Composition Of Plant Assemblages Research Articles

Exploring dynamics of floristic composition in Mediterranean grasslands: a case study from Sardinia, Italy

Mediterranean grasslands stand out as biodiversity hotspots due to their inclusion of diverse habitats that foster a remarkable range of biological diversity, characterized by inter-annual variability of floristic composition. This study aims to assess the inter-annual dynamics of the floristic composition in a grassland within a typical silvopastoral system in the Mediterranean basin, within the framework of rainfall variability. The study was performed on a farm representative of Mediterranean silvopastoral systems in Central-Western Sardinia (Italy). Vegetation surveys started in the spring of 2018 and concluded in the spring of 2022. They were conducted annually in the spring (S) and winter (W) seasons, using the point quadrat method along eight permanent transects. The dynamics of floristic composition were compared within and between years in terms of variability of specific percentage contribution (CSP) of each plant species. The results highlighted substantial differences in the composition of plant assemblages between the two seasons (W vs S) and between surveys within each season for all a posteriori comparisons. Anthemis arvensis, Lolium rigidum, Festuca ligustica and Medicago polymorpha were the main discriminating plant species between seasons. Considering the discriminant species between the four winter surveys, we found a positive effect of August rain on Cynodon dactylonCSP and a negative one on Trifolium subterraneumCSP. Considering the spring surveys, we found a positive effect of January rain on L. rigidum and a negative effect on Plantago lanceolata. The rain affected the inter-annual dynamics of floristic composition in the Mediterranean grasslands. Other factors, such as temperature, remain to be investigated. Moreover, a more extended data series may allow us to strengthen our results.

Tall Herb Fringe Vegetation on Banks of Montenegrin Rivers as a Habitat Type of European Importance

River valleys are known to be of high natural value; however, they are exposed to a strong human influence. Anthropogenic changes are evident in the structure and species composition of plant assemblages; therefore, vegetation is a very good indicator of the state of the environment. Convolvuletalia sepium tall herb communities are a natural component of riverside vegetation; they are protected in the EU (habitat 6430), yet have been very poorly studied, especially in SE Europe. Information regarding the geographical distribution of these communities, and their floristic composition and threats, along with effective conservation and restoration strategies, remains insufficient; therefore, this study was aimed at a comprehensive investigation of tall herbs. The paper presents results of the first detailed study of this group of communities in Montenegro. Classification of 70 vegetation samples (relevés) using the UPGMA produced six clusters corresponding to plant communities which were included in the Dorycnio recti-Rumicion conglomerati. Two of them were ranked as associations: Mentho longifolii-Pulicarietum dysentericae and Rubo sancti-Eupatorietum cannabini, the latter new to science. Others (communities of Rubus caesius, Rubus caesius-Eupatorium cannabinum, Helianthus ×laetiflorus, and Helianthus tuberosus) were left without a syntaxonomic rank. The ordination analysis with the CANOCO software confirmed the authors’ hypothesis that the variability of the vegetation patches studied was related to the land use type and river size. Relevés taken in watercourses flowing through built-up areas were dominated by invasive alien species (IAS). Vegetation samples taken in heavily flooded areas, along the Zeta, one of the largest rivers surveyed, had a simplified species composition. Studies in Montenegro should be continued. Moreover, comparative studies of the Convolvuletalia sepium communities described in the Mediterranean region are also necessary. Attention is drawn to the overly narrow interpretation of habitat 6430 in the lowlands, as it lacks a representation of Mediterranean tall herbs.

Planting design influences green infrastructure performance: Plant species identity and complementarity in rain gardens.

Green infrastructure's capacity to mitigate urban environmental problems, like heat island effects and excessive stormwater runoff, is partially governed by its plant community. Traditionally, green infrastructure design has focused on engineered aspects, such as substrate and drainage, rather than on the properties of its living components. Since the functioning of these plant assemblages is controlled by ecophysiological processes that differ by species, the identity and relative abundance of the species used will influence green infrastructure performance. We used trait-based modeling to derive principles for the effective composition of green infrastructure plant assemblages, parameterizing our model using the vegetation and ecophysiological traits of the species within New York City rain gardens. Focusing on two plant traits that influence rain garden performance, leaf surface temperature and stomatal conductance, we simulated the cumulative temperature and transpiration for plant communities of differing species composition and diversity. The outcomes of the model demonstrate that plant species composition, species identity, selection effects, and interspecific complementarity increase green infrastructure performance in much the way biodiversity affects ecosystem functioning in natural systems. More diverse assemblages resulted in more consistent transpiration and surface temperatures, with the former showing a positive, saturating curve as diversity increased. While the dominant factors governing individual species leaf temperature were abiotic, transpiration was more influential at the community level, suggesting that plants within diverse communities may be cooler in aggregate than any individual species on its own. This implies green infrastructure should employ a variety of vegetation; particularly plants with different statures and physical attributes, such as low-growing ground covers, erect herbaceous perennials, and shrubs.

Pervasive impacts of climate change on the woodiness and ecological generalism of dry forest plant assemblages

Abstract Climate emergency is a significant threat to biodiversity in the 21st century, but species will not be equally affected. In summing up the responses of different species at the local scale, we can assess changes in the species quantity and composition of biotic assemblages. We used more than 420K curated occurrence records of 3060 plant species to model current and future patterns of plant species distribution in one of the world's largest tropical dry forests—the Caatinga. While allowing different model extrapolation scenarios, we estimated potential changes in the species richness and composition of dryland plant assemblages in response to projected climate change, and assessed how the ecological generalism and woodiness of plant assemblages can be impacted by the climate crisis. More than 99% of plant assemblages were projected to lose species by 2060, with biotic homogenisation—the decrease in spatial beta diversity—forecasted in 40% of the Caatinga. The replacement of narrow‐range woody species by wide‐range non‐woody ones should impact at least 90% of Caatinga plant assemblages. The exacerbated species loss in the dryland plant assemblages was connected to the heterogenisation and homogenisation of biotic assemblages. Still, the magnitude of climate change impacts on ecological generalism and woodiness patterns of dryland plant assemblages differ according to the direction of the biotic change process. Synthesis. The future increase in aridity will change the patterns of woodiness and ecological generalism of tropical dry forest plant assemblages by decreasing vegetation diversity and complexity. The projected biotic changes in dryland plant assemblages indicate the erosion of ecosystem services linked to biomass productivity and carbon storage. We highlight the importance of long‐term conservation planning for maintaining tropical dry forests.

Dinosaur extinctions related to the Jenkyns Event (early Toarcian, Jurassic)

The early Toarcian Jenkyns Event (~183 Ma) was characterized by a perturbation of the global carbon cycle, global warming, which at continental areas led to intensified chemical weathering, enhanced soils erosion, and intensified wildfires. Warming and acid rain affected diversity and composition of land plant assemblages, caused a loss of forests and thereby impacted on trophic webs. The Jenkyns Event, triggered by volcanic activity of the Karoo-Ferrar Large Igneous Province, changed terrestrial ecosystems, and also affected the dinosaurs. Fossil macroplant assemblages and palynological data reveal reductions in the diversity and richness of plant communities. A substantial loss of land plant biomass and a shift to forests dominated by Cheiropelidiaceae conifers occurred as a consequence of seasonally dry and warm conditions. Major changes occurred to hervivore dinosaurs, with extinction of diverse basal families of Sauropodomorpha (‘prosauropods’) as well as some basal sauropods. Ornithischian dinosaurs show patchy records; some heterodontosaurids disappeared and the scelidosaurids (Thyreophora) went extinct during the Jenkyns Event. The dominant carnivorous dinosaurs, the Coelophysoidea (Theropoda), died out during the Jenkyns Event. We interpret the Jenkyns Event as a terrestrial crisis for ecosystems, marked especially by floral changes and the extinction of some dinosaur clades, both hervivores and carnivores.

Breeding-bird assemblages of calcareous grasslands and heathlands provide evidence for Common juniper (Juniperus communis) as a keystone species

Relative to their biomass or abundance, keystone species have a disproportionate effect on many other organisms. Common juniper (Juniperus communis) is an evergreen shrub that has significant impacts on microclimate, composition of plant assemblages and herbivorous insects. However, J. communis is currently not considered a keystone species. The present study aims to provide deeper insights into the potential importance of juniper as a keystone species in its two main habitats: calcareous grasslands and heathlands. The response of breeding birds to the occurrence of Common juniper was highly similar in both habitat types. Plots with the presence of J. communis had a higher species richness and density of all and shrub-nesting species than absence plots. Additionally, presence plots exhibited a higher density (calcareous grasslands) or richness (heathlands) of threatened species than absence plots. Overall, the occurrence of scattered juniper shrubs boosted species richness and abundance of breeding birds. Responsible for this pattern were (i) the general increase in structural complexity and (ii) two (genuine) properties of the tall, evergreen shrub in particular: dense growth and prickly leaves. Due to the latter, the shrubs provide nesting sites that are strongly sheltered against predation and adverse weather. However, juniper shrubs have also an important function as song posts and perches for hunting. Additionally, the usually scattered distribution of juniper shrubs ensures a maximum territory density in calcareous grasslands and heathlands. Our study provides evidence that J. communis should be considered a keystone species in both habitat types of European conservation concern.

Large herbivores trigger spatiotemporal changes in forest plant diversity.

Large herbivores can exert top-down control on terrestrial plant communities, but the magnitude, direction, and scale dependency of their impacts remain equivocal, especially in temperate and boreal forests, where multiple disturbances often interact. Using a unique, long-term, and replicated landscape experiment, we assessed the influence of a high density of white-tailed deer (Odocoileus virginianus) on the spatiotemporal dynamics of diversity, composition, and successional trajectories of understorey plant assemblages in recently logged boreal forests. This experiment provided a rare opportunity to test whether deer herbivory represents a direct filter on plant communities or if it mainly acts to suppress dominant plants, which, in turn, release other plant species from strong negative plant-plant interactions. These two hypotheses make different predictions about changes in community composition and alpha and beta diversity in different vegetation layers and at different spatial scales. Our results showed that deer had strong effects on plant community composition and successional trajectories, but the resulting impacts on plant alpha and beta diversity patterns were markedly scale dependent in both time and space. Responses of tree and non-tree vegetation layers were strongly asymmetric. Deer acted both as a direct filter and as a suppressor of dominant plant species during early forest succession, but the magnitude of both processes was specific to tree and non-tree vegetation layers. Although our data supported the ungulate-driven homogenization hypothesis, compositional shifts and changes of alpha diversity were poor predictors of beta diversity loss. Our findings underscore the importance of long-term studies in revealing nonlinear temporal community trends, and they challenge managers to prioritize particular community properties and scales of interest, given contrasting trends of composition and alpha and beta diversity across spatial scales.

Climate and land‐use drive the functional composition of vascular plant assemblages across Norway

Traditionally, biogeography has described the distribution of species. But as plant functional traits and functional diversity underpin ecosystem dynamics, understanding drivers of functional diversity at biogeographical scales is essential to understand spatial variation in ecosystem characteristics, particularly in light of ongoing environmental changes. Here we investigate geographic patterns of functional diversity and ‐traits of the Norwegian flora. We explore whether climate, land‐use or glacial history are important drivers of functional diversity. We combine species occurrence records and assemblage‐means of functional traits to assess the spatial distribution of functional traits and ‐diversity of native vascular plants in Norway in a 20 × 20 km grid. We use multiple‐model inference to identify which environmental factors contribute the most in explaining the spatial patterns of trait distributions and functional diversity. Additionally, we use the constructed models to predict potential changes in distributions of traits and functional diversity given different climate change scenarios.Both individual traits and functional diversity display clear geographic patterns, predictable by climate, landscape and glacial history. Traits related to plant size and growth peak in warmer areas and are predicted to increase in the future, as is functional richness and dispersion. In contrast, functional evenness peaks in northern regions and is predicted to decrease in the future.The different environmental drivers vary in degree of importance, effect sizes and ‐directions on the assemblage‐averaged functional traits and ‐diversity. This underlines the importance of multiple drivers in determining plant assemblage functionality. In the face of climate‐ and land‐use change, Norway is expected to become warmer, wetter and experience a substantial increase in anthropogenic land‐uses, such as increased urbanisation. In turn, the functional composition of the Norwegian flora is predicted to shift towards tall, woody, fast‐growing species.

Phylogenetic relatedness of food plants reveals highest insect herbivore specialization at intermediate temperatures along a broad climatic gradient.

The composition and richness of herbivore and plant assemblages change along climatic gradients, but knowledge about associated shifts in specialization is scarce and lacks controlling for the abundance and phylogeny of interaction partners. Thus, we aimed to test whether the specialization of phytophagous insects in insect-plant interaction networks decreases toward cold habitats as predicted by the 'altitude niche-breadth hypothesis' to forecast possible consequences of interaction rewiring under climate change. We used a non-invasive, standardized metabarcoding approach to reconstruct dietary relationships of Orthoptera species as a major insect herbivore taxon along a broad temperature gradient (~12°C) in Southern Germany. Based on Orthoptera surveys, feeding observations, collection of fecal pellets from >3,000 individuals of 54species, and parallel vegetation surveys on 41grassland sites, we quantified plant resource availability and its use by herbivores. Herbivore assemblages were richer in species and individuals at sites with high summer temperatures, while plant richness peaked at intermediate temperatures. Corresponding interaction networks were most specialized in warm habitats. Considering phylogenetic relationships of plant resources, however, the specialization pattern was not linear but peaked at intermediate temperatures, mediated by herbivores feeding on a narrow range of phylogenetically related resources. Our study provides empirical evidence of resource specialization of insect herbivores along a climatic gradient, demonstrating that resource phylogeny, availability, and temperature interactively shape the specialization of herbivore assemblages. Instead of low specialization levels only in cold, harsh habitats, our results suggest increased generalist feeding due to intraspecific changes and compositional differences at both ends of the microclimatic gradient. We conclude that this nonlinear change of phylogeny-based resource specialization questions predictions derived from the 'altitude-niche breadth hypothesis' and highlights the currently limited understanding of how plant-herbivore interactions will change under future climatic conditions.

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

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

Patterns and drivers of phylogenetic structure of pteridophytes in China

AbstractAimPrevious studies have found strikingly different geographical patterns of phylogenetic diversity of gymnosperms and angiosperms, which have been suggested to result, in part, from the greater age of the former. To assess the effects of clade age on phylogenetic structure, we assessed phylodiversity patterns of pteridophytes (lycophytes and ferns), which combine ancient and modern lineages, across China.LocationChina.Time periodPresent day.TaxonPteridophytes.MethodsWe divided China into 66 regions and collated species lists of pteridophytes for each region. We then related taxonomic and phylogenetic diversity, and their related metrics, to six climatic variables for pteridophytes as a whole and for different evolutionary clades. We examined the effect of spatial autocorrelation among regional floras on the results.ResultsWe found that when all pteridophytes or ferns were considered, the patterns resembled those of gymnosperms, presumably reflecting the effects of several ancient global mass extinctions and the relict distribution of old families. In contrast, when we considered only the modern Polypodiales radiation, which accounts for three‐quarters of current fern diversity and is about as old as the angiosperm radiation, we found a pattern similar to that of angiosperms. This pattern is consistent with the tropical niche conservatism hypothesis and suggests that both major groups of land plants have a broadly similar evolutionary trajectory, with most families originating in tropical conditions and few families adapting to cold and arid conditions.Main conclusionsOur study shows that the phylogenetic structures of more recently evolved and diversified clades of pteridophytes are fairly consistent with the tropical niche conservatism hypothesis, suggesting that the age of the taxon, its physiological adaptations and the global climatic changes that it experienced during its evolutionary history are reflected in the composition of current plant assemblages.

Phylogenetic conservatism of fruit development time in Chinese angiosperms and the phylogenetic and climatic correlates

QuestionsDocumenting the patterns and drivers of functional trait distributions at large spatial scales is key to our fundamental understanding of the composition of plant assemblages. However, phylogeographic patterns of fruit development time (FDT, the difference between flowering and fruiting dates) have remained unstudied. Here we compiled reproductive phenology (flowering and fruiting time) and species distribution data for 6838 angiosperm species in China to explore whether FDT is more phylogenetically conserved as latitude and elevation increase, whether the phylogenetic signal of FDT correlates with phylogenetic structure and potential climatic drivers across China, and whether the environmental determinants of phylogenetic signal of FDT differ between herbaceous and woody species. LocationChina MethodsWe divided China into 268 200 × 200 km grid cells and calculated the phylogenetic signals of FDT in each grid cell using pagel’s λ. We then regressed the phylogenetic signals of FDT as a function of either latitude or elevation, individually. We examined the relationship between phylogenetic signals of FDT and climate variables using both ordinary and spatial linear regressions. We also examined the relationship between the phylogenetic signal of FDT and either net relatedness index (NRI) or clade age of each grid-cell. ResultsWe found that phylogenetic signals in FDT increased as elevation and latitude increased. The Pagel’s λ of FDT was negatively correlated with clade age but positively correlated with NRI. Precipitation in the wettest quarter was the primary variable affecting the phylogenetic signal for herbaceous species, while minimum temperature of the coldest month and temperature seasonality were the two most important climatic factors for woody species. ConclusionsStrength of phylogenetic conservatism of FDT is greater at higher latitudes and elevations. The latitudinal and elevational patterns, where mean clade age of species lowers as temperature decreases, and angiosperm assemblages tend to be more phylogenetically clustered at higher elevations and higher latitudes, could be explained by the Tropical Niche Conservatism hypothesis. The phylogenetic signals of herbs and of woody plants are triggered by different climatic drivers. Our findings have important implications for the study of large-scale geographical gradients in plant species richness, phylogenetic diversity and community assembly.

Modern pollen rain predicts shifts in plant trait composition but not plant diversity along the Andes–Amazon elevational gradient

AbstractAimsTerrestrial ecosystems are changing in biodiversity, species composition and functional trait composition. To understand the underlying causes of these changes and predict the long‐term resilience of the ecosystem to withstand future disturbances, we can evaluate changes in diversity and composition from fossil pollen records. Although diversity can be well estimated from pollen in temperate ecosystems, this is less clear for the hyperdiverse tropics. Moreover, it remains unknown whether functional composition of plant assemblages can be accurately predicted from pollen assemblage composition. Here, we evaluate how community‐weighted mean (CWM) traits and diversity indices change along elevation.LocationAmazon–Andes elevation gradient in Peru.MethodsWe used 82 modern pollen samples and 59 vegetation plots along the elevation gradient, and calculated CWM traits and diversity indices for each pollen sample and vegetation plot. We also quantified the degree to which taxa are over‐ or underrepresented by their pollen, by dividing the relative pollen abundance by the relative basal area abundance in the nearby vegetation survey plots (i.e. the R‐rel values).ResultsWe found that CWM wood density increased, and CWM adult height and leaf area decreased with elevation. This change was well predicted by pollen assemblages, indicating that CWM trait–environment relationships based on pollen abundance data provide meaningful results. Diversity (richness, Shannon and Simpson) decreased with elevation for vegetation plots, but these trends could not be observed from pollen assemblages.ConclusionsOur results demonstrate that more research is needed to develop methods that lead to accurate diversity estimates from pollen data in these tropical ecosystems, but that CWM traits can be calculated from pollen data to assess spatial shifts in functional composition. This opens opportunities to calculate CWM traits from fossil pollen data sets in the tropics, with broad implications for improving our understanding and predictions of forest dynamics, functioning and resilience through time.

Land use history drives differences in functional composition and losses in functional diversity and stability of Neotropical urban forests

With urbanisation rapidly transforming our world, a better understanding of how urban ecosystems can contribute to biodiversity conservation is urgently needed. Here, we investigated the functional composition and diversity of plant assemblages in different types of urban forests with the intent to predict the stability of the functions provided by these forests through the functional redundancy and response diversity of species. For this, we used data from non-urban mature forests, remnant urban forests, urban forests regenerated from croplands and urban forests regenerated from soil denudation, all located in the Brazilian Atlantic Forest. Our results showed that species functional composition shifted among urban and non-urban forests. However, functional diversity was lost only in urban forests with some previous use, indicating that the natural regeneration of urban forests after previous land use results in functionally poor forests. Urban forests regenerated from soil denudation (more intense disturbance) had a lower functional diversity. Conversely, urban forests regenerated from cropland (less intense disturbance) showed only a reduction in the number of functions provided. Our analysis also revealed the reduced functional redundancy and response diversity of urban forests with previous land use, which may indicate a greater vulnerability of the functions provided by these forests. Thus, we emphasise in this study the importance of land use history for decision making in urban forest conservation policies and highlight the crucial role of natural remnant urban forests as reservoirs of functional diversity and stability in highly degraded and fragmented landscapes.

Functional diversity and composition of Caatinga woody flora are negatively impacted by chronic anthropogenic disturbance

Abstract Tropical plant assemblages can be taxonomically and phylogenetically impoverished by chronic anthropogenic disturbance (CAD), such as firewood collection and extensive grazing. However, to what extent the functional dimension responds to CAD is still unclear. Such knowledge is urgently required for predicting, preventing or even reversing the impacts of CAD. Chronic anthropogenic disturbance may operate as an ecological filter by selecting functional trait values (e.g. low wood density), thereby altering the functional composition and diversity of plant assemblages. We tested this hypothesis using 29 woody plant assemblages across three ontogenetic stages (seedlings, saplings and adults) in a 220‐km2 landscape of the Caatinga, northeast Brazil. We adopted a CAD index consisting of four indicators (proximity to urban centre and houses and the density of both people and livestock) and tested how well it explained the functional diversity and effect sizes (richness, evenness and dispersion) and composition (community‐weighted mean). Chronic anthropogenic disturbance affected several functional metrics across the three ontogenetic stages. However, CAD effects were stronger in adult communities by negatively affecting functional richness, dispersion and their effect sizes. CAD also altered the functional composition of leaf mass per area, woody density and leaf area of adult assemblages. Sapling communities were affected in terms of functional composition (leaf area, leaf dry matter and wood density), with positive and negative effects, while seedling assemblages responded positively to CAD only in terms of functional evenness and its effect size. Some changes in functional metrics were influenced by dominant Euphorbiaceae species across ontogenetic stages, especially in terms of leaf area and woody density. Synthesis. Chronic anthropogenic disturbance is an important driver of plant‐community functional organization across ontogenetic stages in the Caatinga. Adult assemblages are particularly sensitive and tend to lose functional niche space and support more acquisitive rather than conservative strategies as chronic anthropogenic disturbance increases. The proliferation of Euphorbiaceae disturbance‐adapted species can explain part of the community responses to chronic anthropogenic disturbance. Our findings highlight the ecological effects of chronic anthropogenic disturbance and show that it is a key influence on tropical biotas. Changes in plant functional traits associated with plant resource use are likely to affect ecosystem functioning and services provided by Caatinga.

Herbivory and dropping effects by small mammals on salt‐marsh vegetation vary across microhabitats

AbstractQuestionDoes the effect of droppings and herbivory by wild guinea pigs on salt‐marsh vegetation vary across microhabitats?LocationUpper salt marsh in the Mar Chiquita coastal lagoon (37°44′52″ S, 57°26′6″ W, Argentina).MethodsDuring autumn 2014, we performed a micro‐scale experiment manipulating droppings of wild guinea pigs (Cavia aperea). After 15 days, we compared the content of nutrients (i.e., NH4+, NO3−, and PO43−) in soil. Then, we started two factorial experiments in the high marsh, specifically one in marsh matrix (i.e., tall vegetation) and the other in open patches (i.e., short vegetation). Units were randomly assigned to different treatments (with and without herbivores and droppings). In early summer, we compared total plant cover, maximum height, above‐ground biomass, plant species richness and the composition of plant assemblages between treatments.ResultsDroppings increased the content of PO43− in soil by five times, but decreased the content of NO3−. Herbivory reduced total cover, plant height, and above‐ground biomass in the marsh matrix and the open patches. In the marsh matrix, droppings increased the total cover, whereas herbivory reduced the abundance of Spartina densiflora (cover and above‐ground biomass) and subordinate species (cover). Additionally, the cover of subordinate species was negatively associated with the cover of Spartina densiflora. Therefore, in the marsh matrix, by increasing light availability at the ground level, herbivory increased plant species richness, but with low cover of subordinate species. In contrast, in open patches, herbivory and droppings interacted to reduce plant species richness.ConclusionHerbivory by small mammals can control the above‐ground biomass, structure, and plant community composition of the high marsh, but non‐trophic mechanisms (droppings) can also affect community composition. Nonetheless, ecological impacts of small mammals depend on the context, because the magnitude and direction of trophic (herbivory) and non‐trophic (droppings) effects change across microhabitats.

Plant Colonization of Green Roofs Is Affected by Composition of Established Native Plant Communities

Human activities associated with urbanization have negatively affected the biodiversity of native plant communities globally. Establishing native species assemblages on green roofs may help conserve native plant diversity in urban areas, but these assemblages are susceptible to colonization by species from the surrounding landscape. In natural communities, colonization from the regional species pool reflects the filtering effects of both abiotic and biotic factors, but the relative effects of these factors on green roof colonization are not well understood. To address this knowledge gap, we studied colonization dynamics of 10 green roofs in New York City (NY, USA), each with 12 split-plots planted with an erect C4 graminoid dominant (Hempstead Plains: HP) and a tuft C3 graminoid and forb dominant (Rocky Summit: RS) species assemblage derived from native communities. Six of the 12 plots contained shallow growing medium, while the other six contained deeper growing medium. Resident plants were planted in May 2010. Fifty-eight non-resident plant species colonized plots between August 2011 and August 2012, with two native and 10 non-native species accounting for 90% of total colonist dry mass. Colonist dry mass and richness decreased with increasing resident plant cover, but the effects of growing medium depth on colonist dry mass and richness differed between assemblages. Forbs accounted for 81% of the colonist dry mass from the HP assemblage, but just 31% in the RS assemblage. Further, forbs accounted for over 95% of colonist dry mass in June and July, while graminoids accounted for over 95% of colonist dry mass in August. These results indicate colonization of planted green roofs may be strongly affected by the composition of established plant assemblages and that these effects may vary temporally, even within a single growing season. Further, the inconsistent effects of growing medium depth suggest that niche overlap and complementarity in rhizosphere dynamics may influence colonization more in some systems compared with others. Additional research is required to describe the effects of colonist management strategies, as well as the roles of priority effects, niche complementarity and community assembly, on long-term dynamics of colonization on green roofs planted with native plants.

Spontaneous revegetation of a peatland in Manitoba after peat extraction: diversity of plant assemblages and restoration perspectives

There are very few studies on the spontaneous revegetation of cutover fens or bogs from which peat has been extracted to the minerotrophic layers. Most peatlands with fen-type residual peat have problems regenerating a plant cover satisfactorily from a restoration point of view. We nevertheless found a site (Moss Spur, Manitoba, Canada) presenting a substantial and diversified spontaneous plant cover. We estimated that the site would provide insights about natural revegetation processes operating in peatlands. Vegetation assemblages and environmental conditions were surveyed 19 years after extraction activities ceased. Moss Spur has densely revegetated (163 plant species, vegetation cover of 94%) with minimal human assistance. However, the composition of plant assemblages varies considerably across the site, depending on certain abiotic variables, particularly water pH, water table level, and the thickness of the residual peat layer. Moss Spur was remarkably wet considering the past peat extraction activities and the absence of active rewetting procedures. The high water table level may in part explain the successful revegetation. However, plant assemblages were not of equal quality from a restoration perspective. Some assemblages were highly diversified, and especially those dominated by Scirpus cyperinus, a species that should be further considered in peatland restoration projects to direct the recovery of the peatland towards a natural fen species composition.

A comparison of biotic groups as dry-phase indicators of ecological quality in intermittent rivers and ephemeral streams

Intermittent rivers and ephemeral streams (IRES) are dynamic ecosystems that shift between aquatic and terrestrial states. IRES are widespread, abundant and increasing in extent, but developing biomonitoring programmes to determine their ecological quality is challenging. To date, quality assessments have focused on the aquatic organisms present during wet phases, whereas dry-phase communities remain poorly characterized. We examined multiple biotic groups present in dry IRES channels, to compare assemblages at sites impacted and unimpacted by human activity and to evaluate the potential of each group as an ecological quality indicator. We explored existing, unpublished data for three biotic groups: an aquatic microflora (diatoms), an aquatic fauna (the invertebrate ‘seedbank’), and a mixed flora (aquatic and terrestrial plants); notably, we did not source data for terrestrial assemblages with high potential to act as indicators. Diatom and plant assemblage composition differed between impacted and unimpacted sites, and the latter assemblages were more diverse and included more indicator taxa. Invertebrate seedbank taxa richness was higher at unimpacted sites but compositional differences were not detected, probably due to the coarse taxonomic resolution to which abundant taxa were identified. Performance of standard indices of ecological quality was variable, but differences were identified between impacted and unimpacted conditions for all biotic groups. Our results can inform the enhancement of biomonitoring programmes designed to characterize IRES ecological quality in relation to legislative targets. We highlight the need to integrate wet- and dry-phase survey data in holistic quality assessments. Although we suggest diatoms, aquatic plants and the aquatic invertebrate seedbank as having the potential to inform assessment of dry-phase ecological quality, we highlight the need for research to further characterize these aquatic groups and, crucially, to explore terrestrial assemblages with high potential to act as dry-phase quality indicators.

Late Quaternary Environments of the Teton Mountains, Wyoming: A Pollen Record from Green Lake

Late Quaternary forest succession in Wyoming’s Rocky Mountains, occurred in random patterns, because it reflects differences between the Glacial vegetation at lower elevations on the east vs. the west of the Rockies, as well as along the mountain crest to the south. Differential melting of mountain glaciers resulted in differences in the timing of recolonization. Significant variations in the composition of plant assemblages occurred due to delays in species’ arrival, and even in the exclusion of species. Holocene climate variability, especially ongoing global warming, added to the complex dynamics of plant assemblages with warm climate species replacing early Holocene, cooler climate species. The pollen record from Green Lake (located in a glacial cirque on the west side of the Teton Mountains in Teton County, Wyoming) addresses the local vegetation response from just before the fall of Mazama ash to the end of the middle Holocene warm period. Although the earlier portion of the pollen sequence records some of the last adjustments as some plant species were still arriving after de-glaciation, by the time Mazama ash fell it was climate variation that determined most of the dynamics observed in the Green Lake record. The results reveal a sequence of wetter and drier periods based upon the presence of diagnostic tree species.  A moist late early Holocene was followed by a dry middle Holocene, which ended about 6,400 cal. B.P., and was followed between 5,000 to 2,800 cal. B.P. by a sequence of drier and moister climate episodes.