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A prominent tree species coexistence mechanism suggests host-specific natural enemies inhibit seedling recruitment at high conspecific density (negative conspecific density dependence). Natural-enemy-mediated conspecific density dependence affects numerous tree populations, but its strength varies substantially among species. Understanding how conspecific density dependence varies with species’ traits and influences the dynamics of whole communities remains a challenge. Using a three-year manipulative community-scale experiment in a temperate forest, we show that plant-associated fungi, and to a lesser extent insect herbivores, reduce seedling recruitment and survival at high adult conspecific density. Plant-associated fungi are primarily responsible for reducing seedling recruitment near conspecific adults in ectomycorrhizal and shade-tolerant species. Insects, in contrast, primarily inhibit seedling recruitment of shade-intolerant species near conspecific adults. Our results suggest that natural enemies drive conspecific density dependence in this temperate forest and that which natural enemies are responsible depends on the mycorrhizal association and shade tolerance of tree species. The Janzen-Connell hypothesis posits that seedlings may be less likely to establish near conspecifics due to shared natural enemies. Here, Jia et al. show that tree species traits determine whether fungal pathogens or insect herbivores inhibit seedling recruitment and survival in a temperate forest.

The theory of “top-down” ecological regulation predicts that herbivory suppresses plant abundance, biomass, and survival but increases diversity through the disproportionate consumption of dominant species, which inhibits competitive exclusion. To date, these outcomes have been clear in aquatic ecosystems but not on land. We explicate this discrepancy using a meta-analysis of experimental results from 123 native animal exclusions in natural terrestrial ecosystems (623 pairwise comparisons). Consistent with topdown predictions, we found that herbivores significantly reduced plant abundance, biomass, survival, and reproduction (all P < 0.01) and increased species evenness but not richness (P = 0.06 and P = 0.59, respectively). However, when examining patterns in the strength of top-down effects, with few exceptions, we were unable to detect significantly different effect sizes among biomes, based on local site characteristics (climate or productivity) or study characteristics (study duration or exclosure size). The positive effects on diversity were only significant in studies excluding large animals or located in temperate grasslands. The results demonstrate that top-down regulation by herbivores is a pervasive process shaping terrestrial plant communities at the global scale, but its strength is highly site specific and not predicted by basic site conditions. We suggest that including herbivore densities as a covariate in future exclosure studies will facilitate the discovery of unresolved macroecology trends in the strength of herbivore–plant interactions.

Forests play a key role in regulating the global carbon cycle, and yet the abiotic and biotic conditions that drive the demographic processes that underpin forest carbon dynamics remain poorly understood in natural ecosystems. To address this knowledge gap, we used repeat forest inventory data from 92,285 trees across four large permanent plots (4–25 ha in size) in temperate mixed forests in northeast China to ask the following questions: (1) How do soil conditions and stand age drive biomass demographic processes? (2) How do vegetation quality (i.e., functional trait diversity and composition) and quantity (i.e., initial biomass stocks) influence biomass demographic processes independently from soil conditions and stand age? (3) What is the relative contribution of growth, recruitment, and mortality to net biomass change? Using structural equation modeling, we showed that all three demographic processes were jointly constrained by multiple abiotic and biotic factors and that mortality was the strongest determinant on net biomass change over time. Growth and mortality, as well as functional trait diversity and the community-weighted mean of specific leaf area (CWMSLA), declined with stand age. By contrast, high soil phosphorous concentrations were associated with greater functional diversity and faster dynamics (i.e., high growth and mortality rates), but associated with lower CWMSLA and initial biomass stock. More functionally diverse communities also had higher recruitment rates, but did not exhibit faster growth and mortality. Instead, initial biomass stocks and CWMSLA were stronger predictors of biomass growth and mortality, respectively. By integrating the full spectrum of abiotic and biotic drivers of forest biomass dynamics, our study provides critical system-level insights needed to predict the possible consequences of regional changes in forest diversity, composition, structure and function in the context of global change.

Soil fertility influences plant community structure, yet few studies have focused on how this influence is affected by the type of mycorrhizal association formed by tree species within local communities. We examined the relationship of aboveground biomass (AGB) and diversity of adult trees with soil fertility (nitrogen, phosphorus, organic matter, etc.) in the context of different spatial distributions of arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) trees in a temperate forest in Northeast China. Diversity showed a positive trend along the soil fertility gradient driven mostly by a positive relationship between AM tree abundance and soil fertility. By contrast, the AGB showed a negative trend along the soil fertility gradient driven mostly by a negative relationship between EM tree AGB and soil fertility. Furthermore, the opposite trend in the AGB and tree species diversity along the soil fertility gradient led to an overall negative diversity–biomass relationship at the 50-m scale but not the 20-m scale. These results suggest that tree mycorrhizal associations play a critical role in driving forest community structure along soil fertility gradients and highlight the importance of tree mycorrhizal associations in influencing how the diversity–ecosystem function (e.g. biomass) relationships change with soil fertility.

Long-term, daily, and gap-free Normalized Difference Vegetation Index (NDVI) is of great significance for a better Earth system observation. However, gaps and contamination are quite severe in current daily NDVI datasets. This study developed a daily 0.05° gap-free NDVI dataset from 1981–2023 in China by combining valid data identification and spatiotemporal sequence gap-filling techniques based on the National Oceanic and Atmospheric Administration daily NDVI dataset. The generated NDVI in more than 99.91% of the study area showed an absolute percent bias (|PB|) smaller than 1% compared with the original valid data, with an overall R 2 and root mean square error (RMSE) of 0.79 and 0.05, respectively. PB and RMSE between our dataset and the MODIS daily gap-filled NDVI dataset (MCD19A3CMG) during 2000 to 2023 are 7.54% and 0.1, respectively. PB between our dataset and three monthly NDVI datasets (i.e., GIMMS3g, MODIS MOD13C2, and SPOT/PROBA) are only −5.79%, 4.82%, and 2.66%, respectively. To the best of our knowledge, this is the first long-term daily gap-free NDVI in China by far.

Interactions between plants and soil microbial communities underpin soil processes and forest ecosystem function, but the links between tree diversity and soil microbial diversity are poorly characterized. Differences in both the taxonomic and functional diversity of trees and microbes can shape soil nutrient status and carbon storage, but the stoichiometry of carbon and nutrients in the soil also influences resource availability to plant and microbial communities. Given the key role of resource availability in plant–soil interactions, we hypothesized that relationships between tree diversity metrics and soil bacterial or fungal diversity are mediated by soil stoichiometry. To test our hypothesis, we measured tree diversity metrics (tree species richness, functional trait diversity and functional trait composition) and soil stoichiometry in a temperate forest in China, and we determined soil microbial diversity by Illumina sequencing. We used structural equation models to assess the relationships between tree diversity metrics and soil bacterial or fungal diversity and to evaluate the influence of soil stoichiometry. Overall, microbial diversity was strongly related to soil stoichiometry, whereby fungal diversity was associated with high soil N/P ratios, whereas bacterial diversity was related to high soil C/P ratios. Soil bacterial and fungal diversity were more closely related to tree functional trait diversity and composition than to tree species richness, and the links between tree and soil microbial diversity were mediated by soil stoichiometry. The strong links between tree functional traits, soil stoichiometry and soil bacteria or fungi suggest that resource quality plays a key role in plant–microbial interactions. Our results highlight the importance of nutrient stoichiometry in linkages between tree functional diversity and soil microbial diversity.

Biodiversity can be measured by taxonomic, phylogenetic, and functional diversity. How ecosystem functioning depends on these measures of diversity can vary from site to site and depends on successional stage. Here, we measured taxonomic, phylogenetic, and functional diversity, and examined their relationship with biomass in two successional stages of the broad-leaved Korean pine forest in northeastern China. Functional diversity was calculated from six plant traits, and aboveground biomass (AGB) and coarse woody productivity (CWP) were estimated using data from three forest censuses (10 years) in two large fully mapped forest plots (25 and 5 ha). 11 of the 12 regressions between biomass variables (AGB and CWP) and indices of diversity showed significant positive relationships, especially those with phylogenetic diversity. The mean tree diversity-biomass regressions increased from 0.11 in secondary forest to 0.31 in old-growth forest, implying a stronger biodiversity effect in more mature forest. Multi-model selection results showed that models including species richness, phylogenetic diversity, and single functional traits explained more variation in forest biomass than other candidate models. The models with a single functional trait, i. e., leaf area in secondary forest and wood density in mature forest, provided better explanations for forest biomass than models that combined all six functional traits. This finding may reflect different strategies in growth and resource acquisition in secondary and oldgrowth forests.

High tree species diversity in tropical forests is driven by reduced interspecific competition relative to intraspecific competition, as a result of the asynchronous timing of tree recruitment permitted by long and stable growing seasons. Forest diversity with latitude The number of tree species that coexist on a hectare scale rises by more than two orders of magnitude from boreal to tropical forests. Jacob Usinowicz and colleagues assess the extent to which latitudinal differences in competition between species shape this gradient, using seed production and seedling recruitment data from ten forests spanning the tropics to the boreal zone. They show that the longer and more stable growing seasons in the tropics permit greater differentiation between species in terms of the seasonal timing of reproduction. This asynchrony in the timing of tree recruitment reduces the degree of competition between species in the tropics, relative to forests at higher latitudes, thereby increasing the potential for species coexistence. The findings highlight the contribution that local-scale ecological processes can make to global-scale gradients in biodiversity. The tropical forests of Borneo and Amazonia may each contain more tree species diversity in half a square kilometre than do all the temperate forests of Europe, North America, and Asia combined 1 . Biologists have long been fascinated by this disparity, using it to investigate potential drivers of biodiversity 2 . Latitudinal variation in many of these drivers is expected to create geographic differences in ecological 2 , 3 , 4 and evolutionary processes 4 , 5 , and evidence increasingly shows that tropical ecosystems have higher rates of diversification, clade origination, and clade dispersal 5 , 6 . However, there is currently no evidence to link gradients in ecological processes within communities at a local scale directly to the geographic gradient in biodiversity. Here, we show geographic variation in the storage effect, an ecological mechanism that reduces the potential for competitive exclusion more strongly in the tropics than it does in temperate and boreal zones, decreasing the ratio of interspecific-to-intraspecific competition by 0.25% for each degree of latitude that an ecosystem is located closer to the Equator. Additionally, we find evidence that latitudinal variation in climate underpins these differences; longer growing seasons in the tropics reduce constraints on the seasonal timing of reproduction, permitting lower recruitment synchrony between species and thereby enhancing niche partitioning through the storage effect. Our results demonstrate that the strength of the storage effect, and therefore its impact on diversity within communities, varies latitudinally in association with climate. This finding highlights the importance of biotic interactions in shaping geographic diversity patterns, and emphasizes the need to understand the mechanisms underpinning ecological processes in greater detail than has previously been appreciated.

Interactions among neighbors influence the structure of communities of sessile organisms. Closely related species tend to share habitat and resource requirements and to interact with the same mutualists and natural enemies so that the strength of interspecific interactions tends to decrease with evolutionary divergence time. Nevertheless, the degree to which such phylogenetically related ecological interactions structure plant communities remains unclear. Using data from five large mapped forest plots combined with a DNA barcode mega-phylogeny, we employed an individual-based approach to assess the collective effects of focal tree size on neighborhood phylogenetic relatedness. Abundance-weighted average divergence time for all neighbors (ADT_all) and for heterospecific neighbors only (ADT_hetero) were calculated for each individual of canopy tree species. Within local neighborhoods, we found phylogenetic composition changed with focal tree size. Specifically, significant increases in ADT_all with focal tree size were evident at all sites. In contrast, there was no significant change in ADT_hetero with tree size in four of the five sites for both sapling-sized and all neighbors, even at the smallest neighbourhood scale (0–5 m), suggesting a limited role for phylogeny-dependent interactions. However, there were inverse relationships between focal tree size and the proportion of heterospecific neighbors belonging to closely related species at some sites, providing evidence for negative phylogenetic density dependence. Overall, our results indicate that negative interaction with conspecifics had a much greater impact on neighborhood assemblages than interactions among closely related species and could contribute to community structure and diversity maintenance in different forest communities.

1. Studying the spatial pattern of plants may provide significant insights into processes and mechanisms that maintain species richness. We used data from a fully mapped 25-ha temperate forest plot at Changbaishan (CBS), north-eastern China, to conduct a community-wide assessment of the type and frequency of intra- and interspecific spatial association patterns. We analysed complex scale effects in the patterning of large trees of 15 common species. First, we tested for overall spatial patterning at 6, 30 and 50 m neighbourhoods and classified the types of bivariate association patterns at these spatial scales (analysis 1). We then explored small-scale (0-20 m) association patterns conditioning on the larger-scale pattern (analysis 2) and tested for positive large-scale (50-250 m) association patterns (analysis 3). 2. Analysis 1 provided ample evidence for non-random spatial patterning, and the type and frequency of spatial association patterns changed with scale. Trees of most species pairs co-occurred less than expected by chance and positive associations were rare in local neighbourhoods. Analysis 2 revealed a separation of scales in which significant small-scale interactions faded away at distances of 10-15 m. One third of all species pairs showed significant and mostly negative bivariate small-scale association, which occurred more often than expected by chance between species sharing attributes such as family, fruit type and habitat association. This suggests the occurrence of competitive interactions. Analysis 3 showed that only 8% of all species pairs co-occurred at large scales. 3. Comparison of our results with an analogous study conducted in the species-rich tropical forest at Sinharaja, Sri Lanka, revealed several structural similarities including the dominance of segregation and partial overlap in the overall patterning (analysis 1) and the separation of scales (analysis 2). However, species pairs at CBS showed considerably more significant negative small-scale associations (31% vs. 6% at Sinharaja). 4. Synthesis. The techniques presented here allow for a detailed analysis of the complex spatial associations in species-rich forests and have the potential to reveal indicative patterns that may allow researchers to discriminate among competing hypotheses of community assemblage and dynamics. However, this will require comparative studies involving a large number of plots.