Shifts In Plant Communities Research Articles

Nitrogen and phosphorus fertilization consistently favor pathogenic over mutualistic fungi in grassland soils

Ecosystems across the globe receive elevated inputs of nutrients, but the consequences of this for soil fungal guilds that mediate key ecosystem functions remain unclear. We find that nitrogen and phosphorus addition to 25 grasslands distributed across four continents promotes the relative abundance of fungal pathogens, suppresses mutualists, but does not affect saprotrophs. Structural equation models suggest that responses are often indirect and primarily mediated by nutrient-induced shifts in plant communities. Nutrient addition also reduces co-occurrences within and among fungal guilds, which could have important consequences for belowground interactions. Focusing only on plots that received no nutrient addition, soil properties influence pathogen abundance globally, whereas plant community characteristics influence mutualists, and climate influence saprotrophs. We show consistent, guild-level responses that enhance our ability to predict shifts in soil function related to anthropogenic eutrophication, which can have longer-term consequences for plant communities.

The influence of roots on mycorrhizal fungi, saprotrophic microbes and carbon dynamics in a low‐phosphorus Eucalyptus forest under elevated CO2

Abstract Elevated atmospheric carbon dioxide (eCO2) can impact soil organic matter (SOM) dynamics by changing the rates of carbon (C) losses and gains. In the rhizosphere, these changes are usually assumed to be the result of root‐mediated eCO2 impacts on saprotrophic microbes via altered below‐ground C allocation. This C allocation can also impact mycorrhizal fungi and their role in SOM dynamics. However, direct field quantifications of the influence of roots on both mycorrhizal fungi and saprotrophs together with SOM dynamics in forests exposed to eCO2 are rare. This is especially true in phosphorus (P)‐limited systems, even though ecosystem responses to eCO2 are known to depend on P availability. We assessed root mediation of eCO2 impacts on saprotrophs, mycorrhizal fungi, and C dynamics of root litter and mineral soil C (SOM‐C) in a mature, P‐limited Eucalyptus woodland exposed to eCO2. We used a novel nested‐mesh‐bag method to manipulate roots access to the substrates in a 1‐year field incubation. We used an isotopic approach to trace C dynamics and performed a comprehensive microbial community analysis, along with nutrients and enzymatic activity measurements. Roots increased microbial biomass, fungal:bacterial ratio, plant‐derived C gains and substrate C losses while decreasing P availability and specific enzymatic activity. eCO2 increased bacterial relative abundance in root litter and protozoa in SOM‐C, but it did not enhance root impacts or mycorrhizal fungi biomass. Our combination of in‐situ approaches allowed us to demonstrate that while roots have multiple impacts on soil microbial communities and C dynamics, they are not the main drivers of responses to eCO2 in this P‐limited forest. Other factors beyond enhanced root‐derived below‐ground C inputs such as seasonality of nutrient and water availability, and shifts in plant communities may be more important in modulating eCO2 impacts on soil dynamics in P‐limited systems. ​A free Plain Language Summary can be found within the Supporting Information of this article.

Revegetation significantly increased the bacterial-fungal interactions in different successional stages of alpine grasslands on the Qinghai-Tibetan Plateau

Numerous restoration measures have been implemented to rebuild degraded alpine grasslands on the Qinghai-Tibetan Plateau, one of the most fragile regions in the world. Understanding the responses of soil microbes to restoration activities is critical to predict restoration direction and trajectories, as soil microbes play a key role in ecosystem functioning and nutrients cycling. In this study, we identified the effects of revegetation on soil microbial community composition and diversity, and the interaction between bacterial and fungal taxa in different successional stages (early stage, middle stage, late stage) by using a severely degraded grassland as the baseline, and healthy grassland as the target. Our results show that the composition of bacteria at phylum level and fungi at class level were significantly changed between successional stages. The diversity of bacteria at OTU level was significantly decreased, while the diversity of fungal OTUs were not significantly changed with successional stages. Plant and soil properties explained 53.15% variation of bacterial structure and 46.16% variation of fungal structure. Plant community, soil organic carbon, total nitrogen, and soil pH mainly influence microbial community during recovery process. Bacterial and fungal groups would become more similar to that of the healthy grassland along successional stages, because of the shift in soil resources and plant community. Total links and negative links of bacteria-fungi interaction networks increased along successional stages of revegetated grasslands. Keystone species in each network also changed with successional stages. These findings verified that revegetation could be effective to restore the microbial community of severely degraded grassland on the Qinghai-Tibetan Plateau.

HYDRAULICS OF PINUS (SUBSECTION PONDEROSAE) POPULATIONS ACROSS AN ELEVATION GRADIENT IN THE SANTA CATALINA MOUNTAINS OF SOUTHERN ARIZONA

The ability of plants to tolerate and recover from periodic water stress affects their competitive ability, survival, and distribution, leading to shifts in plant communities as environmental conditions change. We investigated the hydraulic traits of two closely related Pinus taxa to assess population and taxonomic variability in plant hydraulic traits. We hypothesized that traits would vary with elevation but exhibit similar traits where taxa co-occurred. We measured predawn and midday leaf pressure potential (Ψp) across three seasons, xylem specific hydraulic conductivity (Ks), and vulnerability to xylem embolism (P50). These were measured on Pinus ponderosa var. brachyptera (Engelm.) Lemmon that occurred at a high elevation site (2770 m), P. arizonica Engelm. at a low elevation site (2135 m), and both species where they co-occurred at the mid-elevation site (2475 m) in the Santa Catalina Mountains of southern Arizona. Plants from the high elevation site had the least negative Ψp and the highest Ks. The two taxa differed from one another when compared between the high and low elevation sites, but they were not different where they co-occurred. The two Pinus taxa show plasticity in their hydraulic traits across sites. Conditions across the elevational gradient appear to lead to a convergent solution in hydraulic traits for these taxa where their ranges overlap but differences in traits where they do not overlap. Increasing aridity in the region could lead to shifts in suitable habitat, reduced water transport ability at range margins, and shifts in population distributions.

When do grasses resprout after fire?

This article is a Commentary on Simpson et al. (2021), 230: 832–844.

Improved simulation of plant-animal interactions in African savannas with the extended land use change model LUCIA

Process-based modelling is needed to assess potential ecological impacts of large-scale intensification of African savanna rangelands and to investigate major processes involved, that cannot be tested on appropriate temporal and spatial scales at field level. To date, modelling conversion or integration of crop- and pasture-based systems in savanna ecosystems is not possible at the necessary level of detail. The Land Use Change Impact Assessment tool (LUCIA) dynamically simulates spatially explicit impacts of land-use change on ecosystem functions within a grid-based landscape. We added a physiologically detailed source-sink plant growth module with growth reserves, dynamic biomass partitioning, and dormancy to LUCIA to simulate a grazed rangeland vegetation in Borana, Ethiopia. Grass and tree growth, validated against measured above-ground biomass time series were most sensitive to dormancy break or induction parameters that control the growing period under strong rainfall seasonality. A moderate stocking rate of cattle allowed pasture persistence and continuous fodder production. Overgrazing caused depletion of root and tree stem growth reserves that were needed for seasonal regrowth. Consequently, pasture degraded due to reduced regrowth capacity and reserve replenishment. Physiological processes are well represented, laying the foundation for integration of further ecological processes, such as tree recruitment, bush encroachment, and plant community shifts.

Rewiring of peatland plant–microbe networks outpaces species turnover

Enviro–climatic changes are thought to be causing alterations in ecosystem processes through shifts in plant and microbial communities; however, how links between plant and microbial communities change with enviro–climatic change is likely to be less straightforward but may be fundamental for many ecological processes. To address this, we assessed the composition of the plant community and the prokaryotic community – using amplicon‐based sequencing – of three European peatlands that were distinct in enviro–climatic conditions. Bipartite networks were used to construct site‐specific plant–prokaryote co‐occurrence networks. Our data show that between sites, plant and prokaryotic communities differ and that turnover in interactions between the communities was complex. Essentially, turnover in plant–microbial interactions is much faster than turnover in the respective communities. Our findings suggest that network rewiring does largely result from novel or different interactions between species common to all realised networks. Hence, turnover in network composition is largely driven by the establishment of new interactions between a core community of plants and microorganisms that are shared among all sites. Taken together our results indicate that plant–microbe associations are context dependent, and that changes in enviro–climatic conditions will likely lead to network rewiring. Integrating turnover in plant–microbe interactions into studies that assess the impact of enviro–climatic change on peatland ecosystems is essential to understand ecosystem dynamics and must be combined with studies on the impact of these changes on ecosystem processes.

How Does Mangrove Expansion Affect Structure and Function of Adjacent Seagrass Meadows?

Temperatures are increasing globally and causing species-specific geographic range expansions. In the Gulf of Mexico, mangroves are encroaching regions historically dominated by temperate salt marshes, changing animal communities and nutrient cycling in the intertidal zone. Marine systems are highly connected; therefore, we expect that changes in the intertidal will alter functions of adjacent subtidal seagrass meadows. We surveyed seagrass meadows adjacent to mangroves, salt marshes, and a mixture of the two and asked, do changes in intertidal plant composition influence (1) environmental conditions (subtidal water and sediment characteristics); (2) biogeochemical cycling (net oxygen and nitrogen gas fluxes); (3) seagrass meadow cover, biomass, and productivity; and (4) invertebrate community assemblage? There are clear differences in sediment organic matter and net nitrogen gas (N2) fluxes between adjacent intertidal habitats, but the magnitude or direction of change differs seasonally. We hypothesize that this seasonal pattern is due to outwelling from the intertidal, as mangroves senesce in fall, and marshes senesce later in winter. Therefore, changes in adjacent intertidal habitat can impact the timing of organic matter delivery. This also has implications for seagrass biomass. Thalassia testudinum belowground biomass adjacent to mangroves substantially decreased over the winter, suggesting vulnerability to stressors as the intertidal plant community shifts from marsh to mangrove dominance. Epifauna density and diversity did not vary among seagrass meadows based on adjacent intertidal habitats, but subtle differences in community assemblages associated with shifts in intertidal plant community were detected. This work demonstrates that impacts of species range expansions are far-reaching due to connectivity in marine systems.

Quantifying the relationship between soil seed bank and plant community assemblage in sites harboring the threatened Ivesia webberi in the western Great Basin Desert

AbstractQuestionsThe soil seed bank is an important ecosystem component that can be pivotal for long‐term persistence of many plant species, especially after disturbances followed by the invasion of alien weeds. However, many Great Basin Desert perennials produce relatively few viable seeds, while large areas of the Great Basin are currently invaded by alien weeds. This could result in dissimilarity in floristic composition between the above‐ground vegetative community and the soil seed bank, causing abrupt plant community shifts following disturbance. Therefore, we asked what is the relationship in the floristic composition between the above‐ground communities and the soil seed bank in sites where the threatened Ivesia webberi occurs?LocationThe Great Basin Desert, United States.MethodsWe used Dice–Sorensen's similarity index to estimate similarity between the standing vegetation and the soil seed bank. Redundancy analysis and variation partitioning were used to quantify the relationship between the total abundance of the sampled above‐ground flora and the soil seed bank, accounting for effects of spatial processes and environmental variables describing climate, soils, and vegetation in the 10 sites.ResultsFindings reveal high dissimilarity in species assemblage and abundance between the above‐ground plant communities and the soil seed bank. Most of the dominant native plant species sampled in the standing vegetation were absent in the soil seed bank, and the soil seed bank was dominated by invasive alien weeds.ConclusionsDivergence in the floristic composition between the above‐ground communities and the soil seed bank in Ivesia webberi habitat indicates low resilience and high risk of native species loss following perturbation. Post‐disturbance succession in these plant communities may be largely dominated by invasive annual species; therefore, reduction of invasive species and native plant seeding may be necessary to sustain the ecological legacies of the desert ecosystem.

Interactive disturbances drive community composition, heterogeneity, and the niches of invasive exotic plant species during secondary succession

ABSTRACT Background Simultaneous disturbances during secondary succession can cause plant community shifts, facilitating exotic species invasions. However, it remains unclear if exotic invasion is facilitated by additive or interactive disturbance effects during succession. Aims Our aim was to investigate temporal shifts in plant species composition, invasive exotics, and indicator species during simultaneous disturbances in secondary succession. Methods We used species data from nine plant surveys over 22 years of a field experiment in an old field where parallel strips were randomly assigned to each of the 9 crossed fertiliser and mowing disturbance treatments. Multivariate and ordination analyses were used to quantify community response to disturbance. Indicator species analysis identified plants characteristic of different disturbance levels. Results Plant communities differed in composition and heterogeneity based on interactive effects of disturbance treatments whereas pairwise tests showed these differences occurred in over two-thirds of treatment combinations. Of the 44 indicator plant species, seven of the eight exotic species of concern for Illinois were indicator species and characterised particular disturbance treatments and surveys. Conclusions Changes in these successional plant communities depend on the interaction among disturbances, which can facilitate exotic plant invasions, leading to plant communities which disproportionately maintain invasive exotic plants as compared to other naturalised exotic and native plant species.

Changes in terrestrial ecosystems across the Cretaceous-Paleogene boundary in western Canada inferred from plant wax lipid distributions and isotopic measurements

Changes in terrestrial environments across the Cretaceous-Paleogene boundary, including plant ecology and carbon and water-cycling, remain poorly defined. Fluvial sediments spanning the Cretaceous-Paleogene (K-Pg) boundary of southern Saskatchewan, Canada contain well preserved plant wax n-alkanes that provide a means of reconstructing changes to plant ecology and carbon and water cycling during this mass extinction event. We measured n-alkane carbon (δ13C) and hydrogen (δ2H) isotope ratios in two sedimentary sections and applied established fractionation factors to estimate the isotopic compositions of precipitation and bulk sedimentary organic matter sources. We also analyzed the distribution of n-alkanes as an indicator of the relative abundance of aquatic and terrestrial plants. We find a consistent shift towards a greater relative abundance of longer-chain n-alkanes across the boundary, implying a persistent increase in the relative abundance of terrestrial plants in the sedimentary basin. This is consistent with an increase in birch and elm palynomorphs immediately above the boundary. We hypothesize the extinction of all large herbivores at the boundary may have facilitated this transition to a terrestrial angiosperm dominated flora immediately after the boundary. We also find that the region was characterized by isotopically light precipitation, with δ2H values between −95‰ to −160‰, but do not observe evidence for major millennial-scale changes in regional precipitation isotopic composition spanning the boundary. n-Alkanes derived from both aquatic and terrestrial plants at one site display an upward trend in δ13C values of approximately 2‰ across the K-Pg boundary. This suggests millennial-scale local or global carbon-cycle variability altering either plant carbon isotope fractionation or the carbon isotope composition of dissolved inorganic carbon and atmospheric CO2. Overall our results suggest that carbon and water cycle changes associated with the K-Pg impact in terrestrial environments in western Canada were short-lived, but ecological shifts in plant communities were longer-lasting.

Plant Community Shifts in Response to Fire and Bison in a Restored Tallgrass Prairie

To redress prairie loss, managers seed former agricultural lands and reinstate key ecosystem processes with prescribed fires and reintroduction of native grazers to create restored prairies. Bison (Bison bison) were almost hunted to extinction in the late 1800s but are recovering and have recently been reintroduced to restored prairies for their ecosystem engineering roles. The effects bison and fire have on remnant (never-plowed) prairie vegetation are well documented. However, there is little known about how bison will impact plant communities in restored prairies. These effects are most likely driven by reduction of competition from grasses and increased heterogeneity from disturbance. This study aimed to quantify bison impacts on vegetation in a chronosequence of restored prairie with varied burning regimes. We found that plant diversity decreased with restoration age and did not differ among either grazing or fire treatments. However, grazed sites displayed more variation within plant community composition. Older restorations tended to be more similar in species and functional group composition in comparison to younger sites. Although the roles of bison and fire were not as important in these first three years after reintroduction as predicted, changes in composition suggest that bison effects may become more apparent in later years as grazing drives different compositional trajectories.

Plant Community Response to Hydrologic Restoration in the Great Dismal Swamp

Peatlands in the mid-Atlantic outer coastal plain region contain obligate hydrophyte species which were harvested and replaced by facultative tree species. The Great Dismal Swamp was drained from the colonial era until 1974, when water levels were partially restored. In September 2013, further restoration consisting of two large weirs followed extensive peat-burning fires. This study evaluated depth-to-water-table and vegetation structure both prior to and following weir operation. Wells were installed and depth-to-water-table was recorded continuously from 2013 to 2015 within six of the 15 forested stands where vegetation species dominance was quantified for tree, shrub, herb, and vine strata. Following weir installation in 2013, water tables rose an average of 28.08 cm in 2014 and 32.69 cm in 2015, during the June–July peak of the growing season. Most water levels were too low to meet the federal regulatory indicator of wetland hydrology or the seasonally flooded, saturated hydrologic regime typical of peatlands. After restoration, species dominance and frequency, as well as metrics based on hydrophyte dominance and floristic quality in study plots, were unchanged. Ordinations detected no directional shift in plant community composition among pre- and post-weir periods. Although insufficient time may have passed for shifts in plant communities, additional increases in water level above those reported here appear necessary to restore a pre-disturbance hydrologic regime and plant community structure. However, above some threshold water level, planted trees will exhibit increased mortality and limit reestablishment.

Simulated climate warming increases plant community heterogeneity in two types of boreal peatlands in north–central Canada

AbstractQuestionsClimate warming has been demonstrated to shift peatland plant community composition from Sphagnum mosses to vascular plants in Sphagnum‐dominated peatlands. However, fewer studies have determined how increasing temperature affects vegetation patterns in Carex‐dominated peatlands. As plants are important determinants of carbon storage potential in peatlands, we aim to determine how climate warming alters plant community composition in peatlands of two different vegetation types.LocationBoreal peatlands in north–central Ontario, Canada.MethodsIn a Sphagnum‐ and a Carex‐dominated peatland over two growing seasons, we instigated passive warming using clear open‐topped chambers, providing a modest increase (1–2°C) in temperature. In replicated plots we examined shifts in plant community composition using the point intercept method, and total above‐ground biomass using Leaf Area Index (LAI) against non‐warmed control plots.ResultsWhile there was no difference in species diversity between control and warmed plots in either fen site, warming significantly increased above‐ground biomass in the Carex‐dominated fen and decreased moss abundance in the Sphagnum‐dominated fen. Both fens also displayed significantly different plant community composition between warming and control plots, and increased heterogeneity under warming.ConclusionPeatlands are important global carbon stores and the plant community contributes to their carbon storage; Sphagnum mosses, in particular, are linked to high peatland carbon storage potential. Previous studies in Sphagnum‐dominated peatlands have shown concomitant declines in Sphagnum biomass and increases in vascular plant biomass, and in the short term, we show only a decline in Sphagnum. At both sites the increase in plant community heterogeneity suggests that climate warming effects on plant community composition in boreal peatlands may be more unpredictable than the literature suggests. Furthermore, this study demonstrates that plant community shifts occur even under modest warming scenarios.

Effects of Grazing, Wind Erosion, and Dust Deposition on Plant Community Composition and Structure in a Temperate Steppe

Grazing can affect plant community composition and structure directly by foraging and indirectly by increasing wind erosion and dust storms and subsequently influence ecosystem functioning and ecological services. However, the combined effects of grazing, wind erosion, and dust deposition have not been explored. As part of a 7-year (2010–2016) field manipulative experiment, this study was conducted to examine the impacts of grazing and simulated aeolian processes (wind erosion and dust deposition) on plant community cover and species richness in a temperate steppe on the Mongolian Plateau, China. Grazing decreased total cover by 4.2%, particularly the cover of tall-stature plants (> 20 cm in height), but resulted in 9.1% greater species richness. Wind erosion also reduced total cover by 17.0% primarily via suppressing short-stature plants associated with soil nitrogen loss, but had no effect on species richness. Dust deposition enhanced total cover by 5.7%, but resulted in a 7.3% decrease in species richness by driving some of the short-stature plant species to extinction. Both wind erosion and dust deposition showed additive effects with grazing on vegetation cover and species richness, though no detectable interaction between aeolian processes and grazing could be detected due to our methodological constraints. The changes in gross ecosystem productivity, ecosystem respiration, and net ecosystem productivity under the wind erosion and dust deposition treatments were positively related to aeolian process-induced changes in vegetation cover and species richness, highlighting the important roles of plant community shifts in regulating ecosystem carbon cycling. Our findings suggest that plant traits (for example, canopy height) and soil nutrients may be the key for understanding plant community responses to grassland management and natural hazards.

Density and habitat selection of mice on cheatgrass-invaded sites in British Columbia, Canada

Globally, invasive species in grasslands and shrublands have substantially altered trophic interactions and ecosystem processes. In North America, cheatgrass (Bromus tectorum) has invaded much of the western sage-steppe, leading to substantial shifts in plant communities and fire regimes. The effects of this cheatgrass invasion on small mammals are inconsistent among species and regions, and the mechanisms behind these patterns may be trophic or non-trophic. Cheatgrass alters cover and the amount of bare ground, thus affecting movements and predation risk, but cheatgreass also provides food for some rodents. We examined the extent to which low-density cheatgrass invasion (<20% cover) affected population densities and habitat selection of mice in southern British Columbia, Canada. In this region, Great Basin pocket mice (Perognathus parvus) were far more common than western harvest mice (Reithrodontomys megalotis) and deermice (Peromyscus maniculatus). Density of Great Basin pocket mice increased with bare ground and annual grasses, but decreased with shrub cover; when pocket mice foraged, they selected habitats with cheatgrass and bare, open ground. Cheatgrass did not predict movements of deermice or harvest mice. These results indicate that low cheatgrass densities may not be negative for these three species of mice, at least in the northern distribution of sage-steppe.

Biotic and Environmental Drivers of Plant Microbiomes Across a Permafrost Thaw Gradient.

Plant-associated microbiomes are structured by environmental conditions and plant associates, both of which are being altered by climate change. The future structure of plant microbiomes will depend on the, largely unknown, relative importance of each. This uncertainty is particularly relevant for arctic peatlands, which are undergoing large shifts in plant communities and soil microbiomes as permafrost thaws, and are potentially appreciable sources of climate change feedbacks due to their soil carbon (C) storage. We characterized phyllosphere and rhizosphere microbiomes of six plant species, and bulk peat, across a permafrost thaw progression (from intact permafrost, to partially- and fully-thawed stages) via 16S rRNA gene amplicon sequencing. We tested the hypothesis that the relative influence of biotic versus environmental filtering (the role of plant species versus thaw-defined habitat) in structuring microbial communities would differ among phyllosphere, rhizosphere, and bulk peat. Using both abundance- and phylogenetic-based approaches, we found that phyllosphere microbial composition was more strongly explained by plant associate, with little influence of habitat, whereas in the rhizosphere, plant and habitat had similar influence. Network-based community analyses showed that keystone taxa exhibited similar patterns with stronger responses to drivers. However, plant associates appeared to have a larger influence on organisms belonging to families associated with methane-cycling than the bulk community. Putative methanogens were more strongly influenced by plant than habitat in the rhizosphere, and in the phyllosphere putative methanotrophs were more strongly influenced by plant than was the community at large. We conclude that biotic effects can be stronger than environmental filtering, but their relative importance varies among microbial groups. For most microbes in this system, biotic filtering was stronger aboveground than belowground. However, for putative methane-cyclers, plant associations have a stronger influence on community composition than environment despite major hydrological changes with thaw. This suggests that plant successional dynamics may be as important as hydrological changes in determining microbial relevance to C-cycling climate feedbacks. By partitioning the degree that plant versus environmental filtering drives microbiome composition and function we can improve our ability to predict the consequences of warming for C-cycling in other arctic areas undergoing similar permafrost thaw transitions.

Vegetation changes in temperate ombrotrophic peatlands over a 35 year period.

Global changes in climate and land use are occurring at an unprecedented rate, often triggering drastic shifts in plant communities. This study aims to reconstruct the changes that occurred over 35 years in the plant communities of temperate bogs subjected to indirect human-induced disturbances. In 2015-17, we resurveyed the vascular flora of 76 plots located in 16 bogs of southern Québec (Canada) first sampled in 1982. We evaluated changes in species richness, frequency of occurrence and abundance, while considering species shade-tolerance and preferential habitat. We calculated beta diversity as between-site similarities in composition, and evaluated differences between the two surveys using tests for homogeneity in multivariate dispersion. We found a significant increase in species richness and beta diversity over the last 35 years associated with major species turnovers, indicating a biotic differentiation of the Sphagnum-bog plant communities. These changes were mostly associated with an increase in the abundance and frequency of shade-tolerant and facultative species, suggesting a global phenomenon of woody encroachment. Because the observed changes occurred in a few decades on sites free of in situ human disturbances, we suggest that they were likely induced by the synergic effect of the agricultural drainage occurring in the surrounding mineral soils, climate warming, and nitrogen atmospheric depositions. We also believe that further changes are to be expected, as the triggering factors persist. Finally, our results highlight the need for increased bog conservation or restauration efforts. Indeed, a rise in beta diversity due to the introduction of nearby terrestrial species could induce biotic homogenization of the bog flora with that of surrounding habitats and ultimately impoverish the regional species pool.

Plant community and phylogenetic shifts in acid seep springs over 49 years following Microstegium vimineum invasion

Community composition and diversity can change following exotic invasion. We tested the extent to which acid seep spring communities in southern Illinois had changed in composition and community heterogeneity based on three species surveys over 49 years. We also investigated the extent of changes in taxonomic and phylogenetic diversity since the invasion of Microstegium vimineum, an exotic grass. Floristic surveys of ten acid seep springs in southern Illinois were conducted in summer 2017 and compared to two previous surveys from 1968 and 2008. We investigated changes among acid seep springs and between surveys in species composition and community heterogeneity with multivariate ordination based on site dissimilarity, and univariate analyses comparing changes in taxonomic diversity (species richness and exotic species richness) and phylogenetic diversity [net relatedness (NRI) and nearest taxon indices (NTI)] determined from a species phylogeny based upon two plastid sequences (rbcL and matK). Acid seep spring communities became more compositionally similar to each other following woody plant encroachment and M. vimineum invasion. Total species richness declines were observed between surveys while exotic species richness increased. While NRI did not exhibit any temporal patterns, NTI significantly increased over time indicating that a decrease in phylogenetic diversity accompanied exotic invasion over almost half a century within these plant communities.

Pollen-based reconstruction of Holocene land-cover in mountain regions: Evaluation of the Landscape Reconstruction Algorithm in the Vicdessos valley, northern Pyrenees, France

Long-term perspectives on climate- and human-induced shifts in plant communities and tree line in mountains are often inferred from fossil pollen records. However, various factors, such as complex patterns of orographic wind fields and abundant insect-pollinated plants in higher altitudes, make pollen-based reconstruction in mountain regions difficult.Over the last decade the Landscape Reconstruction Algorithm (LRA) - a model-based approach in reconstruction of vegetation – has been successfully applied in various parts of the globe. However, evaluation of its effectiveness in mountain ranges is still limited. The present study assesses the extent to which the LRA approach helps quantify the local changes in vegetation cover at Vicdessos valley in northern French Pyrenees as a case study. In the study area well-dated sediment cores are available from eight bogs and ponds, 6–113 m in radius, located above the current tree line. We first use a simple simulation experiment to evaluate the way how pollen records from “landscape islands” (mountain tops and plateaus) would represent local vegetation and to clarify important factors affecting the LRA-based reconstruction in a mountainous region. This study then uses pollen records from these sites and vegetation and land-cover data both within a 50-km radius around the Vicdessos valley and within a 2-km radius from each site for evaluation of the REVEALS- and LOVE-based reconstruction of the regional and local plant cover, respectively, in the LRA approach. The land-cover data are complied for coniferous trees, broadleaved trees and non-forested areas from the CORINE and historical maps in three time windows: 1960–1970, 1990–2000 and 2000–2013.Major findings are as follows. (1) Accuracy of the regional vegetation estimates affects the reliability of the LRA-based reconstruction of vegetation within a 2-km radius; use of the CORINE data as input to the LOVE model improves reliability of the results over the use of the REVEALS-based estimates of regional vegetation. This implies that a systematic selection of pollen data only from sites above the tree line is problematic for estimating regional vegetation, and thus the entire LRA process. (2) Selection of the dispersal models for pollen transport (i.e. the Langrangian Stochastic Model vs. Gaussian Plume Model) does not affect significantly the LRA-based estimates at both the regional and local scales in the study area. (3) The LRA approach improves the pollen-based reconstruction of local vegetation compared to pollen percentage alone in northern Pyrenees. Although further empirical and simulation studies are necessary, our results emphasize the importance of site selection for the LRA-based reconstruction of vegetation in mountain regions.