Trait-based Community Assembly Research Articles

Interacting ecological filters influence success and functional composition in restored plant communities over time.

A trait-based community assembly framework has great potential to direct ecological restoration, but uncertainty over how traits and environmental factors interact to influence community composition over time limits the widespread application of this approach. In this study, we examined how the composition of seed mixes and environment (north- vs. south-facing slope aspect) influence functional composition and native plant cover over time in restored grassland and shrubland communities. Variation in native cover over 4 years was primarily driven by species mix, slope aspect, and a species mix by year interaction rather than an interaction between species mix and slope aspect as predicted. Although native cover was higher on wetter, north-facing slopes for most of the study, south-facing slopes achieved a similar cover (65%-70%) by year 4. While community-weighted mean (CWM) values generally became more resource conservative over time, we found shifts in particular traits across community types and habitats. For example, CWM for specific leaf area increased over time in grassland mixes. Belowground, CWM for root mass fraction increased while CWM for specific root length decreased across all seed mixes. Multivariate functional dispersion remained high in shrub-containing mixes throughout the study, which could enhance invasion resistance and recovery following disturbance. Functional diversity and species richness were initially higher in drier, south-facing slopes compared to north-facing slopes, but these metrics were similar across north- and south-facing slopes by the end of the 4-year study. Our finding that different combinations of traits were favored in south- and north-facing slopes and over time demonstrates that trait-based approaches can be used to identify good restoration candidate species and, ultimately, enhance native plant cover across community types and microhabitat. Changing the composition of planting mixes based on traits could be a useful strategy for restoration practitioners to match species to specific environmental conditions and may be more informative than using seed mixes based on growth form, as species within functional groups can vary tremendously in leaf and root traits.

Phylogenetic and functional trait-based community assembly within Pacific Cyrtandra (Gesneriaceae): Evidence for clustering at multiple spatial scales.

Tropical rainforest communities are often characterized by a small number of species-rich genera that contribute disproportionately to the alpha diversity in these habitats. In the Pacific Basin, there are nearly 200 species of Cyrtandra, most of which are white-flowered woody shrubs that are single-island endemics. Within these island communities, multiple Cyrtandra species are commonly observed to occur sympatrically in wet forest understories, forming swarms of what appear to be ecologically similar taxa. The aim of this study was to determine whether species of these plants are randomly assembled with respect to phylogenetic relatedness and traits that are ecologically relevant. I examined assembly patterns across three Pacific archipelagoes using a combination of 10 functional traits and a well-resolved phylogeny comprising 34 species of Cyrtandra. Coexisting species were found to be more closely related and more phenotypically similar than would be expected by chance. This pattern was observed at both regional (island) and local (site) spatial scales. The retention of phylogenetic signal in floral traits and the strong influence of these traits on the observed degree of phylogenetic clustering may indicate that generalist insect pollinators act as a biotic filter on oceanic islands, driving selection for similar floral morphology among closely related species of Pacific Cyrtandra. Phylogenetic signal was also detected in leaf size, which contributed to niche clustering at both spatial scales. Coupled with a propensity for long-distance dispersal, and the restricted distribution of Cyrtandra to rainforest understories, this finding suggests that environmental filtering along this trait axis may be more important than dispersal limitation in determining species assemblages. This study supports the theory that plant species are not randomly assembled, and instead, that niche-based processes structure biodiversity at regional and local spatial scales in diverse congeneric species assemblages.

Inter- and intraspecific phytochemical variation correlate with epiphytic flower and leaf bacterial communities.

Microbes associated with flowers and leaves affect plant health and fitness and modify the chemical phenotypes of plants with consequences for interactions of plants with their environment. However, the drivers of bacterial communities colonizing above-ground parts of grassland plants in the field remain largely unknown. We therefore examined the relationships between phytochemistry and the epiphytic bacterial community composition of flowers and leaves ofRanunculus acris and Trifolium pratense. On 252 plant individuals, we characterized primary and specialized metabolites, that is, surface sugars, volatile organic compounds (VOCs), and metabolic fingerprints, as well as epiphytic flower and leaf bacterial communities. The genomic potential of bacterial colonizers concerning metabolic capacities was assessed using bacterial reference genomes. Phytochemical composition displayed pronounced variation within and between plant species and organs, which explained part of the variation in bacterial community composition. Correlation network analysis suggests strain-specific correlations with metabolites. Analysis of bacterial reference genomes revealed taxon-specific metabolic capabilities that corresponded with genes involved in glycolysis and adaptation to osmotic stress. Our results show relationships between phytochemistry and the flower and leaf bacterial microbiomes suggesting that plants provide chemical niches for distinct bacterial communities. In turn, bacteria may induce alterations in the plants' chemical phenotype. Thus, our study may stimulate further research on the mechanisms of trait-based community assembly in epiphytic bacteria.

Habitat configurations shape the trophic and energetic dynamics of reef fishes in a tropical–temperate transition zone: implications under a warming future

Understanding the extent to which species’ traits mediate patterns of community assembly is key to predict the effect of natural and anthropogenic disturbances on ecosystem functioning. Here, we apply a trait-based community assembly framework to understand how four different habitat configurations (kelp forests, Sargassum spp. beds, hard corals, and turfs) shape the trophic and energetic dynamics of reef fish assemblages in a tropical–temperate transition zone. Specifically, we tested (i) the degree of trait divergence and convergence in each habitat, (ii) which traits explained variation in species’ abundances, and (iii) differences in standing biomass (kg ha−1), secondary productivity (kg ha−1 day−1) and turnover (% day−1). Fish assemblages in coral and kelp habitats displayed greater evidence of trait convergence, while turf and Sargassum spp. habitats displayed a higher degree of trait divergence, a pattern that was mostly driven by traits related to resource use and thermal affinity. This filtering effect had an imprint on the trophic and energetic dynamics of reef fishes, with turf habitats supporting higher fish biomass and productivity. However, these gains were strongly dependent on trophic guild, with herbivores/detritivores disproportionately contributing to among-habitat differences. Despite these perceived overall gains, turnover was decoupled for fishes that act as conduit of energy to higher trophic levels (i.e. microinvertivores), with coral habitats displaying higher rates of fish biomass replenishment than turf despite their lower productivity. This has important implications for biodiversity conservation and fisheries management, questioning the long-term sustainability of ecological processes and fisheries yields in increasingly altered marine habitats.

Editorial: Trait-Based Plant Community Assembly, Ecological Restoration, and the Biocontrol of Invasive Exotic Plant Species

Editorial: Trait-Based Plant Community Assembly, Ecological Restoration, and the Biocontrol of Invasive Exotic Plant Species

Importance and benefit of incorporating the responses of species mean trait values in trait-based community assembly

Species mean trait values are the common currency of current trait-based community ecology, in which species are approximated by a set of constant mean trait values and are assumed to be passively selected by abiotic and biotic filters according to these values. However, species mean trait values can respond to both species interactions and the environmental context. Do such responses in traits subsequently alter the effect of filters on communities? Can we benefit by incorporating the responses of species mean trait values in trait-based community assembly? We tested the responses of mean values of four key functional traits to reduced light and interspecific competition in a two-year common garden experiment, using 1,584 seedlings of 11 tree species. We quantified the changes in interspecific trait differences, community-weighted means (CWM), and functional diversity (FD) and compared these to their corresponding changes under the assumption of constant mean trait values. Species mean values of most examined traits underwent substantial changes (mean = 18 ± 3%) to shading and interspecific competition treatments, but the direction and extent of these responses varied among traits and species, resulting in significant changes in interspecific trait differences, CWM and FD. Considering these trait responses largely improved our ability to identify these effects of low light and interspecific competition on CWM and FD. Further, we showed that strong abiotic filters could promote trait divergence if trait responses were considered, but that this pattern would be obscured if species mean trait values were considered as constant. Consequently, incorporating the responses of species mean trait values, e.g. using multiple mean values for a trait of a species in a heterogeneous environment, into the current trait-based community ecology offers us a more accurate, sensitive, and time-saving way to identify the underlying ecological mechanisms.

Chemical Similarity of Co-occurring Trees Decreases With Precipitation and Temperature in North American Forests

Plant diversity varies immensely over large-scale gradients in temperature, precipitation, and seasonality at global and regional scales. This relationship may be driven in part by climatic variation in the relative importance of abiotic and biotic interactions to the diversity and composition of plant communities. In particular, biotic interactions may become stronger and more host specific with increasing precipitation and temperature, resulting in greater plant species richness in wetter and warmer environments. This hypothesis predicts that the many defensive compounds found in plants’ metabolomes should increase in richness and decrease in interspecific similarity with precipitation, temperature, and plant diversity. To test this prediction, we compared patterns of chemical and morphological trait diversity of 140 woody plant species among seven temperate forests in North America representing 16.2°C variation in mean annual temperature (MAT), 2,115 mm variation in mean annual precipitation (MAP), and from 10 to 68 co-occurring species. We used untargeted metabolomics methods based on data generated with liquid chromatography-tandem mass spectrometry to identify, classify, and compare 13,480 unique foliar metabolites and to quantify the metabolomic similarity of species in each community with respect to the whole metabolome and each of five broad classes of metabolites. In addition, we compiled morphological trait data from existing databases and field surveys for three commonly measured traits (specific leaf area [SLA], wood density, and seed mass) for comparison with foliar metabolomes. We found that chemical defense strategies and growth and allocation strategies reflected by these traits largely represented orthogonal axes of variation. In addition, functional dispersion of SLA increased with MAP, whereas functional richness of wood density and seed mass increased with MAT. In contrast, chemical similarity of co-occurring species decreased with both MAT and MAP, and metabolite richness increased with MAT. Variation in metabolite richness among communities was positively correlated with species richness, but variation in mean chemical similarity was not. Our results are consistent with the hypothesis that plant metabolomes play a more important role in community assembly in wetter and warmer climates, even at temperate latitudes, and suggest that metabolomic traits can provide unique insight to studies of trait-based community assembly.

Tropical land-use change alters trait-based community assembly rules for dung beetles and birds

Tropical rainforest disturbance and conversion are critical drivers of biodiversity loss. A key knowledge gap is understanding the impacts of habitat modification on mechanisms of community assembly, which are predicted to respond differently between taxa and across spatial scales. We use a null model approach to detect trait assembly of species at local- and landscape-scales, and then subdivide communities with different habitat associations and foraging guilds to investigate whether the detection of assembly mechanisms varies between groups. We focus on two indicator taxa, dung beetles and birds, across a disturbance gradient of primary rainforest, selectively logged rainforest, and oil palm plantations in Borneo, Southeast Asia. Random community assembly was predominant for dung beetles across habitats, whereas trait convergence, indicative of environmental filtering, occurred across the disturbance gradient for birds. Assembly patterns at the two spatial scales were similar. Subdividing for habitat association and foraging guild revealed patterns hidden when focusing on the overall community. Dung beetle forest specialists and habitat generalists showed opposing assembly mechanisms in primary forest, community assembly of habitat generalists for both taxa differed with disturbance intensity, and insectivorous birds strongly influenced overall community assembly relative to other guilds. Our study reveals the sensitivity of community assembly mechanisms to anthropogenic disturbance via a shift in the relative contribution of stochastic and deterministic processes. This highlights the need for greater understanding of how habitat modification alters species interactions and the importance of incorporating species’ traits within assessments.

Intraspecific Trait Variation Dilutes Deterministic Processes in Community Assembly of Arid Shrubs across Multiple Scales

Trait-based approaches present a promising avenue for improving our understanding of species coexistence and community assembly, while intraspecific trait variation (ITV) across different spatial scales is important in trait-based community assembly mechanisms, especially in extreme environments. In this study, we focused on the functional diversity and community assembly patterns of a desert community across different spatial scales and investigated whether ITV plays a significant role in community assembly processes in arid habitats. A 50 m × 50 m plot with different small quadrats was established in a typical desert community at the transition zone between the Tengger Desert and Loess Plateau in China. A total of 14 traits were selected to assess the trait-based functional diversity and assembly processes in the community. We found that functional diversity showed different patterns when considering ITV and related to different types of traits (chemical traits or morphological traits) and some soil factors (pH and nitrate nitrogen). Plant communities in this study showed stochastic distribution patterns and similar functional diversity patterns based on functional trait approaches, regardless of spatial scales. Also, the effect of ITV on community assembly did not show more effect with increasing scales. These results indicated that ITV diluted deterministic processes in community assembly across scales in arid habitats.

Optimal Community Assembly Related to Leaf Economic- Hydraulic-Anatomical Traits.

Multi-dimensional trait mechanisms underlying community assembly at regional scales are largely unclear. In this study, we measured leaf economic, hydraulic and anatomical traits of 394 tree species from tropical to cold temperate forests, from which we calculated the leaf trait moments (mean, variance, skewness, and kurtosis) using community-weighted methods. Economic and hydraulic traits were decoupled at the species level, but coupled at the community level, and relationships between leaf traits in observed communities were stronger than that in null communities, suggesting that the adaptive mechanisms of plant species may be different. Furthermore, leaf economic traits were distributed more evenly across species occupying communities with lower temperature and precipitation, whereas hydraulic traits were distributed more evenly under lower water availability. This suggests that limiting similarity of specific leaf traits within communities would be enhanced when related-resources are limited, and highlights the independent assembly of leaf economics and hydraulic traits in terms of functional evenness. Importantly, the moments of leaf economic and hydraulic traits of observed communities explained more variation in ecosystem productivity than that of null communities, indicating ecosystem productivity depended on trait-based community assembly. Our results highlight the principles of community assembly regarding multi-dimensionsional traits in natural forests at a regional scale.

Trait-based community assembly of submersed macrophytes subjected to nutrient enrichment in freshwater lakes: Do traits at the individual level matter?

Abstract Understanding how functional traits distributed across ecological scales as well as environmental gradients are central issues of trait-based assembly processes. However, whether environmental filters act on individuals or species mean traits remains poorly tested. Here, we measured four functional traits – shoot height, specific leaf area, lamina thickness, and leaf dry mass content – of 4432 individuals from 30 submersed macrophyte species across 26 lakes in south China, covering a broad nutrient gradient. We partitioned trait variances into four nested ecological scales (i.e., region, community, species, individual) and assessed how the internal and external filters structured the submersed macrophyte community, either through acting on individual or on species mean traits, and how these processes related to nutrient enrichment. For the four tested traits, 13–60% of trait variability occurred within species (individual level), while 35–86% occurred among species (species level), followed by community and regional level. Species turnover contributed most to the community-wide variance along the nutrient gradient caused considerable intraspecific variations of shoot height. We found significant strong internal filtering effects on the submersed macrophyte community, which increased towards higher nutrient levels. The external filtering effects were only observed at individual level, with lower shoot height, specific leaf area, and leaf dry mass content than expected at low nutrient levels, and lower lamina thickness than expected at high nutrient levels. Our study provides new insight into the assembly processes by showing that niche overlap (i.e., intraspecific interaction) and niche differentiation (i.e., interspecific interaction) can simultaneously occur in different functional traits, both potentially promoting local species diversity. We conclude that an individual trait-based approach can help to detect assembly processes within and among lakes.

Trait-based community assembly of epiphytic diatoms in saline astatic ponds: a test of the stress-dominance hypothesis

The stress dominance hypothesis (SDH) postulates that strong environmental gradients drive trait convergence in communities over limiting similarity. Previous studies, conducted mostly with terrestrial plant communities, found controversial evidence for this prediction. We provide here the first test for SDH for epiphytic diatoms. We studied community assembly in diatom communities of astatic ponds. These water bodies serve as a good model system for testing SDH because they exhibit stress gradients of various environmental factors. Functional diversity of diatom communities was assessed based on four traits: (1) combined trait reflecting the trade-off between stress tolerance and competitive dominance, (2) cell size, (3) oxygen requirement and (4) N-uptake strategy. According to our results, salinity, pH and the width of the macrophyte belt appeared as significant predictors of the trait convergence/divergence patterns presumably acting through influencing the availability of carbon dioxide and turbidity. Lower trait diversity was found in turbid, more saline and more alkaline ponds and functional diversity was higher in transparent, less saline and less alkaline ponds. Overall, our results supported the stress dominance hypothesis. In habitats representing increased environmental stress, environmental filtering was the most important community assembly rule, while limiting similarity became dominant under more favourable conditions.

Trait-based community assembly and succession of the infant gut microbiome

The human gut microbiome develops over early childhood and aids in food digestion and immunomodulation, but the mechanisms driving its development remain elusive. Here we use data curated from literature and online repositories to examine trait-based patterns of gut microbiome succession in 56 infants over their first three years of life. We also develop a new phylogeny-based approach of inferring trait values that can extend readily to other microbial systems and questions. Trait-based patterns suggest that infant gut succession begins with a functionally variable cohort of taxa, adept at proliferating rapidly within hosts, which gradually matures into a more functionally uniform cohort of taxa adapted to thrive in the anoxic gut and disperse between anoxic patches as oxygen-tolerant spores. Trait-based composition stabilizes after the first year, while taxonomic turnover continues unabated, suggesting functional redundancy in the traits examined. Trait-based approaches powerfully complement taxonomy-based approaches to understanding the mechanisms of microbial community assembly and succession.

Conservation of Species- and Trait-Based Modeling Network Interactions in Extremely Acidic Microbial Community Assembly.

Understanding microbial interactions is essential to decipher the mechanisms of community assembly and their effects on ecosystem functioning, however, the conservation of species- and trait-based network interactions along environmental gradient remains largely unknown. Here, by using the network-based analyses with three paralleled data sets derived from 16S rRNA gene pyrosequencing, functional microarray, and predicted metagenome, we test our hypothesis that the network interactions of traits are more conserved than those of taxonomic measures, with significantly lower variation of network characteristics along the environmental gradient in acid mine drainage. The results showed that although the overall network characteristics remained similar, the structural variation was significantly lower at trait levels. The higher conserved individual node topological properties at trait level rather than at species level indicated that the responses of diverse traits remained relatively consistent even though different species played key roles under different environmental conditions. Additionally, the randomization tests revealed that it could not reject the null hypothesis that species-based correlations were random, while the tests suggested that correlation patterns of traits were non-random. Furthermore, relationships between trait-based network characteristics and environmental properties implied that trait-based networks might be more useful in reflecting the variation of ecosystem function. Taken together, our results suggest that deterministic trait-based community assembly results in greater conservation of network interaction, which may ensure ecosystem function across environmental regimes, emphasizing the potential importance of measuring the complexity and conservation of network interaction in evaluating the ecosystem stability and functioning.

Applying trait-based method to investigate the relationship between macrophyte communities and environmental conditions in a eutrophic freshwater lake, China

Trait-based community assembly analysis, which links the plant traits to the variation of community composition along environmental gradients, has potential to improve the understanding of the impacts of eutrophication on macrophytes and responding process. In this article, we pioneered the use of RLQ and Fourth-Corner methods that establish in a quantitative way the link between macrophyte traits, macrophyte community and water quality in a eutrophic shallow lake, eastern China. A total of 9 environmental variables and 11 macrophyte traits were included in the analysis. We found that total phosphorus in water (25.7%, the contribution to total inertia in RLQ analysis), suspended solids (20.7%), water transparency (17.1%) and Chlorophyll a (14.0%) were the main environmental variables that were associated the macrophyte traits matrix. Among macrophyte traits, life form (15.7%), responded to the environmental conditions the most, followed by leaf nitrogen (13.8%) and specific leaf area (13.6%). The correlation between macrophyte traits and environmental gradients showed that macrophytes with higher leaf nitrogen and higher specific leaf area grew at locations with clear water condition, better water transparency and with less total phosphorus, Chlorophyll a and suspended solids in this shallow eutrophic lake. The results suggested that the leaf nitrogen and specific leaf area of macrophytes had a trend to decrease with the increasing environmental stresses caused by eutrophication. Moreover, we highlighted that total phosphorus in water should be prior considered for the future macrophyte conservation and restoration in this lake.

Predicting trait-environment relationships for venation networks along an Andes-Amazon elevation gradient.

Understanding functional trait-environment relationships (TERs) may improve predictions of community assembly. However, many empirical TERs have been weak or lacking conceptual foundation. TERs based on leaf venation networks may better link individuals and communities via hydraulic constraints. We report measurements of vein density, vein radius, and leaf thickness for more than 100 dominant species occurring in ten forest communities spanning a 3,300m Andes-Amazon elevation gradient in Peru. We use these data to measure the strength of TERs at community scale and to determine whether observed TERs are similar to those predicted by physiological theory. We found strong support for TERs between all traits and temperature, as well weaker support for a predicted TER between maximum abundance-weighted leaf transpiration rate and maximum potential evapotranspiration. These results provide one approach for developing a more mechanistic trait-based community assembly theory.

A critical issue in model-based inference for studying trait-based community assembly and a solution.

Statistical testing of trait-environment association from data is a challenge as there is no common unit of observation: the trait is observed on species, the environment on sites and the mediating abundance on species-site combinations. A number of correlation-based methods, such as the community weighted trait means method (CWM), the fourth-corner correlation method and the multivariate method RLQ, have been proposed to estimate such trait-environment associations. In these methods, valid statistical testing proceeds by performing two separate resampling tests, one site-based and the other species-based and by assessing significance by the largest of the two p-values (the pmax test). Recently, regression-based methods using generalized linear models (GLM) have been proposed as a promising alternative with statistical inference via site-based resampling. We investigated the performance of this new approach along with approaches that mimicked the pmax test using GLM instead of fourth-corner. By simulation using models with additional random variation in the species response to the environment, the site-based resampling tests using GLM are shown to have severely inflated type I error, of up to 90%, when the nominal level is set as 5%. In addition, predictive modelling of such data using site-based cross-validation very often identified trait-environment interactions that had no predictive value. The problem that we identify is not an “omitted variable bias” problem as it occurs even when the additional random variation is independent of the observed trait and environment data. Instead, it is a problem of ignoring a random effect. In the same simulations, the GLM-based pmax test controlled the type I error in all models proposed so far in this context, but still gave slightly inflated error in more complex models that included both missing (but important) traits and missing (but important) environmental variables. For screening the importance of single trait-environment combinations, the fourth-corner test is shown to give almost the same results as the GLM-based tests in far less computing time.

Trait-Based Community Assembly along an Elevational Gradient in Subalpine Forests: Quantifying the Roles of Environmental Factors in Inter- and Intraspecific Variability.

Understanding how communities respond to environmental variation is a central goal in ecology. Plant communities respond to environmental gradients via intraspecific and/or interspecific variation in plant functional traits. However, the relative contribution of these two responses to environmental factors remains poorly tested. We measured six functional traits (height, leaf thickness, specific leaf area (SLA), leaf carbon concentration (LCC), leaf nitrogen concentration (LNC) and leaf phosphorus concentration (LPC)) for 55 tree species occurring at five elevations across a 1200 m elevational gradient of subalpine forests in Yulong Mountain, Southwest China. We examined the relative contribution of interspecific and intraspecific traits variability based on community weighted mean trait values and functional diversity, and tested how different components of trait variation respond to different environmental axes (climate and soil variables). Species turnover explained the largest amount of variation in leaf morphological traits (leaf thickness and SLA) across the elevational gradient. However, intraspecific variability explained a large amount of variation (49.3%–76.3%) in three other traits (height, LNC and LPC) despite high levels of species turnover. The detection of limiting similarity in community assembly was improved when accounting for both intraspecific and interspecific variability. Different components of trait variation respond to different environmental axes, especially soil water content and climatic variables. Our results indicate that intraspecific variation is critical for understanding community assembly and evaluating community response to environmental change.

Commonness and rarity determinants of woody plants in different types of tropical forests

The aim of this work is to examine whether there exists a link between local and landscape patterns of species commonness, and if these are related to morphological traits in tropical plant communities. The Madidi region (Bolivian tropical Andes) is selected as study location. We estimated local and landscape commonness, rarity classes, height, diameter, number of stems, and habit for >2,300 species. We employed correlations to evaluate the relationship between local scale commonness and landscape scale commonness. We performed ANCOVA and multinomial logistic regressions to predict commonness and rarity variables from the morphological traits. We repeated the analyses for six different forest types, including dry forests and wet forests along a 3,477 m elevation gradient. We found a positive relationship between local and landscape commonness in all forest types. Additionally, we found that, plant height influences the local and landscape commonness, and that the apportioning of species into rarity classes depends greatly on the species habit and, at lesser degree, on the number of stems. Our main conclusions are: (1) Approaches to commonness and rarity based on abundance only or occurrence only could summarize most of the relevant information to characterize commonness and rarity patterns: both approaches, in practice, do not supply independent information. (2) The species traits determine which species are rare and which ones are common, which indicates that commonness and rarity patterns are the result of non-neutral trait-based community assembly processes.

Context-dependent assembly rules and the role of dominating grasses in semi-natural abandoned sub-Mediterranean grasslands

We investigated fine-scale patterns of trait-based community assembly in calcareous grasslands of the Central Apennines, Italy. We used the habitat template of environmentally contrasting north-facing and south-facing slopes of a mountain valley to understand mechanisms that contribute to species coexistence (i.e. the persistence of diversity) after cessation of previous land use practices. Firstly, we tested late successional dominating grasses (Sesleria nitida, Brachypodium rupestre and Bromopsis erectus) for their ability to serve as biotic filtering effects on the diversity of subordinate species in plant communities. Secondly, we analyzed fine-scale trait-based (i.e. species-level traits related to competition, regeneration, establishment, dispersal, and flowering) community assembly of subordinate species in absence of dominant grass. We found that assembly rules for traits related to the same life-history process were mostly consistent within habitats. Further we established that within habitats the traits related to different life-history processes can show different assembly rules. For example, while generative regeneration traits (seed mass) may show convergence pattern, divergence was inferred for the vegetative (clonal) regeneration traits. Depending on traits, the assembly rules can be similar or contrasting in different habitats. We conclude that our finding of non-random assembly in the majority of investigated traits emphasizes the importance of hierarchical exclusion of strong biotic filters when searching for trait-based assembly rules in abandoned grasslands. Thus, for nature conservation purposes, disturbance appears to be the process that is most important in driving the survival of subordinate species by the exclusion of biotic filters. Subsequently, a multitude of trait-based mechanisms allow for coexistence of the subordinate species. These mechanisms depend on habitats and traits and thus may vary from community to community, indicating that heterogeneous landscapes might support multiple processes of coexistence.