Phylogenetic structure and phylogenetic diversity of angiosperm assemblages in forests along an elevational gradient in Changbaishan,China

Aims Understanding what drives the variation in species composition and diversity among local communities can provide insights into the mechanisms of community assembly. Because ecological traits are often thought to be phylogenetically conserved, there should be patterns in phylogenetic structure and phylogenetic diversity in local communities along ecological gradients. We investigate potential patterns in angiosperm assemblages along an elevational gradient with a steep ecological gradient in Changbaishan, China.Methods We used 13 angiosperm assemblages in forest plots (32×32 m) distributed along an elevational gradient from 720 to 1900 m above sea level. We used Faith's phylogenetic diversity metric to quantify the phylogenetic alpha diversity of each forest plot, used the net relatedness index to quantify the degree of phylogenetic relatedness among angiosperm species within each forest plot and used a phylogenetic dissimilarity index to quantify phylogenetic beta diversity among forest plots. We related the measures of phylogenetic structure and phylogenetic diversity to environmental (climatic and edaphic) factors.Important findings Our study showed that angiosperm assemblages tended to be more phylogenetically clustered at higher elevations in Changbaishan. This finding is consistent with the prediction of the phylogenetic niche conservatism hypothesis, which highlights the role of niche constraints in governing the phylogenetic structure of assemblages. Our study also showed that woody assemblages differ from herbaceous assemblages in several major aspects. First, phylogenetic clustering dominated in woody assemblages, whereas phylogenetic overdispersion dominated in herbaceous assemblages; second, patterns in phylogenetic relatedness along the elevational and temperature gradients of Changbaishan were stronger for woody assemblages than for herbaceous assemblages; third, environmental variables explained much more variations in phylogenetic relatedness, phylogenetic alpha diversity and phylogenetic beta diversity for woody assemblages than for herbaceous assemblages.     

Trait variation and functional diversity maintenance of understory herbaceous species coexisting along an elevational gradient in Yulong Mountain,Southwest China

Characterizing trait variation across different ecological scales in plant communities has been viewed as a way to gain insights into the mechanisms driving species coexistence. However, little is known about how changes in intraspecific and interspecific traits across sites influence species richness and community assembly, especially in understory herbaceous communities. Here we partitioned the variance of four functional traits (maximum height, leaf thickness, leaf area and specific leaf area) across four nested biological scales: individual, species, plot, and elevation to quantify the scale-dependent distributions of understory herbaceous trait variance. We also integrated the comparison of the trait variance ratios to null models to investigate the effects of different ecological processes on community assembly and functional diversity along a 1200-m elevational gradient in Yulong Mountain. We found interspecific trait variation was the main trait variation component for leaf traits, although intraspecific trait variation ranged from 10% to 28% of total variation. In particular, maximum height exhibited high plasticity, and intraspecific variation accounted for 44% of the total variation. Despite the fact that species composition varied across elevation and species richness decreased dramatically along the elevational gradient, there was little variance at our largest (elevation) scale in leaf traits and functional diversity remained constant along the elevational gradient, indicating that traits responded to smaller scale influences. External filtering was only observed at high elevations. However, strong internal filtering was detected along the entire elevational gradient in understory herbaceous communities, possibly due to competition. Our results provide evidence that species coexistence in understory herbaceous communities might be structured by differential niche-assembled processes. This approach--integrating different biological scales of trait variation--may provide a better understanding of the mechanisms involved in the structure of communities.     

Biodiversity patterns diverge along geographic temperature gradients

Models applying space-for-time substitution, including those projecting ecological responses to climate change, generally assume an elevational and latitudinal equivalence that is rarely tested. However, a mismatch may lead to different capacities for providing climatic refuge to dispersing species. We compiled community data on zooplankton, ectothermic animals that form the consumer basis of most aquatic food webs, from over 1200 mountain lakes and ponds across western North America to assess biodiversity along geographic temperature gradients spanning nearly 3750 m elevation and 30° latitude. Species richness, phylogenetic relationships, and functional diversity all showed contrasting responses across gradients, with richness metrics plateauing at low elevations but exhibiting intermediate latitudinal maxima. The nonmonotonic/hump-shaped diversity trends with latitude emerged from geographic interactions, including weaker latitudinal relationships at higher elevations (i.e. in alpine lakes) linked to different underlying drivers. Here, divergent patterns of phylogenetic and functional trait dispersion indicate shifting roles of environmental filters and limiting similarity in the assembly of communities with increasing elevation and latitude. We further tested whether gradients showed common responses to warmer temperatures and found that mean annual (but not seasonal) temperatures predicted elevational richness patterns but failed to capture consistent trends with latitude, meaning that predictions of how climate change will influence diversity also differ between gradients. Contrasting responses to elevation- and latitude-driven warming suggest different limits on climatic refugia and likely greater barriers to northward range expansion.     

Phylogenetic diversity of macromycetes and woody plants along an elevational gradient in Eastern Mexico

Phylogenetic information provides insight into the ecological and evolutionary processes that organize species assemblages. We compared patterns of phylogenetic diversity among macromycete and woody plant communities along a steep elevational gradient in eastern Mexico to better understand the evolutionary processes that structure their communities. Macrofungi and trees were counted and identified in eight sites from 100 to 3500 m asl, and sequence data retrieved from GenBank for the same or closely related species were used to reconstruct their phylogenies. Patterns of species richness and phylogenetic diversity were similar for both macrofungi and trees, but macromycete richness and diversity peaked at mid‐elevations, whereas woody plant richness and diversity did not show significant trends with elevation. Phylogenetic similarity among sites was low for both groups and decreased as elevational distance between sites increased. Macromycete communities displayed phylogenetic overdispersion at low elevations and phylogenetic clustering at high elevations; the latter is consistent with environmental filtering at high elevation sites. Woody plants generally exhibited phylogenetic clustering, consistent with the potential importance of environmental filtering throughout the elevational gradient.     

太白山森林样地系统发育多样性格局及其影响因素

太白山森林样地系统发育多样性格局及其影响因素 系统发育多样性指数常被用作区分植物群落构建过程中生态和演化过程的相对作用。系统发育多样性格局的推断方法(如系统树的构建和不同的系统发育多样性指数)、演化历史(如生活型)以及环境梯度都可能影响系统发育多样性格局的估计值,进而可能影响我们对植物群落构建过程的认知。因此,有必要区分这些因素如何作用于系统发育多样性格局的估计值,但其相对重要性及其交互作用仍不清楚。本研究利用位于太白山北坡沿海拔分布的20个森林样地(整体高差2800 m左右)的野外调查数据,包括274种木本植物和581种草本植物。对于上述样地内所有植物,我们构建了当前广泛采用的合成树和分子树以比较系统树的构建,特别是合成树末端的多歧分支结构,及其对系统发育多样性格局估计值的可能影响。同时,我们计算了每个样地的3种不同的系统发育多样性指数,包括Faith’s PD, 平均成对距离(MPD)和平均最近类群距离(MNTD),并分别对木本和草本植物进行计算。多模型比较分析系统发育多样性格局的估计值与系统树重建方法、多样性指数、生活型、海拔及其交互作用的最简约关系。研究结果表明,基于合成树和分子树所得到的系统发育多样性格局之间没有显著差异。海拔和多样性指数与生活型在解释系统发育多样性格局方面存在强烈的交互作用,并且能够解释44%以上的变异。系统发育多样性格局的估计值总体随海拔升高而降低,但草本植物相比木本植物变化更平缓。对于木本植物,3种系统发育多样性指数表现出一致的海拔分布格局(即系统发育聚集),而草本植物的平均成对距离指数则表现为随机的海拔分布格局。因此,分析沿环境梯度的系统发育多样性格局需要考虑系统发育格局的推断方法和演化历史的影响,以帮助我们更好地理解植物群落的构建过程。     

Phylogenetic alpha and beta diversities of butterfly communities correlate with climate in the western Swiss Alps

The observation of non‐random phylogenetic distribution of traits in communities provides evidence for niche‐based community assembly. Environment may influence the phylogenetic structure of communities because traits determining how species respond to prevailing conditions can be phylogenetically conserved. In this study, we investigate the variation of butterfly species richness and of phylogenetic α‐ and β‐diversities along temperature and plant species richness gradients. Our study indicates that butterfly richness is independently positively correlated to temperature and plant species richness in the study area. However, the variation of phylogenetic α‐ and β‐diversities is only correlated to temperature. The significant phylogenetic clustering at high elevation suggests that cold temperature filters butterfly lineages, leading to communities mostly composed of closely related species adapted to those climatic conditions. These results suggest that in colder and more severe conditions at high elevations deterministic processes and not purely stochastic events drive the assemblage of butterfly communities.     

A taxonomic,functional, and phylogenetic perspective on the community assembly of passerine birds along an elevational gradient in southwest China

Integrating multiple facets of biodiversity to describe spatial and temporal distribution patterns is one way of revealing the mechanisms driving community assembly. We assessed the species, functional, and phylogenetic composition and structure of passerine bird communities along an elevational gradient both in wintering and breeding seasons in the Ailao Mountains, southwest China, in order to identify the dominant ecological processes structuring the communities and how these processes change with elevation and season. Our research confirms that the highest taxonomic diversity, and distinct community composition, was found in the moist evergreen broadleaf forest at high elevation in both seasons. Environmental filtering was the dominant force at high elevations with relatively cold and wet climatic conditions, while the observed value of mean pairwise functional and phylogenetic distances of low elevation was constantly higher than expectation in two seasons, suggested interspecific competition could play the key role at low elevations, perhaps because of relative rich resource result from complex vegetation structure and human‐induced disturbance. Across all elevations, there was a trend of decreasing intensity of environmental filtering whereas increasing interspecific competition from wintering season to breeding season. This was likely due to the increased resource availability but reproduction‐associated competition in the summer months. In general, there is a clear justification for conservation efforts to protect entire elevational gradients in the Ailao Mountains, given the distinct taxonomic, functional, and phylogenetic compositions and also elevational migration pattern in passerine bird communities.     

Turnover of plant lineages shapes herbivore phylogenetic beta diversity along ecological gradients

Understanding drivers of biodiversity patterns is of prime importance in this era of severe environmental crisis. More diverse plant communities have been postulated to represent a larger functional trait‐space, more likely to sustain a diverse assembly of herbivore species. Here, we expand this hypothesis to integrate environmental, functional and phylogenetic variation of plant communities as factors explaining the diversity of lepidopteran assemblages along elevation gradients in the Swiss Western Alps. According to expectations, we found that the association between butterflies and their host plants is highly phylogenetically structured. Multiple regression analyses showed the combined effect of climate, functional traits and phylogenetic diversity in structuring butterfly communities. Furthermore, we provide the first evidence that plant phylogenetic beta diversity is the major driver explaining butterfly phylogenetic beta diversity. Along ecological gradients, the bottom up control of herbivore diversity is thus driven by phylogenetically structured turnover of plant traits as well as environmental variables.     

Plant functional and phylogenetic turnover correlate with climate and land use in the Western Swiss Alps

Aims Understanding the relative importance of historical and environmental processes in the structure and composition of communities is one of the longest quests in ecological research. Increasingly, researchers are relying on the functional and phylogenetic β-diversity of natural communities to provide concise explanations on the mechanistic basis of community assembly and the drivers of trait variation among species. The present study investigated how plant functional and phylogenetic β-diversity change along key environmental and spatial gradients in the Western Swiss Alps.Methods Using the quadratic diversity measure based on six functional traits—specific leaf area, leaf dry matter content, plant height, leaf carbon content, leaf nitrogen content and leaf carbon to nitrogen content alongside a species-resolved phylogenetic tree—we relate variations in climate, spatial geographic, land use and soil gradients to plant functional and phylogenetic turnover in mountain communities of the Western Swiss Alps.Important findings Our study highlights two main points. First, climate and land-use factors play an important role in mountain plant community turnover. Second, the overlap between plant functional and phylogenetic turnover along these gradients correlates with the low phylogenetic signal in traits, suggesting that in mountain landscapes, trait lability is likely an important factor in driving plant community assembly. Overall, we demonstrate the importance of climate and land-use factors in plant functional and phylogenetic community turnover and provide valuable complementary insights into understanding patterns of β-diversity along several ecological gradients.     

Disentangling the relative importance of species occurrence,abundance and intraspecific variability in community assembly: a trait‐based approach at the whole‐plant level in Mediterranean forests

Understanding which factors and rules govern the process of assembly in communities constitutes one of the main challenges of plant community ecology. The presence of certain functional strategies along broad environmental gradients can help to understand the patterns observed in community assembly and the filtering mechanisms that take place. We used a trait‐based approach, quantifying variations in aboveground (leaf and stem) and belowground (root) functional traits along environmental gradients in Mediterranean forest communities (south Spain). We proposed a new practical method to quantify the relative importance of species turnover (distinguishing between species occurrence and abundance) versus intraspecific variation, which allowed us to better understand the assemblage rules of these plant communities along environmental gradients. Our results showed that the functional structure of the studied plant communities was highly determined by soil environment. Results from our modelling approach based on maximum likelihood estimators showed a predominant influence of soil water storage on most of the community functional traits. We found that changes in community functional structure along environmental gradients were mainly promoted by species turnover rather than by intraspecific variability. Specifically, our new method of variance decomposition demonstrated that between‐site trait variation was the result of changes in species occurrence rather than in the abundance of certain dominant species. In conclusion, this study showed that water availability promoted the predominance of specific trait values (both in above and belowground fractions) associated to a resource acquisition or conservation strategy. In addition, we provided evidence that changes on community functional structure along the environmental gradient were mainly promoted by a process of species replacement, which represent a crucial step towards a more general understanding of the relative importance of intraspecific versus interspecific trait variation in these woody Mediterranean communities.     

Functional traits of tree species with phylogenetic signal co-vary with environmental niches in two large forest dynamics plots

Aims While using phylogenetic and functional approaches to test the mechanisms of community assembly, functional traits often act as the proxy of niches. However, there is little detailed knowledge regarding the correlation between functional traits of tree species and their niches in local communities. We suggest that the co-varying correlation between functional traits and niches should be the premise for using phylogenetic and functional approaches to test mechanisms of community assembly. Using functional traits, phylogenetic and environmental data, this study aims to answer the questions: (i) within local communities, do functional traits of co-occurring species co-vary with their environmental niches at the species level? and (ii) what is the key ecological process underlying community assembly in Xishuangbanna and Ailaoshan forest dynamic plots (FDPs)?Methods We measured seven functional traits of 229 and 36 common species in Xishuangbanna and Ailaoshan FDPs in tropical and subtropical China, respectively. We also quantified the environmental niches for these species based on conditional probability. We then analyzed the correlations between functional traits and environmental niches using phylogenetic independent contrasts. After examining phylogenetic signals of functional traits using Pagel's λ, we quantified the phylogenetic and functional dispersion along environmental gradients within local tree communities.Important findings For target species, functional traits do co-vary with environmental niches at the species level in both of the FDPs, supporting that functional traits can be used as a proxy for local-scale environmental niches. Functional traits show significant phylogenetic signals in both of the FDPs. We found that the phylogenetic and functional dispersion were significantly clustered along topographical gradients in the Ailaoshan FDP but overdispersion in the Xishuangbanna FDP. These patterns of phylogenetic and functional dispersion suggest that environmental filtering plays a key role in structuring local tree assemblages in Ailaoshan FDP, while competition exclusion plays a key role in Xishuangbanna FDP.     

Using phylogeny and functional traits for assessing community assembly along environmental gradients: A deterministic process driven by elevation

Community assembly processes is the primary focus of community ecology. Using phylogenetic‐based and functional trait‐based methods jointly to explore these processes along environmental gradients are useful ways to explain the change of assembly mechanisms under changing world. Our study combined these methods to test assembly processes in wide range gradients of elevation and other habitat environmental factors. We collected our data at 40 plots in Taibai Mountain, China, with more than 2,300 m altitude difference in study area and then measured traits and environmental factors. Variance partitioning was used to distinguish the main environment factors leading to phylogeny and traits change among 40 plots. Principal component analysis (PCA) was applied to colligate other environment factors. Community assembly patterns along environmental gradients based on phylogenetic and functional methods were studied for exploring assembly mechanisms. Phylogenetic signal was calculated for each community along environmental gradients in order to detect the variation of trait performance on phylogeny. Elevation showed a better explanatory power than other environment factors for phylogenetic and most traits’ variance. Phylogenetic and several functional structure clustered at high elevation while some conserved traits overdispersed. Convergent tendency which might be caused by filtering or competition along elevation was detected based on functional traits. Leaf dry matter content (LDMC) and leaf nitrogen content along PCA 1 axis showed conflicting patterns comparing to patterns showed on elevation. LDMC exhibited the strongest phylogenetic signal. Only the phylogenetic signal of maximum plant height showed explicable change along environmental gradients. Synthesis. Elevation is the best environment factors for predicting phylogeny and traits change. Plant's phylogenetic and some functional structures show environmental filtering in alpine region while it shows different assembly processes in middle‐ and low‐altitude region by different trait/phylogeny. The results highlight deterministic processes dominate community assembly in large‐scale environmental gradients. Performance of phylogeny and traits along gradients may be independent with each other. The novel method for calculating functional structure which we used in this study and the focus of phylogenetic signal change along gradients may provide more useful ways to detect community assembly mechanisms.     

The ecology of differences: assessing community assembly with trait and evolutionary distances

Species enter and persist in local communities because of their ecological fit to local conditions, and recently, ecologists have moved from measuring diversity as species richness and evenness, to using measures that reflect species ecological differences. There are two principal approaches for quantifying species ecological differences: functional (trait‐based) and phylogenetic pairwise distances between species. Both approaches have produced new ecological insights, yet at the same time methodological issues and assumptions limit them. Traits and phylogeny may provide different, and perhaps complementary, information about species' differences. To adequately test assembly hypotheses, a framework integrating the information provided by traits and phylogenies is required. We propose an intuitive measure for combining functional and phylogenetic pairwise distances, which provides a useful way to assess how functional and phylogenetic distances contribute to understanding patterns of community assembly. Here, we show that both traits and phylogeny inform community assembly patterns in alpine plant communities across an elevation gradient, because they represent complementary information. Differences in historical selection pressures have produced variation in the strength of the trait‐phylogeny correlation, and as such, integrating traits and phylogeny can enhance the ability to detect assembly patterns across habitats or environmental gradients.     

The influence of fire on phylogenetic and functional structure of woody savannas: Moving from species to individuals

Fire is a key determinant of tropical savanna structure and functioning. High fire frequencies are expected to assemble closely related species with a restricted range of functional trait values. Here we determined the effect of fire on phylogenetic and functional diversity of woody species and individuals in savanna communities under different fire frequencies. We found phylogenetic signals for one third of the functional traits studied. High numbers of fires simultaneously led to phylogenetic overdispersion and functional clustering when communities were represented by mean trait values with all traits that putatively should be affected or respond to fire. This finding is important, because it shows that the relationship between ecological processes and the phylogenetic structure of communities is not straightforward. Thus, we cannot always assume that close relatives are more similar in their ecological features. However, when considering a different set of traits representing different plant strategies (fire resistance/avoidance, physiological traits and regeneration traits), the results were not always congruent. When asking how communities are assembled in terms of individuals (not species) the outcome was different from the species-based approach, suggesting that the realised trait values – rather than mean species trait values – have an important role in driving community assembly. Thus, intraspecific trait variability should be taken into account if we want fully to improve our mechanistic understanding of assembly rules in plant communities.     

戴云山物种多样性与系统发育多样性海拔梯度分布格局及驱动因子

生物多样性的海拔分布格局是生态学研究的热点。海拔作为综合性因子驱动着植物群落的物种、系统发育与功能多样性的空间分布。以戴云山南坡900-1600 m森林植物群落为研究对象,探讨物种多样性、系统发育指数与环境驱动因子的相互关系以及环境因子在群落构建与多样性维持中的重要意义。结果表明：（1）森林植物群落的系统发育多样性与物种多样性沿海拔均呈现中间高度膨胀格局。（2）物种多样性Margalef指数、Shannon-Wiener指数与系统发育多样性指数呈显著正相关,表明物种多样性越高,系统发育多样性也越高。Shannon-Wiener指数与物种多样性指数（Margalef、Pielou、Simpson指数）、系统发育多样性及系统发育结构都存在显著相关性,一定程度上Shannon-Wiener指数可以代替其他指数。Pielou指数、Simpson指数、Shannon-Wiener指数与系统发育结构NRI （Net relatedness index）指数、NTI （Net nearest taxa index）指数存在显著正相关,表明群落优势度、均匀度与系统发育结构相关性较强。（3）土壤全磷含量是影响系统发育多样性和物种多样性的主要驱动因子,土壤含水量是影响Shannon-Wiener、Pielou、Simpson指数的最显著因子,海拔是影响群落系统发育结构的主要因素。海拔是影响系统发育结构变化的主要环境因子,而土壤因子是影响物种多样性与系统发育多样性的主要因素,进一步验证了物种多样性与系统发育多样性的高度相关,结果旨在揭示物种群落空间分布规律。     

Climatic correlates of phylogenetic relatedness of woody angiosperms in forest communities along a tropical elevational gradient in South America

Aims This study assesses the relationship between phylogenetic relatedness of angiosperm tree species and climatic variables in local forests distributed along a tropical elevational gradient in South America. In particular, this paper addresses two questions: Is phylogenetic relatedness of plant species in communities related to temperature variables more strongly than to water variables for tropical elevational gradients? Is phylogenetic relatedness of plant species in communities driven by extreme climatic conditions (e.g. minimum temperature (MT) and water deficit) more strongly than by climatic seasonal variability (e.g. temperature seasonality and precipitation seasonality)?Methods I used a set of 34 angiosperm woody plant assemblages along an elevational gradient in the Andes within less than 5 degrees of the equator. Phylogenetic relatedness was quantified as net relatedness index (NRI) and nearest taxon index (NTI) and was related to major climatic variables. Correlation analysis and structure equation modeling approach were used to assess the relationships between phylogenetic relatedness and climatic variables.Important findings Phylogenetic relatedness of angiosperm woody species in the local forest communities is more strongly associated with temperature-related variables than with water-related variables, is positively correlated with mean annual temperature (MAT) and MT, and is related with extreme cold temperature more strongly than with seasonal temperature variability. NTI was related with elevation, MAT and MT more strongly than was NRI. Niche convergence, rather than niche conservatism, has played a primary role in driving community assembly in local forests along the tropical elevational gradient examined. Negative correlations of phylogenetic relatedness with elevation and higher correlations of phylogenetic relatedness with elevation and temperature for NTI than for NRI indicate that evolution of cold tolerance at high elevations in tropical regions primarily occurred at recent (terminal) phylogenetic nodes widely distributed among major clades.     

Contrasting patterns of lichen functional diversity and species richness across an elevation gradient

Major environmental gradients co‐vary with elevation and have been a longstanding natural tool allowing ecologists to study global diversity patterns at smaller scales, and to make predictions about the consequences of climate change. These analyses have traditionally studied taxonomic diversity, but new functional diversity approaches may provide a deeper understanding of the ecological mechanisms driving species assembly. We examined lichen taxonomic and functional diversity patterns on 195 plots (200 m²) together with forest structure along an elevational gradient of 1000 m in a temperate low mountain range (Bohemian Forest, Germany). Along this elevation gradient temperature decreased and precipitation increased, two macroclimatic variables critical for lichens. Elevation was more important than forest structure in driving taxonomic and functional diversity. While species richness increased with elevation, functional diversity decreased and revealed that community patterns shift with elevation from random to clustered, reflecting selection for key shared traits. Higher elevations favored species with a complex growth form (which takes advantage of high moisture) and asexual reproductive mode (facilitating establishment under low temperature conditions). Our analysis highlights the need to examine alternative forms of diversity and opens the avenue for community predictions about climate change. For a regional scenario with increasing temperature and decreasing availability of moisture, we expect a loss of specialized species with a complex growth form and those with vegetative organs at higher elevations in low mountain ranges in Europe.     

Structure of herbaceous plant assemblages in a forested riparian landscape

We assessed patterns of herbaceous and woody species richness, plant-environment interactions, and correspondence between the herb and tree layer in a riparian landscape (the Ozark National Scenic Riverways, Missouri, USA). A total of 269 herb and 70 tree species were identified on 94 sample plots. Gradient analysis revealed that environmental variables and vegetation were influenced by a strong elevation gradient. However, high variability in environmental variables (pH, elevation, slope, sand, clay, organic matter) indicated a high level of substrate heterogeneity across the riparian landscape. We were unable to predict the composition of the herb understory from the canopy trees with any detailed accuracy and no clear characterization of herb species assemblages was found using cluster analysis or ecological land type (ELT) classifications. Canonical correspondence analysis (CCA) results for both tree and herb plots showed that elevation (height above river) and pH were the dominant environmental gradients influencing vegetation patterns on the first CCA axis while soil particle size exhibited the strongest correlation with the second CCA axis. Secondary gradients of importance included slope, soil container capacity, and organic matter. No significant linear or quadratic correlation was found between elevation and herb or woody species richness. Environmental variables alone or in combination, were weak predictors of herb and woody species richness, despite the patterns observed in the gradient analysis and the correlations observed in the CCA results. Ecotonal analysis showed that the herb layer exhibited a high species replacement rate at the lower elevations most susceptible to flooding (0–3 m). Above the flooding zone, there was more or less continuous species replacement, suggesting the presence of a gradual ecotone/ecocline. The tree layer exhibited much stronger discontinuities than the herb layer in the lower elevations along the height gradient (0–10 m). Recognizing the limitations of classification techniques for riparian herb assemblages and the importance of scale and heterogeneity in vegetation layers is especially important in light of mandates to preserve, protect, and manage for plant diversity.     

Does disturbance regime change community assembly of angiosperm plant communities in the boreal forest?

Aims To examine if and how species and phylogenetic diversity change in relation to disturbance, we conducted a review of ecological literature by testing the consistency of the relationship between phylogenetic diversity and disturbance and compared taxonomic groups, type of disturbance and ecosystem/habitat context. We provide a case study of the phylogenetic diversity–disturbance relationship in angiosperm plant communities of a boreal forest region, compared with types of natural and anthropogenic disturbances and plant growth forms.Methods Using a large-scale sampling plot network along a complete (0–100%) anthropogenic disturbance gradient in the boreal biome, we compared the changes of angiosperm plant community structure and composition across plots. We estimated natural disturbance with historical records of major fires. We then calculated phylogenetic diversity indexes and determined species richness in order to compare linear and polynomial trends along disturbance gradients. We also compared the changes of community structure for different types of anthropogenic disturbances and examined how the relationships between species and phylogenetic diversity and disturbance regimes vary among three different life forms (i.e. forbs, graminoids and woody plants).Important findings Phylogenetic diversity was inconsistently related to disturbance in previous studies, regardless of taxon, disturbance type or ecosystem context. In the understudied boreal ecosystem, angiosperm plant communities varied greatly in species richness and phylogenetic diversity along anthropogenic disturbance gradients and among different disturbance types. In general, a quadratic curve described the relationship between species richness and anthropogenic disturbance, with the highest richness at intermediate anthropogenic disturbance levels. However, phylogenetic diversity was not related to disturbance in any consistent manner and species richness was not correlated with phylogenetic diversity. Phylogenetic relatedness was also inconsistent across plant growth forms and different anthropogenic disturbance types. Unlike the inconsistent patterns observed for anthropogenic disturbance, community assembly among localities varying in time since natural disturbance exhibited a distinct signature of phylogenetic relatedness, although those trends varied among plant growth forms.