Search

Abstract Soil carbon (C) cycling plays a critical role in regulating global C budget and atmospheric CO2 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, Q10) 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 Q10 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 Q10 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 Q10. 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 Q10. The variation in Q10 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.

Abstract Keystone species are more important than others for community dynamics and stability. Keystone species can be identified and evaluated by their centrality (i.e., a relative ranking of the topological positional importance of a species) in ecological networks. Studies of node centrality of plant–fungus bipartite networks, for example, have identified the keystone species that are important for maintaining network structure and stability. However, the underlying drivers of the importance of species in a network have rarely been examined. We assessed the centrality (degree, closeness, and betweenness) of plant and fungal species in a plant–ectomycorrhizal fungus network in a subtropical forest in southern China. Based on the phylogenies of plants and fungi and plant traits, we explored ecological factors that led to a species taking a central position or not. We found one plant species (Ternstroemia gymnanthera) and four species of ectomycorrhizal fungi (Russula citrina, Scleroderma sp., and two Cenococcum sp.) were characterized by the highest centrality of degree, closeness, and betweenness among the bipartite network nodes and thus played key roles in maintaining network structure. Centrality for fungi (not for plants) was phylogenetically constrained. Plant traits and abundance together explained 46.36%, 46.0%, and 43.7% of variation in the centrality of degree, closeness, and betweenness of plant species in the bipartite network, respectively. When plant or fungal species were sequentially removed on the order of higher to lower centrality, network was less stable than randomly removed. We suggest that abundance and traits determine the positional importance of plant species in a network. This work helps understand how plant–fungus association networks will respond to species extinction and changes in species abundance and functional traits due to habitat fragmentation and human activities.

Abstract One mechanism proposed to explain high species diversity in tropical systems is strong negative conspecific density dependence (CDD), which reduces recruitment of juveniles in proximity to conspecific adult plants. Although evidence shows that plant-specific soil pathogens can drive negative CDD, trees also form key mutualisms with mycorrhizal fungi, which may counteract these effects. Across 43 large-scale forest plots worldwide, we tested whether ectomycorrhizal tree species exhibit weaker negative CDD than arbuscular mycorrhizal tree species. We further tested for conmycorrhizal density dependence (CMDD) to test for benefit from shared mutualists. We found that the strength of CDD varies systematically with mycorrhizal type, with ectomycorrhizal tree species exhibiting higher sapling densities with increasing adult densities than arbuscular mycorrhizal tree species. Moreover, we found evidence of positive CMDD for tree species of both mycorrhizal types. Collectively, these findings indicate that mycorrhizal interactions likely play a foundational role in global forest diversity patterns and structure.

Microorganisms can influence plant growth and health, ecosystem functioning, and stability. Community and network structures of mangrove phyllosphere fungi have rarely been studied although mangroves have very important ecological and economical values. Here, we used high throughput sequencing of the internal transcribed spacer 2 (ITS2) to assess epiphytic and endophytic phyllosphere fungal communities of six true mangrove species and five mangrove associates. Totally, we obtained 1,391 fungal operational taxonomic units (OTUs), including 596 specific epiphytic fungi, 600 specific endophytic fungi, and 195 shared fungi. The richness and community composition differed significantly for epiphytes and endophytes. Phylogeny of the host plant had a significant constraint on epiphytes but not endophytes. Network analyses showed that plant–epiphyte and plant–endophyte networks exhibited strong specialization and modularity but low connectance and anti-nestedness. Compared to plant–endophyte network, plant–epiphyte network showed stronger specialization, modularity, and robustness but lower connectance and anti-nestedness. These differences in community and network structures of epiphytes and endophytes may be caused by spatial niche partitioning, indicating their underlying ecological and environmental drivers are inconsistent. We highlight the important role of plant phylogeny in the assembly of epiphytic but not endophytic fungal communities in mangrove ecosystems.

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.

The potential patterns and processes of ecosystem multifunctionality (EMF) across global ecosystems are largely unknown, which limits our understanding of how ecosystems respond to drivers. Here we compile a global dataset that consists of 973 unique sites across the forest, grassland, and shrub ecosystems. We identify a critical global pattern of hump-shaped EMF relationship with mean annual precipitation at a threshold of ∼671 mm, where low and high precipitation patterns are discriminated. We find that climatic and soil factors jointly drive the EMF in low precipitation areas, and climatic factors dominate the EMF in high precipitation regions. However, when comparing across the three dominant ecosystems and precipitation regions, the key driver in EMF differs substantially. Specifically, climatic and soil factors dominate the EMF of low and high precipitation regions across forest ecosystems, respectively. Climatic drivers dominate the EMF under different precipitation conditions across grassland and shrub ecosystems. Overall, our findings highlight the importance of climatic and soil drivers on EMF, which should be considered in ecosystem stability models in response to global climate and land-use change scenarios.

The relationship of mycorrhizal associations with latitudinal gradients in tree beta-diversity is unexplored. Using a global dataset approach, this study examines how trees with arbuscular mycorrhizal and ectomycorrhizal associations contribute to latitudinal beta-diversity patterns and the environmental controls of these patterns.

A tight association between microbial function and taxonomy is the basis of functional prediction based on taxonomy, but such associations have been controversial in water biomes largely due to the probable prevalence of functional redundancy. However, previous studies on this topic used a relatively coarse resolution of ecosystem functioning, potentially inflating the estimated functional redundancy. Thus, a comprehensive evaluation of the association between high-resolution functional traits and taxonomic diversity obtained from fresh and saline water metagenomic data is urgently needed. Here, we examined 938 functionally and taxonomically annotated water metagenomes obtained worldwide to scrutinize the connection between function and taxonomy, and to identify the key driver of water metagenomes function or taxonomic composition at a global scale. We found that pairwise similarity of function was significantly associated with taxonomy, though taxonomy had higher global dissimilarity than function. Classification into six water biomes resulted in greater variation in taxonomic compositions than functional profiles, as the key regulating factor was salinity. Fresh water microbes harbored distinct functional and taxonomic structures from microbes in saline water biomes, despite that taxonomy was more susceptible to gradient of geography and climate than function. In summary, our results find a significant relationship between taxonomic diversity and microbial functioning in global water metagenomes, although microbial taxonomic compositions vary to a larger extent than functional profiles in aquatic ecosystems, suggesting the possibility and necessity for functional prediction of microorganisms based on taxonomy in global aquatic ecosystems.

Anthropogenic disturbances and global climate change are causing large-scale biodiversity loss and threatening ecosystem functions. However, due to the lack of knowledge on microbial species loss, our understanding on how functional profiles of soil microbes respond to diversity decline is still limited. Here, we evaluated the biotic homogenization of global soil metagenomic data to examine whether microbial functional structure is resilient to significant diversity reduction. Our results showed that although biodiversity loss caused a decrease in taxonomic species by 72%, the changes in the relative abundance of diverse functional categories were limited. The stability of functional structures associated with microbial species richness decline in terrestrial systems suggests a decoupling of taxonomy and function. The changes in functional profile with biodiversity loss were function-specific, with broad-scale metabolism functions decreasing and typical nutrient-cycling functions increasing. Our results imply high levels of microbial physiological versatility in the face of significant biodiversity decline, which, however, does not necessarily mean that a loss in total functional abundance, such as microbial activity, can be overlooked in the background of unprecedented species extinction.

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.

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.

To measure intraspecific and interspecific interaction coefficients among tree species is the key to explore the underlying mechanisms for species coexistence and biodiversity maintenance in forests. Through the response surface experimental design, we established a long-term field experiment by planting 27,300 seedlings of four tree species (Erythrophleum fordii, Pinus massoniana, Castanopsis fissa, and Castanopsis carlesii) in 504 plots in different species combinations (six pairwise combinations of four species), abundance proportions (five abundance proportions of two species, i.e. A: B = 1:0, 3:1, 1:1, 1:3, 0:1), and stand densities (25, 36, 64, and 100 seedlings per plot). In this initial report, we aimed to quantify the relative importance of biotic and abiotic factors on seedling survival at the early stage of growth, which is a critical period for seedling establishment. We found that plot-level seedling survival rate was determined by species combination and their abundance proportion rather than stand density. At the individual level, individual survival probability was mainly explained by species identity, initial seedling size, and soil conditions rather than neighborhood competition. Our study highlights that the seedling intrinsic properties may be the key factors in determining seedling survival rate, while neighborhood effects were not yet prominent at the seedling life stage.

Climate change could alter plant aboveground and belowground resource allocation. Compared with shoots, we know much less about how roots, especially root system architecture (RSA) and their interactions, may respond to temperature changes. Such responses could have great influence on species'acquisition of resources and their competition with neighbors. We used a gel-based transparent growth system to in situ observe the responses of RSA and root interactions of three common subtropical plant species seedlings in Asia differing in growth forms (herb, shrub, and tree) under a wide growth temperature range of 18–34°C, including low and supra-optimal temperatures. Results showed that the RSA, especially root depth and root width, of the three species varied significantly in response to increased temperature although the response of their aboveground shoot traits was very similar. Increased temperature was also observed to have little impact on shoot/root resource allocation pattern. The variations in RSA responses among species could lead to both the intensity and direction change of root interactions. Under high temperature, negative root interactions could be intensified and species with larger root size and fast early root expansion had competitive advantages. In summary, our findings indicate that greater root resilience play a key role in plant adapting to high temperature. The varied intensity and direction of root interactions suggest changed temperatures could alter plant competition. Seedlings with larger root size and fast early root expansion may better adapt to warmer climates.

The recovery of North American forests is likely to impact their capacity as a carbon sink. Here, Zhu et al. show a growth in aboveground biomass in various climate change scenarios, with these forests expected to sequester no more than 22% more carbon than current levels by the 2080s.

Abstract In an era of global environmental change, understanding how disturbance affects the dynamics of ecological communities is crucial. However, few studies have theoretically explored the potential influence of disturbance including both intensity and frequency on compositional change over time in communities with stage structure. A spatially explicit, individual‐based model was constructed incorporating the various demographic responses to disturbance of plants at two different growth stages: seedlings and adults. In the model, we assumed that individuals within each stage were demographically equivalent (neutral) but differed between stages. We simulated a common phenomenon that seedlings suffered more from disturbance such as grazing and fire than adults. We showed how stage‐structured communities of seedlings and adults responded to disturbance with various levels of disturbance frequency and intensity. In “undisturbed” simulations, the relationship between average species abundance (defined here as the total number of individuals divided by species richness) and community composition turnover (measured by the Bray–Curtis similarity index) was asymptotic. However, in strongly “disturbed” simulations with the between‐disturbance intervals greater than one, this relationship became unimodal. Stage‐dependent response to disturbance underlay the above discrepancy between undisturbed and disturbed communities.

Environmental change can have indirect effects on populations by altering the outcome of competitive interactions. Here, Chu et al. show that although direct effects dominate the responses of grassland species to climate perturbations, indirect effects could be greater among species with smaller niche differences.

Plant succession is regulated by a combination of abiotic and biotic factors. However, previous studies of biotic drivers have focused overwhelmingly on direct pairwise species interactions, ignoring the likely prevalent higher-order interactions (HOIs) in natural systems. Climate also plays a significant role in determining successional dynamics with both direct effects and indirect effects via altered biotic interactions. Here we explored the relative effects of direct species interactions, HOIs, climate, and their interactions on population dynamics of herbaceous plants during 50 years of post-agricultural secondary succession and tested whether the inclusion of HOIs and climate data improved forecasts of population dynamics. Direct intraspecific interactions were competitive and prevalent across the 90 herbaceous plants examined, while direct interspecific interactions only affected populations of 29% species. HOIs, mainly arose from intraspecific HOIs of conspecifics, were mostly positive and thus largely mitigated the competitive effects of direct intraspecific interactions. Species with lower peak cover experienced stronger intraspecific competition and positive intraspecific HOIs of conspecifics. Direct interspecific interactions had neutral or facilitative effects on species with lower peak cover, and tended to have competitive effects on species with higher peak cover. Climate simultaneously influenced population dynamics both directly and indirectly via altered species interactions. Forecast performance was significantly improved with the inclusion of HOIs or climate for about half and one-third of species, respectively. Our study emphasizes the importance of HOIs, which largely mitigated direct competitive effects on population dynamics of herbaceous plants during succession. Teasing apart HOIs from direct species interactions substantially refined our understanding of successional dynamics of herbaceous plants and improved the accuracy of forecasting population dynamics during succession in a changing world.

Shade tolerance, the minimum light requirement for plant survival, is a key trait for understanding community assembly and forest dynamics. However, it is poorly defined for tree species to date. Current methods of measuring shade tolerance vary considerably in their performance. For instance, some measures of shade tolerance are unreliable except under some specific conditions. Therefore, it is necessary to compare the performance of these methods to provide guidance of choosing appropriate shade tolerance measures in future studies. We collected a large dataset of light traits and other life history traits for 137 understory wood species in a subtropical forest and tested the performance of five commonly used shade-tolerance indices. Results showed that all the shade-tolerance measures, except the low-light abundance index, performed poorly in distinguishing and ranking shade tolerance of the tested species. The shade tolerance quantified by the low-light abundance was consistent with empirical classification of shade-tolerance/intolerance groups and successional seral stages of species. Comparison of the shade tolerance between trees of different diameter at breast height (DBH) or height classes further confirmed the reliability of low-light abundance. We conclude that low-light abundance is the most objective and practical of the five most commonly-used methods for measuring and ranking shade tolerance of understory wood species in our study forest, and likely in other forests as well. The simplicity of the method should greatly facilitate the assessment of light niche differentiation between species and thus contribute to understanding coexistence of tree species in forests.

The directionality of the response of gross primary productivity (GPP) to climate has been shown to vary across the globe. This effect has been hypothesized to be the result of the interaction between multiple bioclimatic factors, including environmental energy (i.e. temperature and radiation) and water availability. This is due to the tight coupling between water and carbon cycling in plants and the fact that temperature often drives plant water demand. Using GPP data extracted from 188 sites of FLUXNET2015 and observation-driven terrestrial biosphere models (TBMs), we disentangled the confounding effects of temperature, precipitation and carbon dioxide on GPP, and examined their long-term effects on productivity across the globe. Based on the FLUXNET2015 data, we observed a decline in the positive effect of temperature on GPP, while the positive effects of precipitation and CO _2 were becoming stronger during 2000–2014. Using data derived from TBMs between 1980 and 2010 we found similar effects globally. The modeled data allowed us to investigate these effects more thoroughly over space and time. In arid regions, the modeled response to precipitation increased since 1950, approximately 30 years earlier than in humid regions. We further observed the negative effects of summer temperature on GPP in arid regions, suggesting greater aridity stress on productivity under global warming. Our results imply that aridity stress, triggered by rising temperatures, has reduced the positive influence of temperature on GPP, while increased precipitation and elevated CO _2 may alleviate negative aridity impacts.

The correspondence between species distribution and the environment depends on species' ability to track favorable environmental conditions (via dispersal) and to maintain competitive hierarchy against the constant influx of migrants (mass effect) and demographic stochasticity (ecological drift). Here we report a simulation study of the influence of landscape structure on species distribution. We consider lottery competition for space in a spatially heterogeneous environment, where the landscape is represented as a network of localities connected by dispersal. We quantified the contribution of neutrality and species sorting to their spatial distribution. We found that neutrality increases and the strength of species-sorting decreases with the centrality of a community in the landscape when the average dispersal among communities is low, whereas the opposite was found at elevated dispersal. We also found that the strength of species-sorting increases with environmental heterogeneity. Our results illustrate that spatial structure of the environment and of dispersal must be taken into account for understanding species distribution. We stress the importance of spatial geographic structure on the relative importance of niche vs. neutral processes in controlling community dynamics.

Based on regional-scale studies, aboveground production and litter decomposition are thought to positively covary, because they are driven by shared biotic and climatic factors. Until now we have been unable to test whether production and decomposition are generally coupled across climatically dissimilar regions, because we lacked replicated data collected within a single vegetation type across multiple regions, obfuscating the drivers and generality of the association between production and decomposition. Furthermore, our understanding of the relationships between production and decomposition rests heavily on separate meta-analyses of each response, because no studies have simultaneously measured production and the accumulation or decomposition of litter using consistent methods at globally relevant scales. Here, we use a multi-country grassland dataset collected using a standardized protocol to show that live plant biomass (an estimate of aboveground net primary production) and litter disappearance (represented by mass loss of aboveground litter) do not strongly covary. Live biomass and litter disappearance varied at different spatial scales. There was substantial variation in live biomass among continents, sites and plots whereas among continent differences accounted for most of the variation in litter disappearance rates. Although there were strong associations among aboveground biomass, litter disappearance and climatic factors in some regions (e.g. U.S. Great Plains), these relationships were inconsistent within and among the regions represented by this study. These results highlight the importance of replication among regions and continents when characterizing the correlations between ecosystem processes and interpreting their global-scale implications for carbon flux. We must exercise caution in parameterizing litter decomposition and aboveground production in future regional and global carbon models as their relationship is complex.

It has been demonstrated that the interplay between negative and positive interactions simultaneously shapes community structure and composition. However, few studies have attempted to examine the effect of facilitation on compositional changes in communities through time. Additionally, due to the difficulties in collecting the long-term data, it would be useful to indicate the rate of temporal turnover using a readily obtainable metric. Using an individual-based model incorporating plant strategies, we examined the role of facilitation on the temporal turnover of communities located at different positions along an environmental gradient for three model scenarios: CM without facilitation; CFM-U, a unimodal relationship between facilitation and environmental severity; and CFM-L, a positively linear relationship between facilitation and environmental severity. Our results demonstrated that facilitation could increase, decrease or have no remarkable effect on temporal turnover. The specific outcome depended on the location of the focal community across the environmental gradient and the model employed. Compared with CM, the inclusion of positive interactions (i.e. CFM-U and CFM-L), at intermediate environmental stress levels (such as S = 0.7 and 0.8) resulted in lower Bray-Curtis similarity values; at other severity levels, facilitation slowed down (such as S = 0.3 and 0.4 at low to medium stress levels, and S = 0.9 at high stress levels) or had only a subtle effect (such as at S = 0.1) on temporal turnover. We also found that the coefficient of variation (CV) in species abundances and the rate of temporal variability showed a significant quadratic relationship. Our theoretical analysis contributes to the understanding of factors driving temporal turnover in biotic communities, and presents a potential metric (i.e. CV in species abundances) assessing the consequences of ongoing environmental change on community structure.

Repeatability of community composition has been a critical aspect for community structure, which is closely associated with community stability, predictability, conservation biology and ecological restoration. It has been shown that both immigration and local dispersal limitation can affect the community composition in both neutral and niche model. Hence, we use a spatially explicit individual-based model to investigate the potential influence of immigration rate and strength of local dispersal limitation on repeatability in both neutral and niche models. Similarity measures are used to quantify repeatability. We examine the repeatability of community composition among replicate communities (which means the same community repeats many times), and between niche and neutral replicate communities. We find the correlation between repeatability and immigration rate is positive in the neutral model and an inverted unimodal in the niche model. The correlation between repeatability and local dispersal distance is positive in the niche model and negative in the neutral model. High repeatability between niche communities and neutral communities is observed with high immigration rates or when high local dispersal distance appears in the niche model or low local dispersal distance in the neutral model. Our results show that repeatability of community composition is not only dependent on the types of community models (niche vs. neutrality) but also strongly determined by immigration rates and local dispersal limitation.

The relationship between species richness and evenness across communities remains an unsettled issue in ecology from both theoretical and empirical perspectives. As a result, we do not know the mechanisms that could generate a relationship between species richness and evenness, and how this responds to spatial scale. Here we examine the relationship between species richness(S) and evenness (Pielou's J' evenness) using a chronosequence of successional sub-alpine meadow communities in the eastern Qinghai-Tibetan Plateau. These meadows range from natural community (never farmed), to those that have been protected from agricultural exploitation for periods ranging from 1 to 10 years. A total of 30 sampling quadrats with size of 0.5 m×0.5 m were laid out along two transects at each meadow. Using correlation analyses we found a consistent negative correlation between S and J' in these communities along the successional gradient at the sampling scale of 0.5 m×0.5 m. We also explored the relationship between S and J' at different sampling scales (from 0.5 m×0.5 m to10 m×10 m) using properly measured ramet-mapped data of a10 m×10 m quadrat in the natural community. We found that S was negatively corrected with J' at the scales of 0.5 m×0.5 m to 2 m×2 m, but such a relationships disappeared at relative larger scales (≥2 m×4 m). When fitting different species abundance models combined with trait-specific methods, we found that niche preemption may be the determining mechanism of species evenness along the succession gradient. Considering all results together, we can conclude that such niche differentiation and spatial scale effects may help to explain the maintenance of high species richness in sub-alpine meadow communities.