree mortality was not significantly different than biomass gain due to recruitment,but the resulting net biomass increment rates did not significantly differ from zero.The time required to reach a diameter of 30 cm from 1 cm diameter for Altingia chinensis in the slope habitat,for Quercus chungii and Morella rubra in the ridge habitat and for Castanopsis carlesii in all habitats could be as short as 30 years in our simulations based on actual distributions of tree growth observed in the forest.Principal component analyses of maximum diameter,abundance and net biomass increment rates suggested several species were worthy of further tests for use in forestry.Our study provides an example for screening native tree species from natural forests for forestry.Because native tree species are better for local ecosystems,our study will also contribute to biodiversity conservation in plantations.

Recent climate change has been shown to alter aspects of forest plant demography, such as growth and mortality, but less attention has been focused on how climate change alters the reproduction of plant populations through time. We hypothesized that the plant seed production would respond to climate change, and that the response would differ according to plant life form and functional traits. We tested this hypothesis by examining climate change from 2005 to 2020 and by determining the temporal trends of seed rain and seed production from plants with different life forms (e.g., herbs, vines, trees, palms) and of tree species with different statures as well as leaf, seed and wood traits during 2014-2020. We also tested the correlation between meteorological variables and time series of seed rain using cross correlation analysis. We found increasing wetness (lower vapor pressure deficit) through time but with decreasing minimum relative humidity, which is a pattern consistent with trends seen in many other parts of the world. During the study period, seed production of shrubs and relative contribution of woody vines to total seed rain decreased, while relative contribution of palms to total seed rain and tree species with more conservative leaf traits increased their contribution to total seed rain. Overall, these trends were well explained by the trends of meteorological variables and the responses of these life forms to climate change in previous studies. Additionally, the increasingly conservative leaf traits were also consistent with shifts in traits following recovery from disturbance. Our results suggest that a trait-based approach may help to unveil trends that are not readily apparent by examining seed counts alone. The compositional change found in the seed rain may indicate future shifts in forest species composition and should be incorporated into future studies of forest modelling and projections under climate change.

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.

1. How the dramatic vertical environmental gradients in closed canopy forests shape intraspecific variation in the functional traits of tree species and their ecological strategies is not well understood. In an Asian subtropical forest, we tested the hypothesis that, because species' maximum height and shade tolerance determine the lifetime environmental variation of a tree, they should be correlated with the magnitude of intraspecific variation in leaf traits and how strongly it depends on tree size. 2. We collected data on three vertical environmental variables, tree size and four leaf traits of 3,880 trees of 24 species in a subtropical forest. Air temperature and relative humidity displayed linear, and insolation displayed nonlinear, variation with height above-ground. Intraspecific trait variation (ITV) varied significantly among species, for all but one understorey tree species, and also varied with tree size for at least one trait. Many trait-size relationships were nonlinear with inflection points near the height where insolation dramatically increased. While ITV did not correlate with species' maximum height nor shade tolerance, the amount of ITV explained by size (SDTV) and the rate of change in trait expression with size did. 3. Greater ITV is thought to be associated with greater environmental heterogeneity, and yet strong evidence supporting this has not always been found. Our findings shed new light on how trait plasticity is phenotypically integrated with tree species' ecological strategy by pointing to the importance of accounting for tree size, since SDTV, rather than ITV, was associated with strategy variation in maximum height and shade tolerance. 4. Our study improves understanding of tree size's effect on leaf trait expression, and implies that SDTV is not only a key mechanism promoting interspecific variation in tree stature, contributing to species coexistence via vertical niche partitioning, but is also likely to influence the effects of climate change on forests by constraining tree responses to vertical environmental gradients.

Typhoons are having an increasingly severe and widespread impact on forest ecosystems around the world due to climate change. However, few studies have examined the impacts of strong typhoons on subtropical evergreen broadleaved forests, particularly in rare old-growth forests. Here, using a 20 ha permanent subtropical forest plot in Guangdong Province, southern China, the impact of super Typhoon Mangkhut on secondary and old-growth subtropical evergreen broadleaved forests was quantitatively investigated and compared. The old-growth forest was damaged more than twice as much as the secondary forest, as measured by the proportion of the basal area of damaged trees. Forest structure and composition played a significant role in determining the vulnerability of forests to powerful typhoons. This study advances knowledge about how old-growth forests respond to global climate change.

Community assembly in natural communities is commonly explained by stochastic and niche-based processes such as environmental filtering and biotic interactions. Many studies have inferred the importance of these processes using a trait-based approach, however, there are still unknowns around what factors affect the importance of different assembly processes in natural communities. In this study, the trait dispersion patterns of 134 species were examined across different functional traits, habitat types, ontogenetic stages and spatial scales from a 20-ha Dinghushan Forest Dynamic Plot in China. The results showed that (1) functional traits related to productivity such as specific leaf area and leaf area mainly showed functional clustering, indicating these two functional traits were more affected by environmental filtering. However, trait dispersion patterns depended on more than the ecological significances of functional traits. For example, trait dispersions of leaf dry matter content, leaf thickness and maximum height did not show consistent patterns across habitat types and ontogenetic stages, suggesting more complex mechanisms may operate on these traits; (2) the trait dispersion varied with the habitat types and ontogenetic stages. Specifically, we found that habitat types only affected the strength of trait dispersions for all the five traits, but ontogenetic stages influenced both the strength and direction of trait dispersions, which depended on the traits selected; (3) the relative importance of soil, topography and space to trait dispersion varied with ontogenetic stages. Topography and space were more important for trait dispersion of saplings but soil was more important for trait dispersion of adults; (4) biotic interactions dominated community assembly at smaller spatial scales but environmental filtering dominated community assembly at larger spatial scales. Overall, the results highlight the importance of functional traits, habitat types, ontogenetic stages and spatial scales to community assembly in natural communities.

The competition-colonization trade-off, by which species can partition spatial niches, is a potentially important mechanism allowing the maintenance of species diversity in plant communities. We examined whether there was evidence for this trade-off among tree species in a subtropical forest and how it correlated with eight functional traits. We developed and estimated a metric for colonization ability that incorporates both fecundity and seed dispersal based on seed trap data and the sizes and distributions of adult trees. Competitive ability was estimated as survival probability under high crowding conditions based on neighborhood models. Although we found no significant relationship between colonization and competitive abilities, there was a significant negative correlation between long distance dispersal ability and competitive ability at the 5 cm size class. Colonizers had traits associated with faster growth, such as large leaves and low leaf lamina density, whereas competitors had traits associated with higher survival, such as dense wood. Our results imply that any trade-off between competition and colonization may be more determined by dispersal ability than by fecundity, suggesting that seed dispersal is an important contributor to diversity maintenance. Future work should test how competitive ability covaries with the components of colonization ability, as we did here.

Niche‐driven effects on demographic processes generated in response to habitat heterogeneity partly shape local distributions of species. Thus, tree distributions are commonly studied in relation to habitat conditions to understand how niche differentiation contributes to species coexistence in forest communities. Many such studies implicitly assume that local abundance reflects habitat suitability, and that abundance is relatively stable over time. We compared models based on abundance with those based on demographic performance for making inferences about habitat association for 287 tree species from three large dynamic plots located in tropical, subtropical and temperate forests. The correlation between the predictions of the abundance‐based models and the demography‐based models varied widely, with correlation coefficients ranging nearly from −1 to 1.This suggests that the two types of models capture different information about species–habitat associations. Demography‐based models evaluate habitat quality by focusing on population processes and thus should be preferred for understanding responses of tree species to habitat conditions, especially when habitat conditions are changing and species–habitat interactions cannot be considered to be at equilibrium.

BACKGROUND:Ecologists have been monitoring community dynamics with the purpose of understanding the rates and causes of community change. However, there is a lack of monitoring of community dynamics from the perspective of phylogeny.METHODS/PRINCIPLE FINDINGS:We attempted to understand temporal phylogenetic turnover in a 50 ha tropical forest (Barro Colorado Island, BCI) and a 20 ha subtropical forest (Dinghushan in southern China, DHS). To obtain temporal phylogenetic turnover under random conditions, two null models were used. The first shuffled names of species that are widely used in community phylogenetic analyses. The second simulated demographic processes with careful consideration on the variation in dispersal ability among species and the variations in mortality both among species and among size classes. With the two models, we tested the relationships between temporal phylogenetic turnover and phylogenetic similarity at different spatial scales in the two forests. Results were more consistent with previous findings using the second null model suggesting that the second null model is more appropriate for our purposes. With the second null model, a significantly positive relationship was detected between phylogenetic turnover and phylogenetic similarity in BCI at a 10 m×10 m scale, potentially indicating phylogenetic density dependence. This relationship in DHS was significantly negative at three of five spatial scales. This could indicate abiotic filtering processes for community assembly. Using variation partitioning, we found phylogenetic similarity contributed to variation in temporal phylogenetic turnover in the DHS plot but not in BCI plot.CONCLUSIONS/SIGNIFICANCE:The mechanisms for community assembly in BCI and DHS vary from phylogenetic perspective. Only the second null model detected this difference indicating the importance of choosing a proper null model.

Habitat association test has been regarded as an effective way to evaluate the relative role of niche differentiation in a community. Topographical attributes are often selected as surrogates of niche processes. However, the inference for relative role of niche differentiation is likely problematic if the spatial dependence of plant community on underlying spatiallystructured topographic variables is not accounted for. In this study, we used the torus shift and principal component analysis (PCA) to resolve this problem, and tested the habitat associations by adjusted-SD test in a sub-tropical evergreen broad-leaved forest in south China. The result revealed that minority of 100 common species were specialist, among which 8 species associated with first two PC axes (accounted for 98% of total eigenvalue and contributed mainly by mean elevation and aspect) and 22 species associated with last two PC axes (contributed by slope and convexity). In conclusion, we found the niche processes represented by topographical attributes play a limited role in the Dinghushan sub-tropical evergreen broad-leaved forest plot. Further study should include more habitat variables to examine the habitat associations.

Summary The relationship between species richness and ecosystem function, as measured by productivity or biomass, is of long‐standing theoretical and practical interest in ecology. This is especially true for forests, which represent a majority of global biomass, productivity and biodiversity. Here, we conduct an analysis of relationships between tree species richness, biomass and productivity in 25 forest plots of area 8–50 ha from across the world. The data were collected using standardized protocols, obviating the need to correct for methodological differences that plague many studies on this topic. We found that at very small spatial grains (0.04 ha) species richness was generally positively related to productivity and biomass within plots, with a doubling of species richness corresponding to an average 48% increase in productivity and 53% increase in biomass. At larger spatial grains (0.25 ha, 1 ha), results were mixed, with negative relationships becoming more common. The results were qualitatively similar but much weaker when we controlled for stem density: at the 0.04 ha spatial grain, a doubling of species richness corresponded to a 5% increase in productivity and 7% increase in biomass. Productivity and biomass were themselves almost always positively related at all spatial grains. Synthesis. This is the first cross‐site study of the effect of tree species richness on forest biomass and productivity that systematically varies spatial grain within a controlled methodology. The scale‐dependent results are consistent with theoretical models in which sampling effects and niche complementarity dominate at small scales, while environmental gradients drive patterns at large scales. Our study shows that the relationship of tree species richness with biomass and productivity changes qualitatively when moving from scales typical of forest surveys (0.04 ha) to slightly larger scales (0.25 and 1 ha). This needs to be recognized in forest conservation policy and management.

Tree size distributions have long been of interest to ecologists and foresters because they reflect fundamental demographic processes. Previous studies have assumed that size distributions are often associated with population trends or with the degree of shade tolerance. We tested these associations for 31 tree species in a 20 ha plot in a Dinghushan south subtropical forest in China. These species varied widely in growth form and shade-tolerance. We used 2005 and 2010 census data from that plot. We found that 23 species had reversed J shaped size distributions, and eight species had unimodal size distributions in 2005. On average, modal species had lower recruitment rates than reversed J species, while showing no significant difference in mortality rates, per capita population growth rates or shade-tolerance. We compared the observed size distributions with the equilibrium distributions projected from observed size-dependent growth and mortality. We found that observed distributions generally had the same shape as predicted equilibrium distributions in both unimodal and reversed J species, but there were statistically significant, important quantitative differences between observed and projected equilibrium size distributions in most species, suggesting that these populations are not at equilibrium and that this forest is changing over time. Almost all modal species had U-shaped size-dependent mortality and/or growth functions, with turning points of both mortality and growth at intermediate size classes close to the peak in the size distribution. These results show that modal size distributions do not necessarily indicate either population decline or shade-intolerance. Instead, the modal species in our study were characterized by a life history strategy of relatively strong conservatism in an intermediate size class, leading to very low growth and mortality in that size class, and thus to a peak in the size distribution at intermediate sizes.

Seedling recruitment can be influenced by seed dispersal, conspecific density dependence, and environmental factors. These forces are variant in space. In this study, seedling recruitment was investigated by the inverse modeling method. The inverse modeling framework here was made up of two components: a conspecific effect and a declining function. Power functions (P) and constant conspecific (C) effects were tried. Two types of declining functions were tried: isotropic (I) and anisotropic (A). Thus, the combination of conspecific effect and declining function generated four candidate models: PI, PA, CI, CA. These four models were used to study the seedling recruitment of 13 species in a 20 ha forest plot in subtropical China. It was found that PI, PA, CI, CA are the best models for two, three, five, and three species, respectively. Negative exponents in P were found in three species, which may indicate negative density-dependent mortality. Among those species that supported an anisotropic component, all moderately shade-tolerant and shade-tolerant species except Calophyllum membranaceum had higher possibilities of successful recruitment if their altitudes were relatively low, consistent with their ecological niches. The shade intolerant species, Castanopsis fissa produces seeds weighing 6–250 times more than other species. Yet, its seedling recruitment was more successful at higher altitudes, which again was consistent with its ecological niche. Our research indicated that it is necessary to take anisotropic forces into account when investigating seed dispersal and seedling recruitment in regions with complex topography, and that the niche-based processes and density-dependent mortality at least play some part in constructing the seedling distribution pattern.

为了解鼎湖山常绿阔叶林树木幼苗的组成、分布及高度结构,在鼎湖山20 ha动态监测样地(简称DHS)内布置了149个种子雨收集器,并在周围设置了幼苗小样方.2008年31月完成了幼苗调查,共调查到2,632株.采用多元线性回归方法分析了9个树种幼苗多度与6个变鼍之间的关系.这6个变量包括种子雨收集器10 m内DBH≥1 cm同种个体的个体数、胸高断面积之和,以及地形的凹凸度、坡度、坡向和海拔.结果表明影响幼苗多度的因素随树种不同而不同.其中3个树种的幼苗多度只与地形变量有关,4个树种幼陌多度同时受到地形和同种个体多度的影响,1个树种的幼苗多度只与同种个体有关,1个树种幼苗多度与所有变量的关系都不显著.除谷木(Memecylon ligustrifolium)外,10 m范围内同种个体的多度和胸高断面积的偏回归系数一旦显著皆为正值,即幼苗多度随同种个体数或同种胸高断面积增大而增大.本研究为扩散限制和生态位理论提供了间接的证据.

AbstractQuestionsSpecies co‐existence may be achieved by limited dispersal due to the reduced chance of inter‐specific competition. But the timing of seed release also provides clues for species co‐existence because asynchronous reproduction can alleviate inter‐specific competition for dispersal agents, while synchronous reproduction can facilitate overall seed dispersal. How strong is seed dispersal limitation, do co‐existing species release seeds synchronously or asynchronously, and what is the relationship between seed production and main meteorological measures?LocationA 25‐ha plot in a temperate forest, Changbai Mountain, Northeast China.MethodsWe calculated Jaccard coefficients between seed rain composition and neighbouring adult tree composition, analysed long‐term seed rain dynamics for both the whole community and different species, and regressed seed rain density with meteorological measures using autoregressive models.ResultsThe Jaccard coefficient dropped sharply as neighbourhood radius increased to about 10 m, indicating severe dispersal limitation. Both synchrony and asynchrony in seed release were observed: most species released mature seeds synchronously from August to November, with small segregations in time; one species released seeds in Jun. Bimodal and unimodal seasonal dynamics of seed rain were observed and some species released seeds beyond the main fruiting seasons. The seasonal dynamics of seed release might be driven by different strategies of seed dispersal. Seed rain density is significantly positively related to temperature and precipitation, with a 2‐mo time lag.ConclusionsBoth dispersal limitation and timing of seed release by co‐existing species may contribute to maintenance of diversity of this forest, but variations in temperature and precipitation considerably alter seed rain density.