Yan Zhu

The mechanisms controlling plant growth are important to understand as they are key to forest carbon sequestration. Growth is species-specific and depends on mycorrhizal associations, resource availability, and neighbor competition. However, the difference in conspecific negative density dependence (CNDD) on growth between arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) species across life stages needs exploration. Using data from a 20 ha warm temperate deciduous broad-leaved forest in Donglingshan, China, we measured growth of established individuals. Using linear mixed-effects models, we assessed the combined effects of neighbor density, soil factors, and light availability on growth across life stages and mycorrhizal types. We observed reduced growth with increasing conspecific density, but effects varied between AM and EM species and between saplings and trees. Conspecific neighbor density had stronger negative effects on AM than EM saplings. For mature trees, conspecific density had weaker negative effects on AM species and no significant effect on EM species. Additionally, soil factors promoted AM sapling growth, while light promoted EM sapling growth. For trees, light promoted growth in both AM and EM species, whereas soil factors inhibited EM tree growth. Conspecific crowding, light and soil act jointly on growth, with CNDD strength set by mycorrhizal type and life stage.

The three-dimensional configuration of tree crowns controls resource distribution within canopies, thus driving forest ecosystem functioning, but landscape fragmentation and canopy structure degradation is causing forest biomass loss. Yet, how canopy structural diversity mediates the impact of anthropogenic disturbance on forest biomass remains poorly understood in urbanized regions, where population aggregates in cities and many of the rural areas were converted into built-up land. Here, we combined the Global Ecosystem Dynamics Investigation (GEDI) spaceborne LiDAR with Sentinel imagery to map forest aboveground biomass density (AGBD) at 30 m resolution across Beijing, China. We further assessed the relative contributions of canopy structural diversity (plant area index, PAI and canopy height diversity, H), anthropogenic disturbance (land surface temperature, LST and road network density, RND), and environmental factors (elevation and soil organic matter content, SOM) to AGBD using Bayesian regression modeling, and clarified the direct and indirect pathways linking them to AGBD by structural equation modeling. Results showed that (1) high biomass values were concentrated in mountainous forests, while fragmented lowland forests near urban infrastructure had substantially lower biomass; (2) human disturbance predominantly explained forest biomass variations (66%), followed by structural diversity (20%) and environmental factors (14%), while canopy structural diversity promoted biomass mostly through PAI; and (3) human disturbance (RND and LST) negatively affected biomass, both directly and indirectly by reducing PAI. Our findings highlight canopy structural diversity as a critical mediator between urban disturbance and forest biomass, and demonstrate the potential of GEDI-based monitoring to inform vegetation restoration and sustainable regional planning.

Trait‐based approaches are widely used to understand variation in plant demographic performance, yet their predictive power is often limited by context dependence. In particular, trait–demography relationships may shift across life stages and be modulated by local abiotic and biotic conditions. However, few studies have simultaneously examined how ontogeny, soil fertility, and neighborhood trait composition jointly shape the outcomes of trait–performance relationships. Here, we integrate long‐term demographic data, functional traits, and soil variables from a 20‐ha warm temperate forest dynamics plot to evaluate how three key traits, specific leaf area (SLA), leaf dry matter content (LDMC), and wood density (WD), affect tree growth and survival across seedling, sapling, and adult stages. We also examine how these effects, including neighborhood interactions for trait dissimilarity, are modified by soil fertility. Our study showed that soil fertility modulated trait effects on tree performance, which varied across life stages. Direct trait effects were detected primarily at the adult stage, where adult survival increased with WD but decreased with LDMC. In contrast, at the seedling and sapling stages, trait effects on survival were largely contingent on soil nutrients. Increasing soil organic matter, moisture, and available potassium intensified the negative effects of conservative traits (LDMC and WD) on seedling and sapling survival, while alleviating the negative effects of acquisitive traits (SLA). Seedlings exhibited lower survival when surrounded by heterospecific neighbors with dissimilar SLA. The negative effect of SLA dissimilarity among neighboring seedlings on seedling survival was amplified in soils rich in organic matter, moisture, and available potassium, whereas between seedlings and neighboring trees it was alleviated under higher nitrogen and phosphorus availability. Our results demonstrate the importance of explicitly considering life stage, local abiotic conditions, and biotic neighborhood context. This multidimensional approach offers new insights into trait‐based mechanisms underlying forest community dynamics across life stages.

The successful establishment of seedlings is shaped by a variety of biotic and abiotic factors. In particular, increasing density of conspecific neighbors often leads to decreases in seedling survival, a phenomenon referred to as conspecific negative density dependence (CNDD). Studies have found that the strength of CNDD often varies between tree species that associate with different mycorrhizal symbionts. In addition, CNDD strength can vary among sites that differ in abiotic conditions. Using data on seedlings (< 1 cm diameter at 1.3 m above ground; DBH) and trees (≥ 1 cm DBH) from the Donglingshan 20‐ha warm temperate forest dynamics plot (FDP) in Beijing, China, we tested whether the probability of a seedling surviving was related to the density of conspecific seedling and large (≥ 1 cm DBH) neighbors, and whether the strength of conspecific neighborhood effects differed between species associated arbuscular mycorrhizae (AM) versus ectomycorrhizae (EcM) or with soil nutrient availability. Contrary to our expectation, conspecific seedling neighborhood density was positively related to seedling survival, irrespective of species mycorrhizal type. The positive effect of conspecific seedling neighborhood density on seedling survival was stronger as soil nutrient availability increased. In contrast, seedling survival decreased with increasing conspecific large neighborhood density, and this effect was more negative for AM seedlings compared to EcM seedlings, while soil nutrient availability did not influence the effect of large neighbors on seedling survival. These findings illustrate the essential roles played by neighborhood interactions, mycorrhizal type, and abiotic factors in seedling survival. CNDD in seedling survival potentially contributes to understanding the maintenance of species diversity in this temperate forest, particularly for AM species. Understanding these processes that determine species diversity holds the key to improving forest conservation and management strategies in the context of biodiversity loss.

Herbaceous plants are an essential component of forest diversity and driver of ecosystem processes. However, because the growth forms and life-history strategies of herbaceous plants differ from those of woody plants, it is unclear whether the mechanisms that drive patterns plant diversity and community structure in these two plant groups are the same. In this study, we determined whether herb and woody plant communities have similar patterns and drivers of alpha- and beta-diversity. We compared species richness, distribution, and abundance of herbs to woody seedlings in a 20-ha Donglingshan warm-temperate forest (Donglingshan FDP), China. We also determined whether variation in patterns of species richness and composition are better explained by environmental or spatial variables. Herbaceous plants accounted for 72% of all species (81 herbaceous, 31 woody) recorded. Alpha- and beta-diversity were higher in herbs than in woody seedlings. Although alpha-diversity of herbs and woody seedlings was not correlated across the site, the local-site contributions to beta-diversity for herbs and woody seedlings were negatively correlated. Habitat type explained slightly more variation in herb community composition than in woody seedling composition, with the highest diversity in the low-elevation slope. Environmental variables explained the variation in species richness and composition more in herbaceous plants than in woody seedlings. Our results indicate that different mechanisms drive variation in the herb and woody seedling communities, with herbs exhibiting greater environmental sensitivity and habitat dependence. These findings contribute to the better understanding of herbaceous plant diversity and composition in forest communities.

To explore how traits determine demographic performance is an important goal of plant community ecology in explaining the assembly and dynamics of ecological communities. However, whether the prediction of individual-level trait data is more precise compared to species average trait data is questioned. Here, we analyzed the growth and trait data for 11 species collected from October 2018 to October 2020 in a temperate forest, Donglingshan, Beijing. To quantify the relationships between traits and growth rate, we conducted linear regression models at both the species and individual levels, as well as developed structural equation models at both levels. We found there was a clear difference in growth between the warm and cold seasons, with tree growth mainly concentrated in the warm season. Growth rate was positively correlated with the specific leaf area, while negatively correlated with leaf thickness and wood density without considering environmental information. Adding important contextual information in the analysis of species-level structural equation modeling, growth rates were positively correlated with specific leaf area and leaf thickness. However, in the individual-level, there was a negative correlation between growth rate and wood density. Our study showed that individual-level trait data have better predictions for individual growth than species-level data. When we use multiple traits and establish links between traits and tree size, we generated strong predictive relationships between traits and growth rates. Furthermore, our study highlighted that the importance of incorporating topographical factors and considering different seasons to assess the relationship between tree growth and functional traits.

Species richness and diversity substantially affect forest structures and function and are critical indicators of sustainable forest management. Sampling surveys are widely used in forest inventories because they efficiently assess forest characteristics. However, an appropriate sample plot design is required. The objectives of this study were to evaluate the effects of plot design on estimating species richness and species diversity using a simulation. A 20 ha census plot was established in a temperate forest to obtain the true values of species richness and species diversity. One single plot design and nine cluster plot designs were evaluated. The results indicated significant differences in forest species richness and species diversity for different plot designs. The cluster plot design with a square subplot configuration (SCONFIG) and extent of ground area covered by a cluster (EGROUND) of 500 m² exhibited the best performance (accuracy, precision) in estimating forest species richness. In contrast, a rectangular cluster plot with an EGROUND of 1000 m² was more suitable for assessing species diversity. This study demonstrates that cluster plots outperform a single plot for evaluating species richness and species diversity in temperate forests.

Subtropical natural forests are unique due to their ecological and economic functions. However, most of these forests are highly degraded, which impairs the ability to provide ecological and economic benefits. Enrichment planting is an important approach to restore natural degraded forests. Species arrangement is of great importance to inform enrichment planting. Species association refers to the interrelationship of different species occupying a habitat and is a static description of the organic connection formed by the interaction of species. Species association, therefore, provides a scientific basis for species arrangement in enrichment planting. Additionally, because an old-growth forest is a climax community that has attained great age without significant disturbance, the species association in an old-growth forest can provide valuable information on the reference conditions for forest management. In this study, the species association between dominant tree species (including saplings and adult trees) was investigated in an old-growth forest in the Gutianshan National Nature Reserve in Zhejiang province in subtropical China. The objective of the study was to inform species arrangement for enrichment planting. The result showed that the overall species association exhibited a significant net positive association, indicating a dynamic balance of stable structure and species composition in the old-growth forest. Additionally, the pairwise species association was examined using the χ² test, the Dice index, and Spearman’s rank correlation coefficient; significant positive and negative pairwise species associations were detected. Based on the species association and the light requirements of the tree species, an optimal species arrangement was determined to support enrichment planting for restoring natural degraded forests. It is expected that the results of this study will contribute to the restoration of natural degraded forests in subtropical China.

Species coexistence in diverse communities likely results from multiple interacting factors. Mechanisms such as conspecific negative density dependence (CNDD) and varying life‐history strategies related to resource partitioning are known to influence plant fitness, and thereby community composition and diversity. However, we have little understanding of how these mechanisms interact and how they vary across life stages. Here, we document the interaction between CNDD and life‐history strategy, based on growth‐mortality trade‐offs, from seedling to adult tree for 47 species in a tropical forest. Species’ life‐history strategies remained consistent across stages: fast‐growing species had higher mortality than slow‐growing species at all stages. In contrast, mean CNDD was strongest at early life stages (i.e. seedling, sapling). Fast‐growing species tended to suffer greater CNDD than slow‐growing species at several, but not all life stages. Overall, our results demonstrate that coexistence mechanisms interact across multiple life stages to shape diverse tree communities.