Low functional redundancy revealed high vulnerability of the subtropical evergreen broadleaved forests to environmental change

Anthropogenic-induced environmental changes threaten forest ecosystems by reducing their biodiversity and adaptive capacity. Understanding the sensitivity of ecosystem function to loss of diversity is vital in designing conservation strategies and maintaining the resilience of forest ecosystems in a changing world. Here, based on unique combinations of ten functional traits (termed as functional entities; FEs), we quantified the metrics of functional redundancy (FR) and functional vulnerability (FV) in 250 forest plots across five locations in subtropical evergreen broadleaved forests. We then examined the potential impacts of species loss on functional diversity in subtropical forest communities along environmental gradients (climate and soil). Results showed that the subtropical forests displayed a low level of functional redundancy (FR < 2). Over 75 % of the FEs in these subtropical forest communities were composed of only one species, with rare species emerging as pivotal contributors to these vulnerable FEs. The number of FEs and functional redundancy both increased with the rise in species richness, but functional vulnerability decreased with increasing species richness. Climatic factors, especially mean diurnal range, played crucial roles in determining the functions that the forest ecosystem delivers. Under variable temperature conditions, species in each plot were packed into a few FEs, leading to higher functional redundancy and lower functional vulnerability. These results highlighted that rare species contribute significantly to ecosystem functions and the highly diverse subtropical forest communities could show more insurance effects against species loss under stressful environmental conditions.

Assessing the functional vulnerability of woody plant communities within a large scale tropical rainforest dynamics plot

Introduction

Tropical forests are characterized by intricate mosaics of species-rich and structurally complex forest communities. Evaluating the functional vulnerability of distinct community patches is of significant importance in establishing conservation priorities within tropical forests. However, previous assessments of functional vulnerability in tropical forests have often focused solely on isolated factors or individual disturbance events, with limited consideration for a broad spectrum of disturbances and the responses of diverse species.

Methods

We assessed the functional vulnerability of woody plant communities in a 60-ha dynamic plot within a tropical montane rainforest by conducting in silico simulations of a wide range disturbances. These simulations combined plant functional traits and community properties, including the distribution of functional redundancy across the entire trait space, the distribution of abundance across species, and the relationship between species trait distinctiveness and species abundance. We also investigated the spatial distribution patterns of functional vulnerability and their scale effects, and employed a spatial autoregressive model to examine the relationships between both biotic and abiotic factors and functional vulnerability at different scales.

Results

The functional vulnerability of tropical montane rainforest woody plant communities was generally high (the functional vulnerability of observed communities was very close to that of the most vulnerable virtual community, with a value of 72.41% on average at the 20m×20m quadrat scale), and they exhibited significant spatial heterogeneity. Functional vulnerability decreased with increasing spatial scale and the influence of both biotic and abiotic factors on functional vulnerability was regulated by spatial scale, with soil properties playing a dominant role.

Discussion

Our study provides new specific insights into the comprehensive assessment of functional vulnerability in the tropical rainforest. We highlighted that functional vulnerabilities of woody plant communities and their sensitivity to environmental factors varied significantly within and across spatial scales in the tropical rainforest landscape. Preserving and maintaining the functionality of tropical ecosystems should take into consideration the variations in functional vulnerability among different plant communities and their sensitivity to environmental factors.

Latitudinal variation and driving factors of above-ground carbon proportion of large trees in old-growth forests across China

Large trees play a vital role in forest carbon stocks, dominating the distribution of community biomass. However, climate change and deforestation are reducing large trees globally, resulting in regional differences in their contribution to carbon stocks. Here, we examined the latitudinal change pattern and drivers of large trees' contributions to stand carbon stocks. Above-ground carbon storage was calculated for 530 plots in old-growth forests across China. Linear regression was used to calculate latitudinal variation in the proportion of above-ground carbon in large trees (i.e., AGC proportion). Variance partitioning and multiple linear regression were used to calculate the relative importance of species diversity, stand structure, functional traits, and environmental factors to AGC proportion. The study found that AGC proportion decreased with increasing latitude, averaging at 64.44 %. Stand structure, particularly the coefficient of variation of DBH, was identified as the key drivers of the AGC proportion. The number of common species (Hill's 1D) had no direct effect on the AGC proportion, while wood density, maximum tree height, and leaf nitrogen-to‑phosphorus ratio showed negative effects. The mass-ratio effects on AGC proportion were stronger than diversity effects. Climate variables primarily affected the AGC proportion through stand variables. These results indicate that simultaneously managing high diversity and AGC proportion may pose challenges. Moreover, considering the substantial contribution of large trees to carbon stocks, their storage capacity and sensitivity to environmental changes exert significant control over forest carbon cycles. Therefore, preserving and enhancing the carbon sink function of old-growth forests in the face of climate change and disturbance may depend primarily on protecting existing large trees and soon-to-be large-diameter trees.

Corrigendum: Identifying hotspots of woody plant diversity and their relevance with home ranges of the critically endangered gibbon (Nomascus hainanus) across forest landscapes within a tropical nature reserve

[This corrects the article DOI: 10.3389/fpls.2023.1283037.].

Compositional changes at neighborhood and stand scales during recovery of a tropical lowland rainforest after shifting cultivation on Hainan Island, China

Understanding compositional changes during secondary forest recovery is crucial for effective restoration efforts. While previous research has predominantly focused on shifts in species composition at the stand scale, this study delves into the recovery dynamics in three compositional aspects of location (neighbor distances), size (tree diameters), and species (tree species) at both stand and neighborhood scale. The investigation spans nine chronosequence plots within a tropical lowland rainforest ecosystem after shifting cultivation, including three each for young-secondary forests (18-30 years), old-secondary forests (60 years), and old-growth forests (without obvious human interference). The quantification of location, size, and species composition involved categorized neighbor distances (Near, Moderate, Far-distance), tree diameters (Small, Medium, Large-tree), and tree species (Pioneer, Intermediate, Climax-species) into three groups, respectively. Compositional changes at the stand scale (plot) were directly based on these groups, while at the neighborhood scale, assessment involved combination types of these groups within a neighborhood (comprising three adjacent trees). At the stand scale, neighbor distances shifted from Near to Moderate and Far, tree diameters transitioned from Small to Medium and Large, and tree species of Pioneer gave way to Climax. Meanwhile, at the neighborhood scale, there was a notable decline in the aggregations of Near-distance (N), Small-tree (S), and Pioneer-species (P), while the mixtures of Far and Moderate-distance (F-M), Large and Small-tree (L-S), and Climax and Intermediate-species (C-I) experienced a marked increase. The compositional change exhibited a recovery pattern, with the fastest recovery in neighbor distances, followed by tree diameters and tree species. Moreover, compositional recovery in tree diameters and tree species at the neighborhood scale generally lagged behind that at the stand scale. The study suggests that rapid restoration of secondary forest can be achieved by different targeted cutting according to the recovery stages, aimed at reduce the Pioneer-species, Small-tree and Near-distance in neighborhood. Our findings underscore that analyzing the compositional changes in three aspects at two scales not only provides a profound understanding of secondary forest recovery dynamics, but also offers valuable insights for guiding practices in the restoration of degraded forest ecosystems.

Consistent patterns of common species across tropical tree communities

Trees structure the Earth's most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1-6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth's 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world's most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.

Differences in functional niche hypervolume among four types of forest vegetation and their environmental determinants across various climatic regions in China

Functional traits play an important role in studying the functional niche in plant communities. However, it remains unclear whether the functional niches of typical forest plant communities in different climatic regions based on functional traits are consistent. Here, we present data for 215 woody species, encompassing 11 functional traits related to three fundamental niche dimensions (leaf economy, mechanical support, and reproductive phenology). These data were collected from forests across four climatic zones in China (tropical, subtropical, warm-temperate, and cold-temperate) or sourced from the literature. We calculated the functional niche hypervolume, representing the range of changes in the multidimensional functional niche. This metric quantifies how many functional niche spaces are occupied by existing plants in the community. Subsequently, we analyzed differences in functional niche hypervolume and their associated environmental factors across different types of forest vegetation. The results indicate that the functional niche hypervolume and the degree of forest vegetation overlap decrease with increasing latitude (e.g., from tropical rainforest to cold temperate coniferous forest). The total explanatory power of both climate and soil factors on the variation in functional niche hypervolume was 50%, with climate factors exhibiting a higher explanatory power than soil factors. Functional niche hypervolume is positively correlated with climate factors (annual mean temperature and annual precipitation) and negatively correlated with soil factors (soil pH, soil organic matter content, soil total nitrogen content, and soil total phosphorus content). Among these factors, annual mean temperature, soil pH, and soil total nitrogen content most significantly affect the difference in functional niche hypervolume among forest vegetation. Our study emphasizes the significant variation in the functional niche hypervolume among typical forest vegetation in China.

Identifying hotspots of woody plant diversity and their relevance with home ranges of the critically endangered gibbon (Nomascus hainanus) across forest landscapes within a tropical nature reserve

Introduction

To achieve effective conservation objectives, it is crucial to map biodiversity patterns and hotspots while considering multiple influencing factors. However, focusing solely on biodiversity hotspots is inadequate for species conservation on a landscape scale. This emphasizes the importance of integrating hotspots with the home ranges of species to identify priority conservation areas.

Methods

Compiling the vegetation data with environmental and anthropogenic disturbance data collected from kilometer-grid plots in Bawangling Nature Reserve, Hainan, China, we analyzed the spatial distribution of plant diversity (species richness and Shannon-Wiener index), as well as the main drivers affecting these patterns. We also investigated the spatial distribution of hotspots using a threshold approach and compared them with the home ranges of the flagship species, Hainan gibbon (Nomascus hainanus).

Result

Climate and soil are predominant drivers shaping the spatial pattern of plant diversity in Bawangling Nature Reserve, surpassing the influence of anthropogenic disturbance and topographic factors. Both diversity indices exhibit a generally similar pattern with exceptions in surrounding areas of Futouling and Elongling. The hotspots identified by the Shannon-Wiener index showed a higher spatial overlap with the home ranges of Hainan gibbon compared to the species richness hotspots. The recently established Hainan gibbon Group E in 2019, located 8 km away from the original Futouling habitat, does not coincide with identified hotspots.

Discussion

Our findings indicate that the hotspots of plant diversity within the habitat of Hainan gibbon Group E are relatively limited, emphasizing the necessity of giving precedence to its conservation. Integrating hotspots with the home ranges of critically endangered species offers decision-makers valuable information to establish rational conservation networks in the context of changing environments, as well as a reference for habitat restoration of species.

Alpha and beta diversity jointly drive the aboveground biomass in temperate and tropical forests

Changes in biodiversity often affect ecosystem functioning. However, most previous biodiversity and ecosystem functioning (BEF) studies have generally been limited to very small spatial grains. Thus, knowledge regarding the biodiversity-ecosystem functioning relationships across spatial scales is lacking. Moreover, the multiscale nature of biodiversity, and specifically β diversity (i.e., spatial heterogeneity in species composition) was still largely missing in BEF studies. Here, using the vegetation and functional trait data collected from four 6-ha forest dynamics plots (FDPs) in temperate and tropical forests in China, we examine the scale-dependent relationships between tree diversity and the aboveground biomass (AGB), as well as the roles of species spatial heterogeneity in determining the AGB. In tropical forests, the effect of species richness on AGB decreased with spatial grains, while functional dominance played a stronger role at larger spatial grains. In temperate forests, positive relationship between diversity and AGB occurred at all spatial grains, especially on smaller scales. In both temperate and tropical forests, β diversity was positively correlated with AGB, but weaker than α diversity in determining AGB. Overall, complementarity and selection hypothesis play dominant role in determining AGB in temperate and tropical forests, respectively. The roles of these underlying mechanisms are more pronounced with increasing spatial scales. β diversity, a hitherto underexplored facet of biodiversity, is likely to increase ecosystem functions by species spatial turnover and should not be neglected in BEF explorations. Our findings have practical implications for forest management and demonstrate that biotic heterogeneity plays an important positive role in ecosystem functioning.

The turnover dynamics of woody plants in a tropical lowland rain forest during recovery following anthropogenic disturbances

An important indicator of forest dynamics is the forest community turnover rate, which was defined as the relative change in a variable of interest (e.g., basal area or stem abundance) to its maximum or total in the community over a certain period. Community turnover dynamics in part explain the community assembly process and give insights for understanding forest ecosystem functions. Here, we assessed how anthropogenic disturbances (shifting cultivation, clear cutting) affect turnover relative to old growth forests in a tropical lowland rainforest. Using two censuses over 5 years of twelve 1-ha forest dynamics plots (FDPs), we compared turnover dynamics of woody plant, then analyzed the influencing factors. We found that community turnover dynamics of FDPs that experienced shifting cultivation were significantly higher than those experienced clear cutting or no disturbance, but little difference between clear cutting and no disturbance. Stem mortality and relative growth rates were the highest contributors to stem and basal area turnover dynamics of woody plants, respectively. Both stem and turnover dynamics of woody plants were more consistent by the dynamics of trees (DBH≥5 cm). Canopy openness, as the most important drivers, was positively correlated with turnover rates, while soil available potassium and elevation were negatively correlated with turnover rates. We highlight the long-term impacts of major anthropogenic disturbances on tropical natural forests. Different conservation and restoration strategies should be adopted for tropical natural forests experienced different disturbance types.

Assessing the recovery in species, size and location diversities of a lowland tropical rainforest after shifting cultivation by multiple indices at stand and neighborhood scales

Tropical forests are rapidly being converted for agricultural use, but abandoned agricultural lands can recover naturally through secondary succession. However, comprehensive knowledges of how species composition, size structure and spatial patterning (represented by species, size and location diversities) change during recovery at multiple scales are still lacking. Our aim was to explore these change patterns to understand the underlying mechanisms of forest recovery and propose corresponding solutions for restoring regrowing secondary forests. Here, twelve 1ha forest dynamics plots (4 plots each in young-secondary forests (YS), old-secondary forests (OS) and old-growth forests (OG) from a chronosequence of tropical lowland rainforest after shifting cultivation) were used to assessed the recovery in species, size and location diversity of trees at stand (plot) and neighborhood (focal tree and its neighbors) scale by using 8 indices. The relative recoveries of YS and OS were quantified by dividing each of the indices in YS and OS to those in OG. Results showed that species and size diversity increased while location diversity decreased with the recovery process. The relative recovery of location diversity was higher than those of species and size diversity in both YS and OS, while species diversity was only higher than size diversity in YS. The relative recovery of species diversity at neighborhood scale was higher than that at stand scale in OS, while there were no differences between scales in size and location diversity. Additionally, using only the Shannon index and Gini coefficient at two scales can provide consistent insights into the recovery patterns of diversity as indicated by the 8 indices. Our study demonstrated that recovery rates of secondary forests relative to old-growth counterparts could be comprehensively quantified using multiple diversity indices in three types at two scales. This quantitative assessment on the relative recovery of disturbed forests could be helpful in applying appropriate management activities and selecting rational approaches to speed up restoration process of degraded forest ecosystems.

Evenness of soil organic carbon chemical components changes with tree species richness, composition and functional diversity across forests in China

Higher tree species richness generally increases the storage of soil organic carbon (SOC). However, less attention is paid to the influence of varied tree species composition on SOC storage. Recently, the perspectives for the stronger persistence of SOC caused by the higher molecular diversity of organic compounds were proposed. Therefore, the influences of tree species richness and composition on the molecular diversity of SOC need to be explored. In this study, an index of the evenness of diverse SOC chemical components was proposed to represent the potential resistance of SOC to decomposition under disturbances. Six natural forest types were selected encompassing a diversity gradient, ranging from cold temperate to tropical forests. We examined the correlations of tree species richness, composition, and functional diversity, with the evenness of SOC chemical components at a molecular level by ¹³ C nuclear magnetic resonance. Across the range, tree species richness correlated to the evenness of SOC chemical components through tree species composition. The negative correlation of evenness of SOC chemical components with tree species composition, and the positive correlation of evenness of SOC chemical components with tree functional diversity were found. These indicate the larger difference in tree species composition and the lower community functional diversity resulted in the higher heterogeneity of SOC chemical components among the communities. The positive correlation of the evenness of SOC chemical components with the important value of indicator tree species, further revealed the specific tree species contributing to the higher evenness of SOC chemical components in each forest type. Soil fungal and bacterial α-diversity had effect on the evenness of SOC chemical components. These findings suggest that the indicator tree species conservation might be preferrable to simply increasing tree species richness, for enhancing the potential resistance of SOC to decomposition.

Conservation of rare and endangered plant species in China

Rare and endangered plant species (REPs) are facing high danger of extinction, yet a comprehensive and up-to-date review on their conservation in China is still lacking. This paper systematically collected studies and achievements on REPs conservation, including species surveys and monitoring, cause of endangerment, in situ conservation, ex situ conservation, reintroduction, propagation, conservation legislation, public participation, progress in conservation of wild plant with extremely small populations, and progress in China's implementation of the Convention on Biological Diversity. Although enormous advances have been made in conservation policies and legislations, protection systems, and research, as well as public education and international collaborations, the conservation efficiency is still restricted largely by the conflict between economic growth and biodiversity conservation in China. In order to meet its commitments to the new Post-2020 Global Biodiversity Framework, more work on basic investigation and long-term observation, as well as advanced technologies and application-oriented research on REPs should be carried out.

Species Diversity Regulates Ecological Strategy Spectra of Forest Vegetation Across Different Climatic Zones

Ecological strategy is the tactics employed by species in adapting to abiotic and biotic conditions. The ecological strategy spectrum is defined as the relative proportion of species in different ecological strategy types within a community. Determinants of ecological strategy spectrum of plant community explored by most previous studies are about abiotic factors. Yet, the roles of biotic factors in driving variations of ecological strategy spectra of forest communities across different geographic regions remains unknown. In this study, we established 200 0.04-ha forest dynamics plots (FDPs) and measured three-leaf functional traits of tree and shrub species in four forest vegetation types across four climatic zones. Based on Grime's competitor, stress-tolerator, ruderal (CSR) triangular framework, and the StrateFy method, we categorized species into four ecological strategy groups (i.e., C-, S-, Int-, and R-groups) and related the ecological spectra of the forests to three species diversity indices [i.e., species richness, Shannon-Wiener index, and stem density (stem abundance)]. Linear regression, redundancy analysis, and variance partition analysis were utilized for assessing the roles of species diversity in regulating ecological strategy spectra of forest communities across different climatic zones. We found that the proportion of species in the C- and Int-groups increased, while the proportion of species in the S-group decreased, with the increase of three indices of species diversity. Among the three species diversity indices, stem abundance played the most important role in driving variations in ecological strategy spectra of forests across different climatic zones. Our finding highlights the necessity of accounting for biotic factors, especially stem abundance, in modeling or predicting the geographical distributions of plant species with varied ecological adaptation strategies to future environmental changes.

Rare and common species contribute disproportionately to the functional variation within tropical forests

Understanding how functional traits and functional entities (FEs, i.e., unique combinations of functional traits) are distributed within plant communities can contribute to the understanding of vegetation properties and changes in species composition. We utilized investigation data on woody plants (including trees, shrubs and lianas) from 17 1-ha plots across six old-growth tropical forest types on Hainan island, China. Plant species were categorized as common (>1 individuals/ha) and rare species (≤1 individuals/ha) according to their abundance to determine how they contributed to different ecosystem functions. First, we assessed the differences in traits between common and rare species, and second, we examined functional redundancy, functional over-redundancy, and functional vulnerability for common and rare species of the forests. We found that both common species and rare species in each of the forest types were placed into just a few FEs, leading to functional over-redundancy and resulting in functional vulnerability. Rare species tended to have different trait values than those of common species, and were differently distributed among FEs, indicating different contributions to ecosystem functioning. Our results highlighted the disproportionate contribution of rare species in all of the studied forests. Rare species are more likely than common species to possess unique FEs, and thus, they have a disproportionately large contribution to community trait space. The loss of such species may impact the functioning, redundancy, and resilience of tropical forests.

Variation Patterns of Functional Trait Moments Along Geographical Gradients and Their Environmental Determinants in the Subtropical Evergreen Broadleaved Forests

Understanding how environmental change alters the composition of plant assemblages is a major challenge in the face of global climate change. Researches accounting for site-specific trait values within forest communities help bridge plant economics theory and functional biogeography to better evaluate and predict relationships between environment and ecosystem functioning. Here, by measuring six functional traits (specific leaf area, leaf dry matter content, leaf nitrogen, and phosphorus concentration, leaf nitrogen/phosphorus, wood density) for 292 woody plant species (48,680 individuals) from 250 established permanent forest dynamics plots in five locations across the subtropical evergreen broadleaved forests (SEBLF) in China, we quantified functional compositions of communities by calculating four trait moments, i.e., community-weighted mean, variance, skewness, and kurtosis. The geographical (latitudinal, longitudinal, and elevational) patterns of functional trait moments and their environmental drivers were examined. Results showed that functional trait moments shifted significantly along the geographical gradients, and trait moments varied in different ways across different gradients. Plants generally showed coordinated trait shifts toward more conservative growth strategies (lower specific leaf area, leaf N and P concentration while higher leaf nitrogen/phosphorus and wood density) along increasing latitude and longitude. However, trends opposite to the latitudinal and longitudinal patterns appeared in trait mean values along elevation. The three sets of environmental variables (climate, soil and topography) explained 35.0-69.0%, 21.0-56.0%, 14.0-31.0%, and 16.0-30.0% of the variations in mean, variance, skewness, and kurtosis across the six functional traits, respectively. Patterns of shifts in functional trait moments along geographical gradients in the subtropical region were mainly determined by the joint effects of climatic and edaphic conditions. Climate regimes, especially climate variability, were the strongest driving force, followed by soil nutrients, while topography played the least role. Moreover, the relationship of variance, skewness and kurtosis with climate and their geographical patterns suggested that rare phenotypes at edges of trait space were selected in harsher environments. Our study suggested that environmental filtering (especially climate variability) was the dominant process of functional assembly for forest communities in the subtropical region along geographical gradients.

Shifts in ecological strategy spectra of typical forest vegetation types across four climatic zones

Ecological strategy spectrum is the relative proportion of species in different categories of ecological strategies in a biotic community. Here, we explored ecological strategy spectra in typical forest vegetation types across four climatic zones in China. We classified ecological strategy categories by using the "StrateFy" ordination method based on three leaf functional traits. Results showed that the predominant ecological strategies of species in the tropical rainforest were CS-selected, and the predominant categories in the evergreen-deciduous broadleaved mixed forest and warm-temperate coniferous-broadleaved mixed forest were CSR and S/CSR categories respectively, whereas those in the cold-temperate coniferous forest were the S-selected ones. Ecological strategy richness of forest vegetation decreased significantly with the increase of latitude. The categories of ecological strategies with more component S increased while those with more component C decreased with the change of typical forest vegetation types from tropical rainforest through evergreen-deciduous broadleaved mixed forest and warm-temperate coniferous-broadleaved mixed forest to cool-temperate coniferous forest. Our findings highlight the usefulness of Grime's C-S-R scheme for predicting the responses of vegetation to environmental changes, and the results are helpful in further elucidating species coexistence and community assembly in varied climatic and geographic settings.

Disentangling Environmental Effects on the Tree Species Abundance Distribution and Richness in a Subtropical Forest

As a transitional vegetation type between evergreen broadleaved forest and deciduous broadleaved forest, evergreen-deciduous broadleaved mixed forest is composed of diverse plant species. This distinctive forest is generally distributed in mountainous areas with complex landforms and heterogeneous microenvironments. However, little is known about the roles of environmental conditions in driving the species diversity patterns of this forest. Here, based on a 15-ha plot in central China, we aimed to understand how and to what extent topographical characteristics and soil nutrients regulate the number and relative abundance of tree species in this forest. We measured environmental factors (terrain convexity, slope, soil total nitrogen, and phosphorus concentrations) and species diversity (species abundance distribution and species richness) in 20 m × 20 m subplots. Species abundance distribution was characterized by skewness, Berger-Parker index, and the proportion of singletons. The generalized additive model was used to examine the variations in diversity patterns caused by environmental factors. The structural equation model was used to assess whether and how topographical characteristics regulate species diversity via soil nutrients. We found that soil nutrients had significant negative effects on species richness and positive effects on all metrics of species abundance distribution. Convexity had significant positive effects on species richness and negative effects on all metrics of species abundance distribution, but these effects were mostly mediated by soil nutrients. Slope had significant negative effects on skewness and the Berger-Parker index, and these effects were almost independent of soil nutrients. Soil nutrients and topographical characteristics together accounted for 9.5-17.1% of variations in diversity patterns and, respectively, accounted for 8.9-13.9% and 3.3-10.7% of the variations. We concluded that soil nutrients were more important than topographical factors in regulating species diversity. Increased soil nutrient concentration led to decreased taxonomic diversity and increased species dominance and rarity. Convexity could be a better proxy for soil nutrients than slope. Moreover, these abiotic factors played limited roles in regulating diversity patterns, and it is possible that the observed patterns are also driven by some biotic and abiotic factors not considered here.

The Effects of Multi-Scale Climate Variability on Biodiversity Patterns of Chinese Evergreen Broad-Leaved Woody Plants: Growth Form Matters

Large-scale patterns of species diversity are thought to be linked to contemporary climate variability and Quaternary glacial–interglacial climate change. For plants, growth forms integrate traits related to competition or migration capacity, which determine their abilities to deal with the climate variability they face. Evergreen broad-leaved woody plants (EBWPs) are major components of numerous biomes in the subtropical and tropical regions. Hence, incorporating phylogenetic (temporal) and biogeographic (spatial) approaches, we assessed the relative importance of short- and long-term climate variability for biodiversity patterns of different growth forms (i.e., tree, shrub, liana, and bamboo) in EBWPs. We used a dated phylogeny and the distribution records for 6,265 EBWP species which are naturally occurred in China, and computed the corrected weighted endemism, standardized phylogenetic diversity and net relatedness index for the four growth forms, respectively. Ordinary least squares linear regressions, spatial error simultaneous autoregressive models, partial regression and hierarchical variation partitioning were employed to estimate the explanatory power of contemporary climate variability and climate-change velocity from the Last Glacial Maximum to the present. Our results showed that short- and long-term climate variability play complementary role in the biogeographic patterns of Chinese EBWPs. The former had larger effects, but the legacy effects of past climate changes were also remarkable. There were also differences in the effects of historical and current climate among the four growth forms, which support growth forms as a critical plant trait in predicting vegetation response to climate change. Compared to the glacial-interglacial climate fluctuation, seasonality as a unique feature of mid-latitude monsoon climate played a dominant role in the diversification and distribution of EBWP species at the macroscale. The results indicated that the relative importance of climate variability at different temporal scales may relate to distinct mechanisms. To understand effects of future climate change on species distribution more thoroughly, climate conditions in different time scales should be incorporated.

Effects of thinning on the demography and functional community structure of a secondary tropical lowland rain forest

Tropical secondary forests play a prominent role in conserving biodiversity and providing ecosystem services, but their recovery can be slow and their succession trajectory is distinct from old-growth forests. Thinning is an essential silvicultural approach to enhance the recovery rate and timber production of forests. However, the selection of trees to thin has been mainly based on size class rather than on species identity. There is little empirical or experimental evidence of species-focused thinning with the goal of altering species composition. We examined the effects of thinning on community structure, demographic rates, species richness and functional diversity of woody plants in a detailed investigation of 60-year-old secondary tropical lowland rain forest on Hainan Island, South China. The density and basal area of trees ≥5 cm DBH (diameter at breast height) increased significantly after five years' recovery with no significant change for saplings (DBH < 5 cm). Species composition after thinning changed significantly and mid-to late-successional species of both saplings and trees were more abundant after five years' recovery. The relative growth rates (RGR) and recruitment rates were significantly higher in thinning plots for both saplings and trees, and RGRs increased by 127% and 48%, respectively. The mortality rate decreased by 13% for trees and increased by 47% for saplings in thinning plots compared to the control. The community weighted mean (CWM) of the specific leaf area (SLA) of saplings showed a significantly decreasing trend while CWMs of wood density (WD) and mean maximum height (Hmax) of saplings increased after thinning. By contrast, CWMs of SLA and Hmax of trees were significantly higher, but WD was significantly lower- in thinning plots than the control. RGR and recruitment rate of saplings and trees increased significantly as thinning intensity increased. However, the thinning intensity had a weak or nil effect on the mortality rate. Our results support the selective removal and girdling of pioneer and mid-successional species in a way that could accelerate recovery and improve the growth and recruitment of late-successional species in tropical secondary forests. Thinning at a relatively low intensity can maintain species diversity and alter species functional composition. This outcome shows promise for improved future management of tropical forests in human-modified tropical forest landscapes.

Floristic composition and plant diversity in distribution areas of native species congeneric with Betula halophila in Xinjiang, northwest China

Betula halophila, a wild plant with extremely small populations, is endemic to Xinjiang, northwest China. Its wild populations have declined severely in the field. Understanding the patterns of floristic composition where congeneric species of B. halophila are distributed and their determinants is a necessary step to restore the wild populations. Based on literature records, specimen information, shared public data and field survey data, the patterns of floristic composition, diversity and environmental conditions of seed flora within the distribution areas of five native species (i.e. B. tianschanica, B. microphylla, B. pendula, B. rotundifolia and B. humilis), congeneric with B. halophila, were examined. The results are as follows. (1) There were 3013 species, 693 genera and 108 families of seed plants in the distribution area of these congeneric species of B. halophila, which accounted for 86.16%, 94.54% and 93.91% of the total seed plants in Xinjiang, respectively. (2) The family composition of seed flora in the distribution area of these congeneric species of B. halophila was mainly cosmopolitan; the genus composition of seed flora was dominated by temperate, mainly of northern temperate and Mediterranean components. (3) There are no significant differences existing in plant richness amongst the areas where each of the five congeneric species (B. tianshchanica, B. microphylla, B. pendula, B. rotundifolia and B. humilis) are distributed. (4) The influence of climate factors on species richness is significant across the whole distribution areas of the Betula genus, while the main environmental factors determining species richness are different amongst distribution areas of different species. Climate factors impacted significantly on species richness in distribution areas of tree species, but not in distribution areas of shrub species. This study provides a preliminary guideline for the conservation of B. halophila, a wild plant with extremely small populations in the field.

Plant Functional Niches in Forests Across Four Climatic Zones: Exploring the Periodic Table of Niches Based on Plant Functional Traits

Previous studies have indicated that a niche variation scheme, similar to the periodic table of elements, can be constructed based on functional traits. The periodic table of niches for species is defined as a multidimensional ordination scheme of niche relationships and their orders in a specific biotic community. Comparing functional trait-based niches is extremely useful in theoretical studies of plant ecological strategies, community assembly, and the geographic differentiation of biomes across different climatic zones. Here, data for 11 functional traits belonging to three fundamental niche dimensions (leaf economy, mechanical support, and reproductive phenology) were compiled for 215 woody species from forests across four climatic zones (tropical, subtropical, warm-temperate, and cold-temperate). We constructed the periodic table of niches based on the functional traits of plants in different communities and explored their variations among biomes. A principal component analysis (PCA) was performed to derive the dominant gradients of trait combinations for each individual niche dimensional dataset. Then species scores for the first two axes (PC1 and PC2) were used as inputs for a second PCA to ordinate species in the continuous niche space constrained by the three niche dimensions. Changes in the functional niches of plants from the four biomes along the PC1 and PC2 of niche space were examined based on species scores. Leaf economy was the dominant functional dimension in the plant niche space, followed by mechanical support. Considerable niche convergences among different species were found in the niche space for each biome, except cold-temperate forest. The species niches varied mainly with the increasing specific leaf area/decreasing stem tissue density along PC1, and with the decrease of leaf area/plant size along PC2 from tropical to temperate forests, suggesting that the ecological strategies of plants in the four biomes changed from conservative to acquisitive with an increase in latitude. Our results confirmed that the periodic table of niches does exist and can be constructed by major functional dimensions composed of dominant functional traits. The periodic table of niches effectively reflects the changes of ecological strategies of plant species in biomes across different climatic zones.

Plant functional traits regulate soil bacterial diversity across temperate deserts

Despite the known influence of plant diversity on soil microbial diversity, the potential role of plant functional traits in regulating soil bacterial diversity remains largely unclear. There is a lack of strong empirical evidence for the relative effects of plant diversity and functional traits on soil bacterial diversity across large-scale deserts. Here, we simultaneously explore the internal links among plant diversity, functional traits and soil bacterial diversity across 90 temperate deserts habitat of China, after accounting for confounding abiotic and spatial factors. The results showed that soil bacterial alpha and beta diversities were mainly determined by abiotic and spatial factors, follow by plant factors. However, plant diversity and functional traits played diverse roles in shaping soil bacterial alpha and beta diversities. Plant diversity exerted a substantial influence on soil bacterial beta diversity, but not on alpha diversity. In contrast, plant functional traits still directly influenced soil bacterial alpha and beta diversity, after accounting for other confounding key drivers. More precisely, plant functional traits surpass plant diversity in affecting soil bacterial alpha diversity. These results provide robust evidence that plant functional traits can effectively regulate soil bacterial diversity across temperate deserts. Taken together, we highlight the importance and irreplaceability of plant functional traits in predicting soil biodiversity under current and future global environmental changes.

Intraspecific trait variation and neighborhood competition drive community dynamics in an old-growth spruce forest in northwest China

Identifying the factors driving the growth and mortality of trees is important for understanding the mechanisms of forest dynamics. Here, we studied the growth and survival of trees ≥10 cm diameter at breast height (DBH) in a 15-ha temperate coniferous old growth forest plot in northwest China. We examined the relative importance of abiotic (i.e., soil nutrient and topographic) and biotic variables (i.e., tree size, competition intensity, and wood density of each individual) on the growth and mortality Picea schrenkiana, the dominant species in this forest. We found a high mortality rate and a low recruitment rate for P. schrenkiana over a period of six years. The total abundance and basal area of this species decreased, respectively. Overall, nearly 10% of P. schrenkiana individuals died. Our models of mortality had relatively low explanatory power (3% for all trees and 5% for trees <30 cm DBH), while growth models had moderate explanatory power. The growth of P. schrenkiana trees more strongly correlated with biotic factors (i.e., competition and trait) than abiotic factors (i.e., soil nutrients and topography). Overall, DBH, neighborhood crowding index (NCI), wood density (WD), and convexity explained 26% of the variation in the relative growth rate (RGR) of P. schrenkiana trees. The majority of this variation was explained by DBH alone. For trees with DBH <30 cm, DBH, NCI, WD, convexity, and slope) explained 29% of variation in RGR. In contrast, models of the absolute growth rate (AGR) of all P. schrenkiana trees only explained 3% of variation. For trees <30 cm DBH, NCI, WD, and slope explained 21% variation in AGR and the main part was explained by intraspecific variation in WD. Ultimately, our results highlight the importance of intraspecific variation in traits and competition when exploring demographic process in low-density and species-poor forests.

Plant Functional Traits Are the Mediators in Regulating Effects of Abiotic Site Conditions on Aboveground Carbon Stock-Evidence From a 30 ha Tropical Forest Plot

Understanding the relative contribution of abiotic and biotic factors to the formation of ecosystem functioning across scales is vital to evaluate ecosystem services. Here, we elucidate the effects of abiotic site conditions (i.e., soil and topographic properties) and plant functional traits on variations of stand aboveground carbon (AGC) stock in an old-growth tropical montane rain forest. The response-effect framework in functional ecology is adopted in examining how plant functional traits respond to environmental changes and affect ecosystem functioning. We measured specific leaf area and wood density of 270 woody plant species and estimated stand AGC stocks in a 30-ha forest plot. The relationships among environmental factors (ENVIRONMENT), community-weighted means of functional traits (TRAITS) and stand AGC stocks across nested spatial scales were disentangled by structural equation modeling. The results showed that the stands composed of 'acquisitive' species (high specific leaf area and low wood density) had low AGC, whereas stands composed of 'conservative' species (low specific leaf area and high wood density) had high AGC. TRAITS responded to ENVIRONMENT and affected AGC directly. ENVIRONMENT had an indirect effect on AGC through its direct effect on TRAITS. TRAITS were more important than ENVIRONMENT in driving variations of AGC. The effects of TRAITS on AGC increased, while the effects of ENVIRONMENT on AGC decreased with the increase of spatial scales in the tropical montane rain forest. Our study suggests that plant functional traits are the mediators in regulating effects of abiotic site conditions on ecosystem functions.

Diversity and distribution of food plants: Implications for conservation of the critically endangered Hainan gibbon

An understanding of the diversity and distribution patterns of Hainan gibbon (Nomascushainanus) foods is essential to its conservation. We used data from plots in various successional stages and Pinusmerkusii plantations (PF) of Bawangling National Nature Reserve (BNNR) to compare variations in food species diversity and composition amongst forest types. A total of 85 food species and 16,882 food plants individuals were found across forest types. Habitat-exclusive food species were most abundant in old growth natural forest (OGF), followed by mid-aged natural secondary forest (MSF). We did not find exclusive species in PF. For all food species, as well as each stem size class, PF displayed a lower species richness and abundance and, in addition, less similar species composition in each age class compared to secondary forests. The highest stem density and species richness were found in MSF. The abundance of food trees was higher in MSF and OGF than in young natural secondary forest. Results suggested that MSF could serve as an alternative habitat for Hainan gibbons after short-term recovery. Hainan gibbons might be limited to secondary forests older than 25 years old. PF was found to be unsuitable for Hainan gibbons.

Functional recovery of a subtropical evergreen-deciduous broadleaved mixed forest following clear cutting in central China

Ecosystem functioning is largely dependent on the functional traits of its component species. Most of the previous researches on ecosystem recovery have mainly focused on taxonomic composition but less attention is concentrated on functional community composition. Here, we examine the dynamic trend of functional community composition along a recovery chronosequence following clear cutting in subtropical evergreen-deciduous broadleaved mixed forest. Results showed that with the process of recovery, the functional composition changed from a community with high specific leaf area (CWM_ SLA), leaf nitrogen concentration (CWM_ LNC) and leaf phosphorus (CWM_ LPC) but low leaf thickness (CWM_ LT) and stem tissue density (CWM_ STD) to that with low CWM_ SLA, CWM_ LNC and CWM_ LPC but high CWM_ LT and CWM_ STD. Functional traits of evergreen and deciduous species were significantly different in each stage. Light availability and soil phosphorus were the most important influencing factors during the recovery. Our study suggests that the subtropical evergreen-deciduous broadleaved mixed forest is gradually shifting from a resource acquisitive to a resource conservative assemblage, in which evergreen species will become more and more dominant. Any management or conservation planning upon the forest ecosystem should integrate this dynamic trend of functional change.

Seed plant features, distribution patterns, diversity hotspots, and conservation gaps in Xinjiang, China

The flora in Xinjiang is unique. Decisions about biodiversity conservation and management based on seed plant diversity hotspots and conservation gaps in Xinjiang are essential to maintain this unique flora. Based on a species distribution dataset of seed plants, we measured seed plant diversity using species richness and phylogenetic diversity indices. Five percent of Xinjiang’s total land area with the highest biodiversity was used to identify hotspots for each index. In total, eight hotspots were identified. Most hotspots were located in mountainous areas, mainly in the Tianshan Mountains and Altai Mountains. Furthermore, we detected conservation gaps for Xinjiang’s seed flora hotspots by overlaying nature reserve maps on to maps of identified hotspots and we designated priority conservation gaps for hotspots by overlaying global biodiversity hotspot maps on to hotspot conservation gaps maps. Most of Xinjiang’s seed plant hotspots are poorly protected; only 10.45% of these hotspots were covered by nature reserves. We suggest that it is essential to promote network function of nature reserves within these hotspots in Xinjiang to conserve this unique flora.

Hotspot analyses indicate significant conservation gaps for evergreen broadleaved woody plants in China

Evergreen broadleaved woody plants (EBWPs) are dominant components in forests and savanna of the global tropic and subtropic regions. Southern China possesses the largest continuous area of subtropical EBWPs distribution, harboring a high proportion of endemic species. Hotspot and gap analyses are effective methods for analyzing the spatial pattern of biodiversity and conservation and were used here for EBWPs in China. Based on a distribution data set of 6,265 EBWPs with a spatial resolution of 50 × 50 km, we measured diversity of EBWPs in China using four indices: species richness, corrected weighted endemism, relative phylogenetic diversity, and phylogenetic endemism. According to the results based on 10% threshold, 15.73% of China’s land area was identified as hotspots using at least one diversity index. Only 2.14% of China’s land area was identified as hotspots for EBWPs by all four metrics simultaneously. Most of the hotspots locate in southern mountains. Moreover, we found substantial conservation gaps for Chinese EBWPs. Only 25.43% of the hotspots are covered by existing nature reserves by more than 10% of their area. We suggest to promote the establishment and management of nature reserve system within the hotspot gaps.

Fifth Ovarian Cancer Consensus Conference of the Gynecologic Cancer InterGroup: recurrent disease

This manuscript reports the consensus statements regarding recurrent ovarian cancer (ROC), reached at the fifth Ovarian Cancer Consensus Conference (OCCC), which was held in Tokyo, Japan, in November 2015. Three important questions were identified: (i) What are the subgroups for clinical trials in ROC? The historical definition of using platinum-free interval (PFI) to categorise patients as having platinum-sensitive/resistant disease was replaced by therapy-free interval (TFI). TFI can be broken down into TFIp (PFI), TFInp (non-PFI) and TFIb (biological agent-free interval). Additional criteria to consider include histology, BRCA mutation status, number/type of previous therapies, outcome of prior surgery and patient reported symptoms. (ii) What are the control arms for clinical trials in ROC? When platinum is considered the best option, the control arm should be a platinum-based therapy with or without an anti-angiogenic agent or a poly (ADP-ribose) polymerase (PARP) inhibitor. If platinum is not considered the best option, the control arm could include a non-platinum drug, either as single agent or in combination. (iii) What are the endpoints for clinical trials in ROC? Overall survival (OS) is the preferred endpoint for patient cohorts with an expected median OS < or = 12 months. Progression-free survival (PFS) is an alternative, and it is the preferred endpoint when the expected median OS is > 12 months. However, PFS alone should not be the only endpoint and must be supported by additional endpoints including pre-defined patient reported outcomes (PROs), time to second subsequent therapy (TSST), or time until definitive deterioration of quality of life (TUDD).

The impacts of selective logging and clear-cutting on woody plant diversity after 40years of natural recovery in a tropical montane rain forest, south China

Historically, clear-cutting and selective logging have been the commercial logging practices. However, the effect of these pervasive timber extraction methods on biodiversity in tropical forests is still poorly understood. In this study, we compared abiotic factors, species diversity, community composition, and structure between ca. 40-year-old clear-cut (MCC); ca. 40-year-old selectively logged (MSL); and tropical old growth montane rain forests (MOG) on Hainan Island, China. Results showed that there were a large number of trees with a diameter at breast height (DBH) <30cm in the two logged forests. Additionally, the two logged forests only had 40% of the basal area of the large trees (DBH≥30cm) found in the old growth forest. The species richness and Shannon-Wiener diversity indices generally showed no difference among the three forest types. MCC had 70% of the species richness of the large trees in the MOG, whereas MSL and MOG had similar species richness. High value timber species had similar species richness among the three forest types, but a lower abundance and basal area of large trees in MCC. The species composition was distinct between the three forests. Large trees belonging to the family Fagaceae dominated in the logged forests and played a more important role in the old growth forest. Huge trees (DBH≥70cm) were rare in MCC, but were frequently found in MSL. Most abiotic factors varied inconsistently among the three forest types and few variables related to species diversity, community structure and composition. Our study indicated that MSL had a relatively faster recovery rate than MCC in a tropical montane rain forest after 40years, but both logged forests had a high recovery potential over a long-term.

Microarray expression profiling of dysregulated long non-coding RNAs in Hirschsprung's disease reveals their potential role in molecular diagnosis

BACKGROUND

Hirschsprung's disease (HSCR) is one of the common digestive disorders in the new born. Long non-coding RNAs (lncRNAs) play an important role in various biological processes. However, knowledge on lncRNAs in HSCR is limited.

METHODS

The expression profile of lncRNAs in HSCR was obtained using microarray. A total of 2078 differentially expressed lncRNAs were detected by microarray in HSCR tissues compared with matched normal colon tissues (fold change ≥2, p < 0.05). Candidate biomarkers were selected from these differentially expressed lncRNAs based on artificial criterion (raw signal intensity ≥50; fold change ≥8) and then validated in 80 pairs of HSCR and normal tissues using quantitative real-time polymerase chain reaction (qRT-PCR). Moreover, the computational analysis was used to evaluate the lncRNA-microRNA and lncRNA-protein relationships.

KEY RESULTS

A panel of 5-lncRNAs was identified to distinguish HSCR from normal tissues with remarkable sensitivity and specificity. The area under the receiver operating characteristic curve (AUC) for HSCR identification in the validation set was 0.875. The bioinformatics analysis reveals that these dysregulated lncRNAs are mainly involved in RNA-protein relationships, including RNA splicing, binding, transport, processing, and localization.

CONCLUSIONS & INFERENCES

Our results are the first to report the expression profile of dysregulated lncRNAs in HSCR and infer that lncRNAs may serve as novel diagnostic biomarkers for HSCR.