Diversity Of Forest Communities Research Articles

Forest community assembly is driven by different strata‐dependent mechanisms along an elevational gradient

AbstractAimThe mechanisms driving forest community assembly along elevational gradients remain elusive. The distinct strata in heterogeneous forest are subject to differing assembly mechanisms. This study aims to evaluate how different ecological mechanisms driving forest community assembly across strata and spatial scales, and to identify how these assemblages respond to different abiotic or biotic variables along an elevational gradient.LocationYulong Mountain within Hengduan Mountains, Southwest China.TaxonSeed plants.MethodsWe sampled plant species along a 1,200 m elevational gradient across forest strata (trees, shrubs and herbs) at different spatial scales (neighbourhood and community). We integrated phylogenetic and functional diversity to disentangle the roles of ecological mechanisms in structuring community assembly. We also determined the relative effects of climatic, soil and biotic variables and their interactions on these community assemblages.ResultsThe phylogenetic and functional diversity of trees were lower at the extremes of the elevational gradient, where they were constrained by water availability or temperature. While communities with higher species diversity exhibited an overdispersed structure at mid‐elevations. For shrubs, overdispersion was exhibited at high elevations despite low species richness, which could be consistent with facilitative interactions or competition exclusion. However, most communities of herbs appear to have a markedly random structure, despite some incongruence between phylogenetic divergence and functional convergence, as well as influences from overstorey trees and local light conditions. The relative effects of abiotic variables on community structure were larger at the community scale than at the neighbourhood scale.Main conclusionsOur study emphasises the importance of considering phylogenies and traits in understanding the strata‐ and scale‐dependent mechanisms of forest community assembly. Collectively, results indicate that contrasting assembly mechanisms interact across different strata along elevational gradients to shape diverse forest communities.

Acoustic monitoring reveals a diverse forest owl community, illustrating its potential for basic and applied ecology

Acoustic monitoring reveals a diverse forest owl community, illustrating its potential for basic and applied ecology

The use of DNA barcodes to estimate phylogenetic diversity in forest communities of southern China.

To elucidate potential ecological and evolutionary processes associated with the assembly of plant communities, there is now widespread use of estimates of phylogenetic diversity that are based on a variety of DNA barcode regions and phylogenetic construction methods. However, relatively few studies consider how estimates of phylogenetic diversity may be influenced by single DNA barcodes incorporated into a sequence matrix (conservative regions vs. hypervariable regions) and the use of a backbone family‐level phylogeny. Here, we use general linear mixed‐effects models to examine the influence of different combinations of core DNA barcodes (rbcL, matK, ITS, and ITS2) and phylogeny construction methods on a series of estimates of community phylogenetic diversity for two subtropical forest plots in Guangdong, southern China. We ask: (a) What are the relative influences of single DNA barcodes on estimates phylogenetic diversity metrics? and (b) What is the effect of using a backbone family‐level phylogeny to estimate topology‐based phylogenetic diversity metrics? The combination of more than one barcode (i.e., rbcL + matK + ITS) and the use of a backbone family‐level phylogeny provided the most parsimonious explanation of variation in estimates of phylogenetic diversity. The use of a backbone family‐level phylogeny showed a stronger effect on phylogenetic diversity metrics that are based on tree topology compared to those that are based on branch lengths. In addition, the variation in the estimates of phylogenetic diversity that was explained by the top‐rank models ranged from 0.1% to 31% and was dependent on the type of phylogenetic community structure metric. Our study underscores the importance of incorporating a multilocus DNA barcode and the use of a backbone family‐level phylogeny to infer phylogenetic diversity, where the type of DNA barcode employed and the phylogenetic construction method used can serve as a significant source of variation in estimates of phylogenetic community structure.

Disentangling the functional trait correlates of spatial aggregation in tropical forest trees.

Environmental filtering and dispersal limitation can both maintain diversity in plant communities by aggregating conspecifics, but parsing the contribution of each process has proven difficult empirically. Here, we assess the contribution of filtering and dispersal limitation to the spatial aggregation patterns of 456 tree species in a hyperdiverse Amazonian forest and find distinct functional trait correlates of interspecific variation in these processes. Spatial point process model analysis revealed that both mechanisms are important drivers of intraspecific aggregation for the majority of species. Leaf drought tolerance was correlated with species topographic distributions in this aseasonal rainforest, showing that future increases in drought severity could significantly impact community structure. In addition, seed mass was associated with the spatial scale and density of dispersal-related aggregation. Taken together, these results suggest environmental filtering and dispersal limitation act in concert to influence the spatial and functional structure of diverse forest communities.

Functional diversity research of forest communities in the Xiaowutai Mountain National Nature Reserve, Hebei

Plant functional traits are the plant physiological characteristics which can response to the changes of the living environment and have a certain impact on the ecosystem structure and function. The objective of our study was to explore characters of present functional diversity indices, the relationships between functional diversity and environmental variables, the relevance of species diversity and functional diversity. In this paper, habitat type, seed dispersal, pollination method, life cycle, life form, leaf form, leaf hair type, flowering period and flowering time were chosen as functional traits, and the research were done in the typical forest communities in the Xiaowutai Mountain National Nature Reserve, Hebei. One hundred and forty-eight quadrats (10m×10m) of forest communities were established along altitude gradients, at the same time, species composition, functional traits, and environmental variables were measured in each quadrat. The results showed that functional diversity indices in forest communities that were calculated by functional distances varied greatly. Functional diversity indices (FAD, MFAD, FDp, FDc, FRic, Rao and FDis) had highly significantly positive correlation with Patrick index and showed a linear increasing trend. All the nine functional diversity indices (FAD, MFAD, FDp, FDc, FRic, Rao, FEve, FDiv, FDis) had significantly correlation with Shannon-Wiener index and Pielou index. Only FDiv showed significantly negative correlation, and the other eight functional diversity indices showed positive correlation. Environmental filtering was important to functional diversity pattern, and functional diversity indices showed correlation with environmental variables. Altitude was a significant factor to functional diversity in forest communities. Except for FDiv, other functional diversity indices displayed a decreasing trend along altitude gradients. Among all the functional diversity indices, only Rao and FDis showed significantly positive correlation with aspect. The functional diversity indices (FAD, MFAD, FDp, FDc, FRic, Rao and FDdis) showed a negative correlation with slope, slope position, litter layer thickness, soil thickness, while, they showed a positive correlation with soil temperature and disturbance. All the nine indices were proved successful in the analysis of functional diversity in forest communities with different effectiveness. They were divided into three categories, functional richness (FAD, MFAD, FDp, FDc, FRic), functional divergence (Rao, FDis), functional evenness (FEve, FDis). Meanwhile, each category was highly inter-correlated and each category was relatively independent with other categories. The study of functional diversity provides a number of ecological indication and monitoring methods for the forest, and it can address a wide range of important ecological questions that links species and ecosystems through mechanisms in biodiversity research.

The roots of the drought: Hydrology and water uptake strategies mediate forest‐wide demographic response to precipitation

Abstract Drought‐induced tree mortality is expected to increase globally due to climate change, with profound implications for forest composition, function and global climate feedbacks. How drought is experienced by different species is thought to depend fundamentally on where they access water vertically below‐ground, but this remains untracked so far due to the difficulty of measuring water availability at depths at which plants access water (few to several tens of metres), the broad temporal scales at which droughts at those depths unfold (seasonal to decadal), and the difficulty in linking these patterns to forest‐wide species‐specific demographic responses. We address this problem through a new eco‐hydrological framework: we used a hydrological model to estimate below‐ground water availability by depth over a period of two decades that included a multi‐year drought. Given this water availability scenario and 20 year long‐records of species‐specific growth patterns, we inversely estimated the relative depths at which 12 common species in the forest accessed water via a model of water stress. Finally, we tested whether our estimates of species relative uptake depths predicted mortality in the multi‐year drought. The hydrological model revealed clear below‐ground niches as precipitation was decoupled from water availability by depth at multi‐annual scale. Species partitioned the hydrological niche by diverging in their uptake depths and so in the same forest stand, different species experienced very different drought patterns, resulting in clear differences in species‐specific growth. Finally, species relative water uptake depths predicted species mortality patterns after the multi‐year drought. Species that our method ranked as relying on deeper water were the ones that had suffered from greater mortality, as the zone from which they access water took longer to recharge after depletion. Synthesis. This research changes our understanding of how hydrological niches operate for trees, with a trade‐off between realized growth potential and survival under drought with decadal scale return time. The eco‐hydrological framework highlights the importance of species‐specific below‐ground strategies in predicting forest response to drought. Applying this framework more broadly may help us better understand species coexistence in diverse forest communities and improve mechanistic predictions of forests productivity and compositional change under future climate.

Maintaining ecosystem resilience: functional responses of tree cavity nesters to logging in temperate forests of the Americas

Logging often reduces taxonomic diversity in forest communities, but little is known about how this biodiversity loss affects the resilience of ecosystem functions. We examined how partial logging and clearcutting of temperate forests influenced functional diversity of birds that nest in tree cavities. We used point-counts in a before-after-control-impact design to examine the effects of logging on the value, range, and density of functional traits in bird communities in Canada (21 species) and Chile (16 species). Clearcutting, but not partial logging, reduced diversity in both systems. The effect was much more pronounced in Chile, where logging operations removed critical nesting resources (large decaying trees), than in Canada, where decaying aspen Populus tremuloides were retained on site. In Chile, logging was accompanied by declines in species richness, functional richness (amount of functional niche occupied by species), community-weighted body mass (average mass, weighted by species densities), and functional divergence (degree of maximization of divergence in occupied functional niche). In Canada, clearcutting did not affect species richness but nevertheless reduced functional richness and community-weighted body mass. Although some cavity-nesting birds can persist under intensive logging operations, their ecosystem functions may be severely compromised unless future nest trees can be retained on logged sites.

FUNCTIONAL DIVERSITY AND ITS ATTRIBUTE FACTORS IN THE YUNMENG MOUNTAIN NATIONAL FOREST PARK IN BEIJING, CHINA

ABSTRACT The interaction of diversity with environmental gradients is an important topic in ecology. This study investigated the pattern of change in functional diversity in forest communities along an altitudinal gradient in Yunmeng Mountain National Forest Park, China. Forty-two quadrats measuring 10 x 10 m in the forest communities were set up along this altitudinal gradient; plant species, traits and environmental variables were measured and recorded. Six functional diversity indices, namely, Modified functional attribute diversity (MFAD), Functional diversity plot-based dendrogram index (FDp), Functional diversity community-based dendrogram index (FDc), Functional evenness (FEve), Functional divergence (FDiv) and Functional dispersion (FDis), were used to calculate functional diversity. The results showed that functional diversity varied greatly in forest communities in the Yunmeng Mountain Forest Park. Functional diversity was significantly correlated with elevation and slope position and somewhat correlated with soil depth. Functional diversity increased with an increase in the elevation and decreased as the slope position changed from valley bottom to hill ridge. Functional diversity was closely related to species richness. The six functional diversity indices were all applicable to functional diversity studies of forest communities.

山西文峪河上中游森林群落多样性

PDF HTML阅读 XML下载 导出引用 引用提醒 山西文峪河上中游森林群落多样性 DOI: 10.5846/stxb201605090894 作者: 作者单位: 山西大学黄土高原研究所,山西大学黄土高原研究所,太原工业学院 环境与安全工程系,山西大学黄土高原研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 科技部科技基础性工作专项资助项目（2011FY110300，2015FY110300）；山西省自然科学基金资助项目（20130110371）；我国主要灌丛植物群落调查资助项目（2015FF110300）；2016年山西省研究生教育创新项目（2016BY015） Diversity of forest communities in the upstream and middle reaches of the Wenyu River watershed, Shanxi Author: Affiliation: Institute of the Loess Plateau,Shanxi University,Institute of the Loess Plateau,Shanxi University,Department of Environmental and Safety Engineering, Taiyuan Institute of Technology,Institute of the Loess Plateau,Shanxi University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于山西文峪河上中游森林群落的野外调查数据，选取植物生活型、生活史、固氮类型、传粉途径、种子传播途径等14个植物功能性状，计算丰富度指数（R）、多样性指数（H'）、均匀度指数（E）等物种多样性指数和功能丰富度指数（FRic）、功能均匀度指数（FEve）、功能分歧度指数（FDiv）等功能多样性指数，并用TWINSPAN对森林群落进行分类，Spearman秩相关分析多样性指数间及其与环境因子间的相关性，对山西文峪河上中游森林群落多样性进行研究。结果表明：青杄林种数最多（R=27），辽东栎油松林和油松林种数最少（R=16）；白桦林的H'和E最大，油松林的H'和E最小。山杨白桦林的FRic值最大，白杄林的FRic值最小；青杄林的FEve值最大，山杨白桦林的FEve值最小；山杨林的FDiv值最大，白桦林的FDiv值最小。文峪河上中游森林群落物种多样性指数与功能多样性指数间相关性不显著（P > 0.05），仅FDiv与H'呈显著负相关关系（P < 0.05）；物种多样性指数间呈极显著相关关系（P < 0.01），功能多样性指数间相关性不显著（P > 0.05），仅FRic与FEve呈显著负相关关系（P < 0.05）；随着海拔增加，物种多样性指数增加（P < 0.05或P < 0.01），但功能多样性指数减小（P < 0.01或P > 0.05）。 Abstract:Over the past 10 years, ecosystem functional diversity has played an important role in ecological research. Many studies have revealed that biodiversity has a substantial impact on ecosystem function through functional diversity, i.e., functional diversity is the factor closely related to the ecological process of biological diversity. The diversity of forest communities in the upstream and middle reach of the Wenyu River watershed, Shanxi was studied based on the field survey data. In the forest communities, we determined the growth form, life history, types of nitrogen fixation, C3/C4 type, light tolerance, leaf type, flower type, pollination mode, fruit type, seed propagation, flowering time, flowering phase, fruitage time and fruit season. These variables were used as plant functional traits to calculate species diversity indices, including richness index (R), species diversity index (H'), and evenness index (E), as well as functional diversity indices including the functional richness index (FRic), functional evenness index (FEve), and functional divergence degree index (FDiv). Classification of forest communities was analyzed using TWINSPAN and the correlation among diversity indices and between diversity indices and environmental factors were determined using Spearman's rank correlation analysis. The results indicated that:1) Based on the TWINSPAN classification results and in accordance with the principle and method of classification of vegetation, 52 forest quadrats in the upstream and middle reach of the Wenyu watershed were classified into nine formations, including Form. Betula platyphylla, Form. Picea meyeri, Form. Larix principis-ruprechtii, Form. Quercus wutaishanica, Form. Quercus wutaishanica+Pinus tabuliformis, Form. Picea wilsonii, Form. Populus davidiana+Betula platyphylla, Form. Populus davidiana and Form. Pinus tabuliformis. 2) The number of species was greatest in Form. Picea wilsonii (R=27) and Form. Quercus wutaishanica+Pinus tabuliformis, whereas Form. Pinus tabuliformis had the least (R=16); the H' and E of Form. Betula platyphylla were the largest, and they were smallest for Form. Pinus tabuliformis. 3) The FRic of Form. Populus davidiana+Betula platyphylla was largest, and it was smallest for Form. Picea meyeri; the FEve of Form. Picea wilsonii was the largest, and it was smallest for Form. Populus davidiana+ Betula platyphylla; the FDiv of Form. Populus davidiana was largest, and it was smallest for Form. Betula platyphylla. 4) There was no correlation between the forest community species diversity index and functional diversity index (P > 0.05), with only FDiv and H' being significantly negatively correlated (P < 0.05). 5) The correlation between the species diversity indices was highly significant (P < 0.01), the correlation between the functional diversity indices was not significant (P > 0.05), and FRic and FEve were significantly negatively correlated (P < 0.05). 6) The R value and altitude were highly significantly positively correlated (P < 0.01), the H' value and altitude were significantly positively correlated (P < 0.05), the H' the E values were significantly negatively correlated (P < 0.05), the FDiv value and latitude were highly significantly negatively correlated (P < 0.01), the FDiv value and altitude were highly significantly negatively correlated (P < 0.01). 7) As altitude increased, the species diversity index increased, and the linear relationship between the R and E values changed with altitude and was significant (P < 0.05); the linear relationship between the H' value and altitude was highly significant (P < 0.01), but as the functional diversity index decreased, the linear relationship between the FRic and FEve values changed with altitude was not significant (P > 0.05); the linear relationship between the FDiv value and altitude was highly significant (P < 0.01). 参考文献 相似文献 引证文献

Study on Diversity of Undergrowth Plant Community in Cibagou Nature Reserve

The forest community diversity along the altitudinal gradient was analyzed in the Cibagou National Nature Reserve. Results showed that the forest types of Cibagou Gorge could be divided into six types: Castanopsis hystrix forest; camphor and acer mixed forest, blue Japanese oak broad-leaved mixed forest, blue Japanese oak forest, Populus simonii mixed forest; Quercus aquifolioides forest. The total coverage of undergrowth vegetation altitude was the lowest at 1749 m, only 30%, and plant species numbers in the sample was only 5. The total coverage of the plant was the highest at 2327 m altitude, the value was 95%, and the number of species in experiment plot was 14. The species richness of Margalef increased first and then decreased with the increase of altitude gradient at 1749 m to 2880 m, and the Shannon-wiener species diversity index increased, but the difference was not significant, Pielou species evenness and Sheldon species evenness index decreased first and then increased with altitude.

Habitat and conservation status of molinillo (Magnolia sambuensis) and laurel arenillo (Magnolia katiorum), two endangered species from the lowland, Colombia

The conservation of the Magnoliaceae family is considered a priority worldwide, especially in Colombia, where all of its 36 species are seriously endangered while frustratingly little is known about their ecology. We therefore, assessed some ecological aspects of two lowland forest species: laurel arenillo ( Magnolia katiorum) and molinillo ( M. sambuensis). The first is an endemic species of the Urabá region in northwestern Colombia, and the second is distributed from Panama to Colombia along the Chocó Biogeographical region. Both species have a very low tree density and are found in forest stands that are disturbed by the timber exploitation of valuable woody species. The trees of both species had an average height of 26 m and shared similar environmental conditions such as soil (25°C) and air (28°C) temperatures, soil moisture (113%), and slope (25%). A redundancy analysis showed that each Magnolia species grows in a different community. Laurel arenillo was not a clear dominant species in a more diverse forest community, and was positively associated to altitude, longitudinal slope, and soil humidity. In contrast, molinillo was positively associated to air temperature and transversal slope and was negatively associated with longitudinal slope. This species was the most dominant in its community, which was less diverse than that of laurel arenillo. The last species should be considered a priority for conservation while the conservation status of molinillo should be further reviewed. Both species displayed large, fragrant, eye-catching flowers throughout most of the year.

Resilience of Amazon forests emerges from plant trait diversity

Application of a terrestrial biogeochemical model that simulates diverse forest communities suggests that plant trait diversity may enable the Amazon rainforest to adjust to new climate conditions via a process of ecological sorting.

Biodiversity investigation on forest communities in lantau, HongKong

Biodiversity investigation on forest community structures were conducted under different gradients of human disturbance in Lantau, Hong Kong. The results show that species diversity of forest community decreases along the disturbance gradient of different intensity, diversity of forest community of natural growing vegetation (hill) diversity of light disturbed (Ngong Ping) diversity of heavy disturbed (Tung Chung). The species compositions and dominance also vary with the intensity of human-induced disturbance. Exotic species are introduced into the communities purposedly by human activities, and therefore build up new community structures. The ecolgical impact of exotic species should be investigated from several respects in more details.

Local Seed Source Availability Limits Young Seedling Populations for Some Species More Than Other Factors in Northern Hardwood Forests

Light is generally regarded as the most important factor affecting tree regeneration in selection managed forests. For decades this paradigm guided forestry in the Great Lakes region, where small harvest gaps were used to promote shade-tolerant species. However, recent attempts to regenerate a more diverse forest community, by varying harvest gap size, have been less successful, bringing the predominance of light into question. Here, we investigate the influence of light availability along with local seed production potential [Σ(diameter2/distance2)] (SPP), substrate availability, site quality, and nontree vegetation (NTV) on 8 tree species' initial density and survival in 19 stands located throughout the Northern Lower and Eastern Upper Peninsula of Michigan. Larger-seeded, shade-tolerant to mid-tolerant sugar maple, red maple, and white ash seedlings were at least twice as abundant as those of any other species. Light availability was not a strong factor predicting seedling density, except for sugar maple, which showed a negative response to increasing light. In contrast, SPP had a strong positive influence on yellow birch, eastern hemlock, black cherry, and white ash seedling density, with evidence of local and regional seed source limitations. Substrate availability was an important factor influencing white pine and paper birch seedling density, as each species was significantly more abundant in plots dominated by bare mineral soil than in plots dominated by leaf litter. Collectively, these results suggest that from seed through two growing seasons, SPP and substrate availability can exert a stronger influence on seedling layer diversity than light availability created by harvest gaps.

Neighbourhood structure and light availability influence the variations in plant design of shrubs in two cloud forests of different successional status.

Plant design refers to the construction of the plant body or its constituent parts in terms of form and function. Although neighbourhood structure is recognized as a factor that limits plant survival and species coexistence, its relative importance in plant design is not well understood. We conducted field research to analyse how the surrounding environment of neighbourhood structure and related effects on light availability are associated with changes in plant design in two understorey plants (Palicourea padifolia and Psychotria elata) within two successional stages of a cloud forest in Costa Rica. Features of plant neighbourhood physical structure and light availability, estimated using hemispherical photographs, were used as variables that reflect the surrounding environment. Measures of plant biomechanics, allometry, branching and plant slenderness were used as functional plant attributes that reflect plant design. We propose a framework using a partial least squares path model and used it to test this association. The multidimensional response of plant design of these species suggests that decreases in the height-based factor of safety and increases in mechanical load and developmental stability are influenced by increases in maximum height of neighbours and a distance-dependence interference index more than neighbourhood plant density or neighbour aggregation. Changes in plant branching and slenderness are associated positively with light availability and negatively with canopy cover. Although it has been proposed that plant design varies according to plant density and light availability, we found that neighbour size and distance-dependence interference are associated with changes in biomechanics, allometry and branching, and they must be considered as key factors that contribute to the adaptation and coexistence of these plants in this highly diverse forest community.

Conspecific negative density dependence decreases with increasing species abundance

Conspecific negative density dependence (CNDD) is often involved in explaining the maintenance of species diversity in forest communities given that it may suppress the common species. Recent studies, in contrast, suggested that CNDD had a stronger effect on rare species than on common species and thus shaped the current tree abundance pattern. However, this finding was obtained mainly in the tropical forest and mixed results also occurred in the similar area. In addition, experimental test of the role of soil biota in maintaining this relationship is rare. In this study, two parallel manipulative shade‐house and field experiments were conducted in a subtropical evergreen broad‐leaved forest to test whether abundant species showed weaker CNDD than rarer species and whether susceptibility to soil biota was sufficient to maintain this relationship. The shade‐house experiment provided strong evidence for negative density‐dependent effects, and the strength of the density effect was significantly decreased along with the increase of the tree abundance. In the field experiment, a similar result was obtained. The density effect did not correlate with tree abundance after the sterilized treatment in the shade‐house experiment and the fungicide treatment in the field. Our results indicated that CNDD was negatively corrected with tree abundance in this subtropical forest and that soil biota played an important role in maintaining the relationship.

Choosing species for reforestation in diverse forest communities: social preference versus ecological suitability

Choosing species for reforestation programs or community forestry in species‐rich tropical rainforest ecosystems is a complex task. Reforestation objectives, social preferences, and ecological attributes must be balanced to achieve landscape restoration, timber production, or community forestry objectives. Here we develop a method to make better species choices for reforestation programs with native species when limited silvicultural information is available. We conducted community surveys to determine social preference of tree species and inferred their ecological suitability for open‐field plantations from growth rates and frequency in forest plots at different successional stages. Several species, for which silvicultural data was available, were correctly classified as promising or unsuitable for open‐field reforestation. Notably, we found a strong negative correlation between ecological suitability indicators and socioeconomic preference ranks. Only a single outlier species ranked very high in both categories. This result highlights the difficulty of finding suitable native species for community forestry and offers an explanation why reforestation efforts with native species often fail. We concluded that the approach should be a useful first screening of species‐rich forest communities for potential reforestation species. Our results also support the view that species‐rich tropical rainforests are not an easily renewable natural resource in a sense that secondary forests will not provide an equivalent resource value to local communities.

Drivers of bacterial beta diversity in two temperate forests

AbstractAlthough the consequences of changes in microbial diversity have received increasing attention, our understanding of processes that drive spatial variation in microbial diversity remains limited. In this study, we sampled bacterial communities in early and late successional temperate forests in Northeast China, and used distance‐based redundancy analysis to examine how different processes influence bacterial beta diversity and phylogeny‐based beta diversity using the Bray–Curtis and UniFrac metrics, respectively. After controlling for sampling effects, bacterial beta diversity in both forests was higher than expected by chance, which indicates that the bacterial community showed strong intraspecific aggregation. Both environmental filtering and dispersal limitation contributed to bacterial beta diversity and phylogeny‐based beta diversity in the two forests. However, the relative importance of these different processes varied between the two forests. In the early successional forest, dispersal limitation played a dominant role in structuring the bacterial community, whereas the effects of environmental filtering were more important in the late successional forest. Our study revealed that bacterial beta diversity and phylogeny‐based beta diversity in forest communities from the same region are regulated by different forces and that the relative importance of different forces varies over succession.

Ontogenetic shifts in trait-mediated mechanisms of plant community assembly.

Identifying the processes that maintain highly diverse plant communities remains a central goal in ecology. Species variation in growth and survival rates across ontogeny, represented by tree size classes and life history stage-specific niche partitioning, are potentially important mechanisms for promoting forest diversity. However, the role of ontogeny in mediating competitive dynamics and promoting functional diversity is not well understood, particular in high-diversity systems such as tropical forests. The interaction between interspecific functional trait variation and ontogenetic shifts in competitive dynamics may yield insights into the ecophysiological mechanisms promoting community diversity. We investigated how functional trait (seed size, maximum height, SLA, leaf N, and wood density) associations with growth, survival, and response to competing neighbors differ among seedlings and two size classes of trees in a subtropical rain forest in Puerto Rico. We used a hierarchical Bayes model of diameter growth and survival to infer trait relationships with ontogenetic change in competitive dynamics. Traits were more strongly associated with average growth and survival than with neighborhood interactions, and were highly consistent across ontogeny for most traits. The associations between trait values and tree responses to crowding by neighbors showed significant shifts as trees grew. Large trees exhibited greater growth as the difference in species trait values among neighbors increased, suggesting trait-associated niche partitioning was important for the largest size class. Our results identify potential axes of niche partitioning and performance-equalizing functional trade-offs across ontogeny, promoting species coexistence in this diverse forest community.

Variation in ectomycorrhizal fungal communities associated with Oreomunnea mexicana (Juglandaceae) in a Neotropical montane forest.

Neotropical montane forests are often dominated by ectomycorrhizal (EM) tree species, yet the diversity of their EM fungal communities remains poorly explored. In lower montane forests in western Panama, the EM tree species Oreomunnea mexicana (Juglandaceae) forms locally dense populations in forest otherwise characterized by trees that form arbuscular mycorrhizal (AM) associations. The objective of this study was to compare the composition of EM fungal communities associated with Oreomunnea adults, saplings, and seedlings across sites differing in soil fertility and the amount and seasonality of rainfall. Analysis of fungal nrITS DNA (nuclear ribosomal internal transcribed spacers) revealed 115 EM fungi taxa from 234 EM root tips collected from adults, saplings, and seedlings in four sites. EM fungal communities were equally species-rich and diverse across Oreomunnea developmental stages and sites, regardless of soil conditions or rainfall patterns. However, ordination analysis revealed high compositional turnover between low and high fertility/rainfall sites located ca. 6km apart. The EM fungal community was dominated by Russula (ca. 36 taxa). Cortinarius, represented by 14 species and previously reported to extract nitrogen from organic sources under low nitrogen availability, was found only in low fertility/high rainfall sites. Phylogenetic diversity analyses of Russula revealed greater evolutionary distance among taxa found on sites with contrasting fertility and rainfall than was expected by chance, suggesting that environmental differences among sites may be important in structuring EM fungal communities. More research is needed to evaluate whether EM fungal taxa associated with Oreomunnea form mycorrhizal networks that might account for local dominance of this tree species in otherwise diverse forest communities.