Plant Community Metrics Research Articles

Differential responses of soil microbial biomass, diversity, and compositions to altitudinal gradients depend on plant and soil characteristics

Alt'itudinal gradients strongly affect plant biodiversity, but the effects on microbial patterns remain unclear, especially in the large scale. We therefore designed an altitudinal gradient experiment that covered three climate zones to monitor soil microbial community dynamics and to compare those with plant and soil characteristics. Illumina sequencing of the 16S rRNA gene and ITS gene was used to analyze soil microbial (bacterial and fungal) diversity and composition, and fumigation–extraction was used to determine microbial biomass; the plant community metrics (i.e., percent cover, Shannon-Wiener, grass biomass, and carbon/nitrogen in leaf and biomass) and soil properties (i.e., soil moisture, soil temperature, bulk density, organic carbon, total nitrogen, and available nitrogen) were determined. The results showed that carbon/nitrogen in microbial biomass was higher at medium altitude and was positively related to carbon and nitrogen in both soil and grass biomass along the altitudinal gradients. Soil bacterial alpha diversity was significantly higher at medium altitude but fungal alpha diversity did not affected by altitudinal gradients; the effect of altitudinal gradients on bacterial beta diversity was larger than that on fungal beta diversity, although both groups were significantly affected by altitudinal gradients. Moreover, Alpha-proteobacteria, Beta-proteobacteria, and Gemmatimonadetes were significantly more abundant in higher altitude than in lower altitude, both Acidobacteria and Actinobacteria significantly declined with increasing altitude; other bacterial taxa such as Chloroflexi, Nitrospirae, Gamma-proteobacteria, and Delta-proteobacteria were significantly higher at medium altitudes. For fungal taxa, Basidiomycota and Ascomycota were the dominant phyla and responded insignificantly to the altitudinal gradients. The responses of microbial alpha diversity were mostly associated with plant Shannon index, organic carbon, and total nitrogen, whereas microbial beta diversity and composition mainly depended on soil moisture and temperature. Overall, these results suggest that soil bacteria rather than fungi can reflect changes in plant and soil characteristics along altitudinal gradients.

Environmental watering for vegetation diversity outcomes must account for local canopy conditions

AbstractHydrology is widely considered to be the dominant driver of understorey vegetation dynamics in arid and semiarid riparian ecosystems. Consequently, environmental watering is often a key approach to restoring and promoting riparian vegetation diversity. Few studies however have considered the role of local factors, for example, shading or litter accumulation, on vegetation responses to flow and how these may influence the outcomes of watering actions. Knowledge concerning modifying effects of local canopy factors on vegetation responses to watering is needed to guide environmental water planning (e.g., setting objectives and targets) and delivery (e.g., timing and duration of managed flows). We conducted a greenhouse experiment to investigate the effects of shade and litter, and their interaction, on plant communities establishing from riparian soil seed banks, collected from the northern Murray–Darling Basin, under a range of hydrological conditions. We found that shade had a positive influence on the abundance, diversity, and reproduction of establishing plant communities under dry conditions but a negative, or null effect, under wet conditions. Litter exerted strong negative effects on plant community metrics under all hydrological conditions. Some understorey species emerged as hardy generalists capable of establishment under a range of conditions whereas others had more specific requirements. Our results highlight the importance of canopy structure for riparian understorey vegetation diversity and dynamics at both local and landscape scales. Land and water management practices seeking to protect or restore vegetation diversity in these systems must therefore take such local factors into account when planning and evaluating interventions.

Residents’ perceptions and valuations of urban wastelands are influenced by vegetation structure

Among the different urban green spaces, wastelands are valuable spaces for conserving urban biodiversity. By hosting wild and spontaneous vegetation, wastelands can promote the contact citizens have with nature. However, lack of regular management can lead to negative perceptions. In this study we assessed perceptions, valuations and uses of wastelands by residents in two cities in the centre of France. We tested whether preferences for wastelands depended on where wastelands were located in the city, plant community characteristics or resident characteristics. The study investigated 18 wastelands, in three successional stages (initial grassland, intermediate grassland and shrubbery stages) and located in three categories of distance from the city centre (downtown, suburban, periurban). Vegetation was sampled in each wasteland and several plant community metrics were calculated. A total of 72 residents (4 per wasteland) living in the vicinity of the wastelands were interviewed about their use, valuations and perceptions of wastelands. Based on qualitative and quantitative analyses, the results highlighted that a significant proportion of residents (36%) conducted various activities in wastelands and that perceptions and valuations of wastelands were diverse, ranging from either negative (when wastelands were perceived as wild or abandoned areas) or positive (when wastelands were considered as natural and recreational). Valuations strongly depended on the successional stage, with intermediate grassland-like wastelands being preferred. We found no effect of wasteland location in the city, whereas resident characteristics (age and gender) marginally influenced valuations. This study provides new insights into the determinants of perception and valuations of urban wastelands. Particularly, we suggest that intermediate grassland-like wastelands could be easily integrated into urban planning both for recreational activities and conserving biodiversity. Alternatively, awareness of the value of initial grassland-like and shrubbery wastelands should be raised to improve their acceptability.

Does structural connectivity influence tree species distributions and abundance in a naturally discontinuous tropical forest formation?

AbstractAimsThe study of naturally discontinuous forest systems could help further our understanding of the relative roles of abiotic factors and spatial connectivity in influencing species turnover and plant metacommunity structure, compared to continuous forest formations, where local communities are often arbitrarily defined and where ‘mass effects’ and source–sink dynamics tend to confound the roles of dispersal and environment. Here we studied a tropical montane landscape where old‐growth evergreen forest occurs as patchy formations in a matrix of natural grasslands, to test the influence of environment and connectivity on species turnover and woody plant metacommunity structure.LocationWestern and southern regions of the Upper Nilgiri Plateau, Western Ghats, southern India.MethodsWe sampled 85 vegetation plots located across a 600‐km2 landscape, assembled environmental data, constructed contrasting spatial connectivity models, including models for the effects of topography on structural connectivity, and used RDA‐based variation partitioning to assess the relative influence of environment and space on woody plant metacommunity structure.ResultsConsidering several environmental and multi‐scale spatial predictors, we could explain half of the variation in plant community structure. Environmental and habitat factors such as precipitation, temperature seasonality, elevation, fragment size and landscape context play a dominant role, explaining approximately 40% of variation. Spatial predictors based on Euclidean distance performed better than those that accounted for topographic resistance. Spatial predictors accounted for only 9% of the variation in plant metacommunity structure.ConclusionOur results support the species sorting paradigm of metacommunity structure, as abiotic effects and biotic interactions play dominant roles in influencing community structure and species turnover in these old‐growth forests, with a comparatively small influence of spatial connectivity. Effective management of woody species diversity would therefore require conservation of these forests across the range of environmental conditions under which they occur.

Differential organization of taxonomic and functional diversity in an urban woody plant metacommunity

AbstractQuestionsUrban ecosystems present an opportunity to study ecological communities in the context of unprecedented environmental change. In the face of urban land conversion, ecologists observe new patterns of species composition, dominance, behaviour and dispersal. We propose a hypothetical socioeconomic template that describes a gradient in human investment in community composition to aid in organizing the human role in shaping urban biodiversity. We asked: (1) what is the relative magnitude of taxonomic and functional turnover of urban woody plant communities across different land‐use types; and (2) do land uses exhibiting higher intensity of human management of biodiversity support higher turnover over those with less human influence?LocationBaltimore, MD, USA (39°17′ N, 76°38′ W).MethodsWe examined patterns in woody plant biodiversity across 209 plots of different urban land uses. Six land‐use types were arranged along a gradient in the intensity through which humans are hypothesized to manage species composition at the plot scale. We calculated local, or α‐diversity, and compositional turnover, or β‐diversity, of taxonomic and functional diversity across plots within each land‐use type. We compared the magnitude of these biodiversity measures between land uses to test our conceptual template for how the intensity of human management can predict urban woody plant biodiversity.ResultsWe observed high taxonomic turnover in residential and commercial plots compared with vacant or open space land‐use areas. This was associated with a weaker, but similar, pattern in functional diversity. This was associated with low total abundance in residential and commercial plots. Furthermore, the number of unique species was extremely high in the same land‐use types.ConclusionsOur observations help explain why turnover can be high in heavily managed plots relative to vacant land. In patches without heavy human management, we found low levels of turnover. This highlights the importance of assessing diversity both locally and at the level of turnover between patches. Management and policy can benefit from the perspective embodied in the conceptual approach tested here.

Soil bacterial community dynamics reflect changes in plant community and soil properties during the secondary succession of abandoned farmland in the Loess Plateau

The effects of natural succession on plant communities and soil variables have been established, but changes in microbial communities and their response to plants and soils have not been well characterized in secondary succession. We investigated the changes in soil properties and plant and soil microbial communities during the secondary succession on abandoned cropland in the Loess Plateau of China using high-throughput sequencing of the 16S rRNA gene. The study analyzed a chronosequence of farmland undergoing spontaneous succession after being abandoned for 0 (farmland), 5, 10, 15, 20 and 30 years(y). Plant community metrics including percent cover, and above/belowground biomass, first decreased in the initial stage (<10 y) and then increased during the succession. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant phyla of soil bacteria across all succession. Bacterial communities transitioned from Acidobacteria-dominant to Proteobacteria-dominant communities during the 30 years of succession. Levels of soil organic carbon (C), total nitrogen (N), nitrate N and bacterial diversity were lower soon (<5 years) after abandonment compared to the farmland, but they could recover to farmland levels after 15–20 years and were much improved after continued succession. Plant and bacterial community diversities (Shannon index and species richness) changed along successional time, but they showed different patterns, suggesting an incongruous process between plant and microbial succession. Organic C, total N, available N, and available P contents were significantly correlated with the abundance of most bacterial groups and the Shannon index, indicating the dependence of bacterial community diversity on soil nutrient supply.

The role of distance and habitat specificity in bryophyte and perennial seed plant metacommunities in arid scrubland fragments

AbstractQuestionsWhat are the relative roles of (1) environmental niche partitioning (especially along soil chemistry gradients), (2) effective dispersal, and (3) landscape characteristics in structuring species assemblies of bryophyte and seed plant metacommunities?LocationEbro river basin, NE Spain.MethodsWe sampled biological soil crust (BSC) bryophytes and perennial seed plants from 54 plots in ten fragments of native vegetation from two contiguous landscapes with contrasting agricultural matrix types. Each plot was characterized with respect to soil electrical conductivity (EC, a proxy for presence of gypsum and halite), pH, vegetation cover and aspect. We used unconstrained ordinations to find the main floristic gradients and evaluated their relationship with environmental variables using Kendall correlations. We studied the spatial structure of floristic dissimilarities for bryophyte and seed plant communities by using multiple regression models on distance matrices (MRM), and individual species' responses by estimating species' densities along environmental gradients. We estimated effective isolation between plots within landscapes by means of partial MRM.ResultsWe found 60 bryophyte and 57 seed plant species. Compositional dissimilarities were spatially structured. DCA showed clear floristic segregation of the two landscapes. The soil EC gradient was the main variable explaining compositional variation in both plant metacommunities, followed by soil pH. The effect of geographic distance between plots differed significantly between landscapes and matrix types, and was larger for seed plants than for bryophytes.ConclusionsOnly a handful of BSC bryophyte species can be regarded as either true gypsofuges or true gypsophiles. Gypsophilous bryophytes are fewer and less strongly associated with gypsum‐rich sites than co‐existing perennial seed plants. Overall, BSC bryophyte communities vary less over similar distances than corresponding seed plant communities, most likely due to higher dispersal ability. We argue that the topographically complex landscape of a less modified agricultural matrix imposes more ‘friction’ to bryophyte dispersal than a smoother landscape with a more intensely human‐modified matrix. Effective conservation of fragmented arid agricultural landscapes must take into account the sensitivity of the biota to fragment intrinsic conditions, the properties and the management practices that shaped the landscape.

Selective manipulation of a non-dominant plant and its herbivores affects an old-field plant community

Competition and herbivory can interact to influence the recovery of plant communities from disturbance. Previous attention has focused on the roles of dominant plant species in structuring plant communities, leaving the roles of subordinate species often overlooked. In this study, we examined how manipulating the density of a subordinate plant species, Solanum carolinense, and its insect herbivores influenced an old-field plant community in northern Florida following a disturbance. Five years following the disturbance, the initial densities of S. carolinense planted at the start of the experiment negatively influenced total plant cover and species diversity, and the cover of some grasses (e.g., Paspalum urvillei) and forbs (e.g., Rubus trivalis). Selectively removing herbivores from S. carolinense increased S. carolinense abundance (both stem densities and cover), increased the total cover of plants in the surrounding plant community, and affected plant community composition. Some plant species increased (e.g., Digitaria ciliaris, Solidago altissima) and others decreased (e.g., Paspalum notatum, Cynodon dactylon) in cover in response to herbivore removal. Herbivore effects on plant community metrics did not depend on S. carolinense density (no significant herbivory by density interaction), suggesting that even at low densities, a reduction of S. carolinense herbivores can influence the rest of the plant community. The recovery of the plant community was context dependent, depending on site- and plot-level differences in underlying environmental conditions and pre-disturbance plant community composition. We demonstrate that the density of and herbivory on a single subordinate plant species can affect the structure of an entire plant community.

Temporal Trends of Ecosystem Development on Different Site Types in Reclaimed Boreal Forests

Forest development after land reclamation in the oil sands mining region of northern Alberta, Canada was assessed using long-term monitoring plots from both reclaimed and natural forests. The metrics of ecosystem development analyzed included measures of plant community structure and composition and soil nutrient availability. Early seral reclamation plots were grouped by site type (dry and moist-rich) and age categories, and these were compared with mature natural forests. There were few significant differences in ecosystem metrics between reclamation site types, but natural stands showed numerous significant differences between site types. Over time, there were significant changes in most plant community metrics such as species richness and cover of plant community groups (e.g., forbs, shrubs, and non-native species), but these were still substantially different from mature forests 20 years after reclamation. Available soil nitrogen did not change over time or by reclamation site type but available soil phosphorus did, suggesting that phosphorus may be a more suitable indicator of ecosystem development. The significant temporal changes in these reclaimed ecosystems indicate that studies of ecosystem establishment and development on reclaimed areas should be conducted over the long-term, emphasizing the utility of monitoring using long-term plot networks.

Effects of species' similarity and dominance on the functional and phylogenetic structure of a plant meta-community.

Different assembly processes drive the spatial structure of meta-communities (beta-diversity). Recently, functional and phylogenetic diversities have been suggested as indicators of these assembly processes. Assuming that diversity is a good proxy for niche overlap, high beta-diversity along environmental gradients should be the result of environmental filtering while low beta-diversity should stem from competitive interactions. So far, studies trying to disentangle the relative importance of these assembly processes have provided mixed results. One reason for this may be that these studies often rely on a single measure of diversity and thus implicitly make a choice on how they account for species relative abundances and how species similarities are captured by functional traits or phylogeny. Here, we tested the effect of gradually scaling the importance of dominance (the weight given to dominant vs. rare species) and species similarity (the weight given to small vs. large similarities) on resulting beta-diversity patterns of an alpine plant meta-community. To this end, we combined recent extensions of the Hill numbers framework with Pagel's phylogenetic tree transformation approach. We included functional (based on the leaf-height-seed spectrum) and phylogenetic facets of beta-diversity in our analysis and explicitly accounted for effects of environmental and spatial covariates. We found that functional beta-diversity, was high when the same weight was given to dominant vs. rare species and to large vs. small species' similarities. In contrast, phylogenetic beta-diversity was low when greater weight was given to dominant species and small species' similarities. Those results suggested that different environments along the gradients filtered different species according to their functional traits, while, the same competitive lineages dominated communities across the gradients. Our results highlight that functional vs. phylogenetic facets, presence-absence vs. abundance structure and different weights of species' dissimilarity provide complementary and important information on the drivers of meta-community structure. By utilizing the full extent of information provided by the flexible frameworks of Hill numbers and Pagel's tree transformation, we propose a new approach to disentangle the patterns resulting from different assembly processes.

Regional metacommunities in two coastal systems: spatial structure and drivers of plant assemblages

AbstractAimBiogeographical patterns in metacommunities are still poorly understood, and different processes are expected to occur in different habitats. We analysed the regional plant metacommunities of coastal habitats to test whether (1) the influence of space and climate differs between two habitats differentiated along the seashore–inland gradient, and (2) regional variation in species composition of these habitats can be ascribed to different metacommunity paradigms.LocationThe entire coast of the Iberian Peninsula, south‐western Europe.MethodsWe collected data on the plant species composition of coastal sites on sand dunes across 3000 km of coastline. The sites were classified into two habitats corresponding to shifting and stable sand dunes, and divided into three distinct geographical regions: Cantabrian, Atlantic and Mediterranean. We assessed the geographical structure of the species composition using ordination, estimates of species turnover and spatial autocorrelation. We then used multivariate models and variation partitioning to test the influence of climatic and spatial effects. Analyses were conducted for the whole data set and the geographical subsets.ResultsMetacommunities from shifting and stable dunes showed similar spatial patterns, with the highest species turnover occurring in the Mediterranean region. Similarities between communities that were nearer each other (typically &lt; 100 km) were weaker in shifting than in stable dunes, although the distance decay for sites that were further apart was similar in both habitats. Variation in species composition in shifting dunes was mainly explained by distance and climate, while in stable dunes the effect of climate was clearly dominant. The observed differences were relatively consistent across geographical regions.Main conclusionsDistinct processes structure the metacommunities in two dune habitats differentiated along the seashore–inland gradient. Communities of shifting dunes seem to be structured by an interplay of neutral or patch‐dynamic processes and to a lesser degree by species sorting. In contrast, communities of stable dunes are mainly governed by species sorting in response to climatic gradients. These results highlight the importance of differentiating habitats according to local ecological factors when analysing regional patterns in metacommunities.

Connectivity and propagule sources composition drive ditch plant metacommunity structure

The fragmentation of agricultural landscapes has a major impact on biodiversity. In addition to habitat loss, dispersal limitation increasingly appears as a significant driver of biodiversity decline. Landscape linear elements, like ditches, may reduce the negative impacts of fragmentation by enhancing connectivity for many organisms, in addition to providing refuge habitats. To characterize these effects, we investigated the respective roles of propagule source composition and connectivity at the landscape scale on hydrochorous and non-hydrochorous ditch bank plant metacommunities. Twenty-seven square sites (0.5 km2 each) were selected in an agricultural lowland of northern France. At each site, plant communities were sampled on nine ditch banks (totaling 243 ditches). Variables characterizing propagule sources composition and connectivity were calculated for landscape mosaic and ditch network models. The landscape mosaic influenced only non-hydrochorous species, while the ditch network impacted both hydrochorous and non-hydrochorous species. Non-hydrochorous metacommunities were dependent on a large set of land-use elements, either within the landscape mosaic or adjacent to the ditch network, whereas hydrochorous plant metacommunities were only impacted by the presence of ditches adjacent to crops and roads. Ditch network connectivity also influenced both hydrochorous and non-hydrochorous ditch bank plant metacommunity structure, suggesting that beyond favoring hydrochory, ditches may also enhance plant dispersal by acting on other dispersal vectors. Increasing propagule sources heterogeneity and connectivity appeared to decrease within-metacommunity similarity within landscapes. Altogether, our results suggest that the ditch network's composition and configuration impacts plant metacommunity structure by affecting propagule dispersal possibilities, with contrasted consequences depending on species' dispersal vectors.

Conservation implications of long-term changes detected in a lowland heath plant metacommunity

Conservation management that is focused on the scale of individual habitat patches rarely considers the implications for conservation of metacommunities at the regional scale. Here we examine the conservation implications of long-term changes identified in a vascular plant metacommunity associated with lowland heathland in Dorset, UK. This was achieved by re-surveying 150 patches that were first surveyed in the 1930s and assessing changes in species distributions, diversity, community composition and metacommunity structure. Results were compared for two sets: (i) all remaining heathland patches and (ii) intact heaths, excluding partly degraded sites. Overall, patterns of change were similar for the two sets. Values of γ- and α-diversity both decreased over time as individual patches shifted towards either woodland or improved grassland communities. However, only the intact heaths set exhibited a significant decrease in β-diversity. Both sets lost metacommunity structure over time, suggesting a change in underlying processes. These changes were attributable both to management regimes adopted at local sites, relating to their differing ownership, and to wider processes of environmental change. These results highlight the need to place site-based conservation actions in the context of regional-scale processes, to ensure the long-term conservation of metacommunity structure and function.

Effects of Recreational Traffic on Alpine Plant Communities in the Northern Canadian Rockies

Recreational activities in alpine areas have been increasing in recent decades, creating the need to improve our understanding of the impacts of these activities and how they are best managed. We explored impacts of recreational trail use on dry alpine meadows in the northern Canadian Rockies of Alberta. Data collected in 142 plots (0.5 m × 1 m) were used to compare plant community metrics among (1) a recreational trail, (2) intact tundra meadows (undisturbed), and (3) sparsely vegetated gravel steps formed by frost disturbance (naturally disturbed). As compared to undisturbed tundra, trails had substantially lower cover of vascular plants (4% vs. 35%), lichen (0% vs. 10%), and cryptogamic crust (0% vs. 4%); trails also had lower species richness (7 vs. 11 species per plot), but greater soil compaction (2.75 vs. 1.25 kg cm-2). Trails differed from natural gravel steps, which had three times more biotic cover and different composition. This highlights the difference in effects of human and natural disturbance. Positive feedback effects of trampling in tundra ecosystems may lead to altered environmental conditions, including decreased infiltration capacity and nutrient cycles in soils, and more extreme temperatures at the soil surface. These feedbacks could inhibit regeneration of abandoned trails.

Vegetative Forage Quality and Moist-soil Management on Wetlands Reserve Program Lands in Mississippi

The Wetland Reserve Program (WRP) prescribes management of vegetation in moist-soil wetlands for waterfowl and other wildlife. This study used a block design on 18 sites in the Mississippi Alluvial Valley (MAV) in Mississippi to evaluate effectiveness of management prescriptions. Objectives were to determine appropriate timing of vegetation surveys and whether vegetation community metrics on private lands differed among management strategies (2008–2009): 1) active (e.g., annual soil disturbance), early drawdown of standing water (i.e., by 15 June), 2) active, late drawdown (≥3 weeks after early drawdown), and 3) passive, natural evaporation. A Vegetative Forage Quality Index (VFQI) was developed to assess quality of plant communities as forage for waterfowl. The study examined VFQI, plant community diversity and richness, percent (%) occurrence of grass, % woody species, and mean number of plant life-forms among management categories (α = 0.10). Plant community metrics were measured June–October but only October metrics revealed differences in both years (p ≤ 0.09). Active-early had the greatest VFQI, diversity, mean number of plant life-forms, and percent abundance of grasses in October 2008 and 2009 (p ≤ 0.07). Results suggest that quality forage for waterfowl may be achieved through active management with early draw-down.

White-Tailed Deer (Odocoileus virginianusZimm.) Herbivory in Herbaceous Plant Communities in Northeastern Illinois

ABSTRACT: Most studies of white-tailed deer (Odocoileus virginianus Zimm.) herbivory focus on a few forb species or single sites in forest plant communities. However, managers require assessments of herbivory impacts across varying deer densities and in multiple plant communities, including wetlands and savannas where there is limited knowledge about the impacts of deer on herbaceous vegetation. During 2008 and 2009, we investigated deer herbivory impacts at six forest preserves near Chicago, Illinois. We sampled 192 browse transects in two forest, two savanna, and two wetland sites; sites were paired within each plant community type based on deer density (i.e., high vs. low). We used plant community metrics (i.e., percent non-vegetated ground cover, species diversity and evenness, and floristic quality) to quantify and compare herbivory impacts on vegetation between preserves. We observed higher grass cover (0.001 < P < 0.012), lower species diversity (0.001 < P < 0.041), and lower floristic quality (0.0...

Species sorting dominates plant metacommunity structure in coastal dunes

It has long been thought that environmental factors determine plant community assembly, but it is now increasingly argued that geographic spatial processes such as dispersal may also matter. Notably, the metacommunity framework considers local communities to be linked by dispersal and different theories hereunder assign varying importance to dispersal limitation and local environmental species sorting. At present the relative importance of these factors across habitats, geographic regions, and spatial scales remains unclear. The present study assessed the relative importance of species sorting by the local environment and broader-scale geographic spatial processes for local plant species composition using a data set of 3924 plots from coastal dunes across a large region (Denmark). We used ordination to identify the main gradients in species composition, and Linear Mixed-Effects modelling (LME) to estimate the relative importance of local environment and multi-scale random geographic factors as determinants of floristic gradients. In addition, we assessed the dependence of species composition on local environment and geographic distance using Mantel tests. The LME analyses found local species sorting to be the dominant determinant in this metacommunity system, with soil moisture, pH, and fertility requirement patterns explaining ≥77% of the compositional gradients, while geographic factors accounted for ≤2%. Partial Mantel tests confirmed this finding, with 31.6% of the variation in species dissimilarity explained by environmental species sorting and just 1.6% by geographical distance. The apparently limited impact of dispersal limitation or other geographic spatial processes may reflect high habitat continuity and efficient dispersal by strong winds and ocean currents in the Danish coastal-dune metacommunity system.

Structure, composition and dynamics of a calcareous grassland metacommunity over a 70‐year interval

Summary1. Calcareous grasslands are communities of high conservation value, often characterized by high plant species richness. These grasslands have experienced a major decline in area throughout Europe, principally resulting from agricultural intensification. Although they have been the focus of extensive previous research, few attempts have been made to examine the long‐term dynamics of multiple communities at the landscape scale.2. To assess long‐term change in the structure and composition of a calcareous grassland metacommunity, 88 extant sites first surveyed by R. Good in the 1930s were resurveyed in 2009. Values of α‐, β‐ and γ‐diversity were compared between the two surveys, using a one‐way analysis of similarity (ANOSIM) and non‐metric multidimensional scaling. Elements of metacommunity structure (EMS) analysis was used to identify metacommunity structure, and changes in metacommunity composition were related to plant traits.3. Analyses indicated that α‐diversity increased over time, with mean (±SD) species richness per site increasing from 29.31 ± 7.65 in the 1930s to 40.18 ± 16.41 in 2009. No change in β‐diversity was recorded. However, γ‐diversity increased, with the total number of species rising from 219 in the 1930s to 280 in 2009. Species composition shifted over time, associated with a decline in ‘stress‐tolerant’ species typical of species‐rich calcareous grasslands, and an increase in species typical of mesotrophic grasslands. This was associated with an increase in mean Ellenberg N value, suggesting that eutrophication has been a driver of floristic change.4. Elements of metacommunity structure analysis indicated that the structure of this grassland plant metacommunity was Clementsian at both survey times, indicating species sorting. Metacommunity structure was stable over time, despite changes in α‐ and γ‐diversity. Analysis of potential structuring mechanisms revealed a significant influence of elevation.5. Synthesis. This investigation provides a rare example of the long‐term dynamics of a plant metacommunity. Results indicate that substantial change has occurred in the composition of calcareous grasslands during this time, both at local and regional scales. The investigation provides evidence of the impact of environmental change on immigration and extinction processes operating in calcareous grasslands at different scales, and highlights challenges for their future conservation.

Local and landscape influences on plant communities in playa wetlands

Summary1. Hydroperiod, wetland size and land use of watersheds surrounding wetlands have important individual influences on plant communities in wetlands. Our objectives were to determine the effect and relative importance of local and landscape factors on plant species richness, diversity and composition of different functional groups (i.e. total, wetland‐dependent, perennial, annual and exotic species) in recently inundated playa wetlands.2. We surveyed plant communities in 80 wet playas in the Southern High Plains, USA, and measured local factors: water depth, playa volume loss, sediment depth and playa area. We included landscape variables within 3 km: number of playas, edge density, percentage urban area and percentage Conservation Reserve Program area (CRP; conversion from highly erodible cropland to mostly introduced perennial grassland). We also recorded dominant land use as native grassland or cropland.3. Water depth negatively influenced all plant community metrics (i.e. richness, diversity and cover) while playa volume loss (sediment eroded from watershed filling the basin) had a negative influence on total, wetland‐dependent and perennial richness and cover. Playas with more cropland within their watersheds had greater annual and exotic richness and cover, suggesting that agricultural activities within playa watersheds have changed plant composition and facilitated biological invasion.4. Playa area was less important in predicting plant community metrics in playas. Although not as dominant as local variables, edge density had a positive influence on species richness. Other landscape factors such as number of playas, percentage urban area and percentage CRP area were less important and consistent among different plant community metrics.5. Synthesis and applications. Our results show that continued unsustainable sedimentation will result in loss of perennial species and promotion of exotic and annual species in playas. Watershed management to limit unsustainable sedimentation has the potential to maintain original playa plant communities dominated by perennial/native species and should also reduce the loss of playa functionality.

Do birds of a feather disperse plants together?

Summary 1. Dispersal of propagules by waterbirds is thought to be important for wetland plants because of the abundance of birds and their frequent movements among aquatic habitats. Differences in bird characteristics (size, movement, feeding ecology) were expected to lead to different outcomes for plant dispersal. 2. We investigated heterogeneity in plant dispersal by ducks (Anas superciliosa, Anas gracilis, Anas castanea). We calculated the probability of transport of viable seeds by germinating propagules retrieved from feathers and feet (epizoochory) and the contents of the oesophagus, gizzard and lower gut (endozoochory). 3. The abundance and richness of seeds carried internally and externally did not differ among sympatric bird species. We used estimates from the literature of movements of Anas species to approximate dispersal kernels for the transport of plant propagules. 4. Heterogeneity in the abundance and movement ecology of disperser species will result in differing patterns and degrees of connectivity for wetland plant metacommunities. Sedentary waterfowl are likely to have an important role in replenishing propagules and connecting aquatic metacommunities over small distances. Nomadic waterfowl may facilitate long-distance dispersal. We discuss the implications of differences between duck species in movement patterns for connectivity of aquatic plant metacommunities across landscapes.