Terrestrial Plant Communities Research Articles

A marine heatwave changes the stabilizing effects of biodiversity in kelp forests.

Biodiversity can stabilize ecological communities through biological insurance, but climate and other environmental changes may disrupt this process via simultaneous ecosystem destabilization and biodiversity loss. While changes to diversity-stability relationships (DSRs) and the underlying mechanisms have been extensively explored in terrestrial plant communities, this topic remains largely unexplored in benthic marine ecosystems that comprise diverse assemblages of producers and consumers. By analyzing two decades of kelp forest biodiversity survey data, we discovered changes in diversity, stability, and their relationships at multiple scales (biological organizational levels, spatial scales, and functional groups) that were linked with the most severe marine heatwave ever documented in the North Pacific Ocean. Moreover, changes in the strength of DSRs during/after the heatwave were more apparent among functional groups than both biological organizational levels (population vs. ecosystem levels) and spatial scales (local vs. broad scales). Specifically, the strength of DSRs decreased for fishes, increased for mobile invertebrates and understory algae, and were unchanged for sessile invertebrates during/after the heatwave. Our findings suggest that biodiversity plays a key role in stabilizing marine ecosystems, but the resilience of DSRs to adverse climate impacts primarily depends on the functional identities of ecological communities.

Extreme environments simplify reassembly of communities of arbuscular mycorrhizal fungi.

The ecological impacts of long-term (press) disturbance on mechanisms regulating the relative abundance (i.e., commonness or rarity) and temporal dynamics of species within a community remain largely unknown. This is particularly true for the functionally important arbuscular mycorrhizal (AM) fungi; obligate plant-root endosymbionts that colonize more than two-thirds of terrestrial plant species. Here, we use high-resolution amplicon sequencing to examine how AM fungal communities in a specific extreme ecosystem-mofettes or natural CO2 springs caused by geological CO2 exhalations-are affected by long-term stress. We found that in mofettes, specific and temporally stable communities form as a subset of the local metacommunity. These communities are less diverse and dominated by adapted, "stress tolerant" taxa. Those taxa are rare in control locations and more benign environments worldwide, but show a stable temporal pattern in the extreme sites, consistently dominating the communities in grassland mofettes. This pattern of lower diversity and high dominance of specific taxa has been confirmed as relatively stable over several sampling years and is independently observed across multiple geographic locations (mofettes in different countries). This study implies that the response of soil microbial community composition to long-term stress is relatively predictable, which can also reflect the community response to other anthropogenic stressors (e.g., heavy metal pollution or land use change). Moreover, as AM fungi are functionally differentiated, with different taxa providing different benefits to host plants, changes in community structure in response to long-term environmental change have the potential to impact terrestrial plant communities and their productivity.IMPORTANCEArbuscular mycorrhizal (AM) fungi form symbiotic relationships with more than two-thirds of plant species. In return for using plant carbon as their sole energy source, AM fungi improve plant mineral supply, water balance, and protection against pathogens. This work demonstrates the importance of long-term experiments to understand the effects of long-term environmental change and long-term disturbance on terrestrial ecosystems. We demonstrated a consistent response of the AM fungal community to a long-term stress, with lower diversity and a less variable AM fungal community over time under stress conditions compared to the surrounding controls. We have also identified, for the first time, a suite of AM fungal taxa that are consistently observed across broad geographic scales in stressed and anthropogenically heavily influenced ecosystems. This is critical because global environmental change in terrestrial ecosystems requires an integrative approach that considers both above- and below-ground changes and examines patterns over a longer geographic and temporal scale, rather than just single sampling events.

Different wildfire types promoted two-step terrestrial plant community change across the Triassic-Jurassic transition

Frequent wildfires associated with emplacement of the Central Atlantic Magmatic Province (CAMP) are thought to have been important drivers of two significant changes in terrestrial plant communities and diversity during the Triassic-Jurassic Mass Extinction (TJME, ca. 201.51 Ma). ​However, it remains to be investigated whether these two changes are potentially related to different wildfire types. To better understand this relationship, we used a new method to reanalyze fossil pollen and spores across the Triassic-Jurassic transition in the Jiyuan Basin from the North China Plate. Results show that two peaks in wildfire frequency experienced different types of wildfires, with each linked to significant changes in plant communities and diversity losses. In the first wildfire peak, canopy fires dominated and are accompanied by significant losses of canopy forming plants, while in the second wildfire peak, ground cover fires dominated accompanied by significant losses of ground cover plants. ​Changes in atmospheric humidity conditions were an important control on the two different wildfire peaks. Relatively humid climatic conditions corresponded to the prevalence of canopy fires and hindered the spread and development of ground cover fires in wet surface conditions. Conversely, relatively arid climatic conditions corresponded with the prevalence of ground cover fires in dry surface environments. Our results provide a potential relationship between terrestrial plant communities and wildfire types, which is important to further understanding of terrestrial environmental and floral changes driven by Large Igneous Provinces.

Legacy of salmon-derived nutrients on riparian soil chemistry and soil fertility on the Central Coast of British Columbia, Canada

Every year, salmon return to their natal streams to spawn. Their return represents an ecosystem subsidy of nutrients and energy from the sea to the land; these materials feed into terrestrial food webs, plant communities, and forest soils. Here we test the long term effects of salmon inputs on soil fertility by sampling soils from Haíɫzaqv (Heiltsuk) Nation territory on the Central Coast of British Columbia, Canada. A total of 20 soil chemical properties were assessed via two sampling methodologies: first, across 23 watersheds representing a regional gradient of salmon density (kg of salmon per meter of stream reach per year); and second, at four sites above and below waterfalls that blocked salmon migration. At each sampling point, soil material at two depths was collected. Multivariate analysis regional gradient showed salmon density, the moss community, and the shrub community to be significant factors related to soil chemistry. Similarly, being above or below the waterfall, the moss community, and the tree community were significant in the waterfall comparison. Generalized linear mixed models along regional salmon density gradient showed an increase in nitrate (NO3−) correlated with salmon inputs (p < 0.05), and moderately significant (p < 0.1) increases in ammonium (NH4+), phosphorus (P), aluminum (Al), and copper (Cu). Net cation exchange capacity (CEC) did not change; however, magnesium (Mg) significantly decreased along these gradients (p < 0.05), while sodium (Na) had a declining tendency and calcium (Ca) had an increasing tendency. Being below salmon-blocking waterfalls or the salmon density below falls was a factor in higher total nitrogen, nitrate, ammonium, phosphorus, total sulfur (S), magnesium, and sodium concentrations; below falls sites also had lower pH and aluminum. Exploratory analysis of the regional gradient data using a random forest model apportioned high importance to soil depth, the moss community, the shrub community, salmon density and distance from the stream. These results show that salmon inputs are correlated with a number of changes in recipient soils, and these are consistent with an interpretation of improved fertility at these sites.

Межэкотопические различия в видовом составе растительных сообществ с низким и высоким участием доминирующих видов

An increase in the dominant species participation in plant cover (increase in their projective cover, biomass, share in the total grass stand biomass) leads to change in the occurrence of many associated species, which may effect on the degree of difference (similarity) in the species composition of communities located in various habitats, and, accordingly, on the results of their classification. We considered this issue using the example of non-forest communities with high and low participation of certain dominants. The study area included the vicinity of the city of Maikop, the foothills and mountain ranges of the Western Caucasus (the basins of the Belaya and Bolshaya Laba rivers, 200–2500 m a. s. l.), as well as coastal areas of the Black Sea shelf and shallow areas of the Taman Bay of the Azov Sea (depths from 0.1 to 5 m). The objects of study were communities with varying degrees of participation of certain species, located in natural (semi-natural) and anthropogenic habitats of different types: 7 communities with the dominance of brown algae Ericaria bosphorica and Gongolaria barbata (Cystoseira sensu lato) (macrophytobenthos of the Black Sea), 6 — aquatic plants Zostera noltei and Z. marina (macrophytobenthos of the Azov Sea) and Solidago сanadensis (synanthropic communities), 5 each dominated by Calamagrostis arundinacea (subalpine meadows), Calamagrostis epigejos, Botriochloa ischaemum (low mountain meadows, synanthropic communities), Rubus caesius (edges and old fields) and Medicago falcata (synanthropic communities). Within each community 25–30 plots (0.5×0.5 m) were established. A sample of aboveground biomass was taken in each plot. For each of them were determined: 1) the weight of the wet biomass in general (W), the biomass of dominating (Wd) and associated species (Ws); 2) the degree of dominance (D = Wd / W), 3) the number and composition of associated species. For marine bottom communities, the Wd reflected the joint biomass of Ericaria bosphorica and Gongolaria barbata as well as Zostera noltei and Z. marina, respectively. In addition, since macrophytobenthos dominants may effect both negativly (competition) and positivly (protection, substrate) on other species, their participation in communities was assessed through absolute (Wd) biomass. From each series 10 samples with both the lowest (LD) and the highest (HD) dominant participation were selected. Data on species constancy in groups of LD biomass samples taken from 5 to 7 communities dominated by certain species were combined into one Table (infracenotic system, ICS), as well as data on species constancy in groups of samples with HD. The degree of differentiation of ICS with LD and with HD was assessed in two ways: 1) through the number of species considered as diagnostic for certain communities (the higher the number of such species, the higher the degree of differentiation of the ICS); 2) by visual comparison of the results of PCA-ordination of biomass samples with LD and with HD. The results show that an increase in the participation of dominants in non-forest terrestrial and marine bottom plant communities leads to a decrease in the constancy of associated species. As a result, some species lose their diagnostic status, while others become diagnostic ones. The number of the first in most cases is much higher than the second. Therefore, groups of samples with HD are characterized by a smaller number of diagnostic species than groups of samples with LD, and, accordingly, less differentiation. To a greater extent, this is expressed in communities with the dominance of Rubus caesius, Calamagrostis arundinacea, C. epigejos and Medicago falcata, and to a lesser extent, in communities with the dominance of Solidago сanadensis, as well as in macrophytobenthos. In addition only about 40 % of the species identified as diagnostic in groups of samples with HD are diagnostic for groups of samples with LD, taken from the same communities. Including, in communities with the dominance of Solidago canadensis — only 20 %, Zostera noltei and Z. marina — 25 %, Rubus caesius — 33 %. The PCA-ordination of groups of samples with low and high dominance of Calamagrostis arundinacea, Rubus caesius, Medicago falcata and Cystoseira s. l. shows slightly higher differentiation of the former (with LD) than the latter (with HD). In communities with low and high participation of other dominants, the differences in this regard are not pronounced. Thus, our results showed that groups of biomass samples with low and high participation of dominants, taken from the same communities, are characterized mainly by different numbers and composition of diagnostic species. This means that the results of the plant communities classification based on the ecological-floristic approach may depend, among other things, on the degree of species dominance in the sample plots. However, there is a circumstance that limits the significance of our results for the practice of syntaxonomic studies of terrestrial vegetation. It is associated with a significantly different size of sample plots that we used for biomass sampling (0.25 m2) and which are usually used for terrestrial communities (16–100 m2). In particular, if the influence of dominants on other species is indiscriminate, then it should be expected that its consequences for the community species richness, and, accordingly, the occurrence of species, will be clearly felt only in relatively small sites (Powell et al., 2011, 2013; Akatov et al., 2021, 2022; Afanasyev et al., 2022). The relevés of macrophytobenthos (sampling of biomass) are usually made on much smaller sample plots (0.1–0.25 m2). Therefore, for the practice of hydrobotanical research, our results may be more useful.

High intensity perturbations induce an abrupt shift in soil microbial state

Soil microbial communities play a pivotal role in regulating ecosystem functioning. But they are increasingly being shaped by human-induced environmental change, including intense “pulse” perturbations, such as droughts, which are predicted to increase in frequency and intensity with climate change. While it is known that soil microbial communities are sensitive to such perturbations and that effects can be long-lasting, it remains untested whether there is a threshold in the intensity and frequency of perturbations that can trigger abrupt and persistent transitions in the taxonomic and functional characteristics of soil microbial communities. Here we demonstrate experimentally that intense pulses of drought equivalent to a 30-year drought event (<15% WHC) induce a major shift in the soil microbial community characterised by significantly altered bacterial and fungal community structures of reduced complexity and functionality. Moreover, the characteristics of this transformed microbial community persisted after returning soil to its previous moisture status. As a result, we found that drought had a strong legacy effect on bacterial community function, inducing an enhanced growth rate following subsequent drought. Abrupt transitions are widely documented in aquatic and terrestrial plant communities in response to human-induced perturbations. Our findings demonstrate that such transitions also occur in soil microbial communities in response to high intensity pulse perturbations, with potentially deleterious consequences for soil health.

Deadly mushrooms of the genus Galerina found in Antarctica colonized the continent as early as the Pleistocene

Abstract Fungi are probably the most diverse group of eukaryotic organisms in the Antarctic continent and nearby archipelagos, and they dominate communities in either mild or harsh habitats. However, our knowledge of their global distribution ranges and the temporal origins of their Antarctic populations is rather limited or almost absent, especially for species that do not lichenize. We focused for the first time on elucidating the taxonomic identity and phylogenetic relationships of several Antarctic collections of the deadly fungal Basidiomycota genus Galerina. By using molecular sequence data from the universal fungal barcode and a dataset encompassing 178 specimens, the inferred phylogeny showed that the Antarctic specimens corresponded with the sub-cosmopolitan species Galerina marginata, Galerina badipes and Galerina fallax, and their most closely related intraspecific genetic lineages were from northern Europe and North America. We found that these species probably host Antarctic-endemic intraspecific lineages. Furthermore, our dating analyses indicated that their Antarctic populations originated in the Pleistocene, a temporal frame that agrees with that proposed for the Antarctic colonization of plants such as the grass Deschampsia antarctica, mosses and some amphitropical lichens. Altogether, these findings converge on the same temporal scenario for the assembly of the most conspicuous terrestrial Antarctic plant and fungal communities.

Two common, often coexisting grassland plant species differ in their evolutionary potential in response to experimental drought.

For terrestrial plant communities, the increase in frequency and intensity of drought events is considered as one of the most severe consequences of climate change. While single-species studies demonstrate that drought can lead to relatively rapid adaptive genetic changes, the evolutionary potential and constraints to selection need to be assessed in comparative approaches to draw more general conclusions. In a greenhouse experiment, we compare the phenotypic response and evolutionary potential of two co-occurring grassland plant species, Bromus erectus and Trifolium pratense, in two environments differing in water availability. We quantified variation in functional traits and reproductive fitness in response to drought and compared multivariate genetic variance-covariance matrices and predicted evolutionary responses between species. Species showed different drought adaptation strategies, reflected in both their species-specific phenotypic plasticity and predicted responses to selection indicating contrasting evolutionary potential under drought. In T. pratense we found evidence for stronger genetic constraints under drought compared to more favourable conditions, and for some traits plastic and predicted evolutionary responses to drought had opposing directions, likely limiting the potential for adaptive change. Our study contributes to a more detailed understanding of the evolutionary potential of species with different adaptive strategies in response to climate change and may help to inform future scenarios for semi-natural grassland ecosystems.

Mechanism of Terrestrial Plant Community Assembly under Different Intensities of Anthropogenic Disturbance in Dianchi Lakeside

A lakeside is a functional transition zone that connects the lake aquatic ecosystem and the land ecosystem. Understanding the community assembly mechanism is crucial for regional ecological restoration, habitat management, and biodiversity conservation. However, research on the terrestrial plant community assembly in lakesides under anthropogenic disturbance is still lacking. The present study used phylogeny and functional traits to assess the community assembly of three habitat types with different anthropogenic disturbances in Dianchi lakeside. The factors that influenced the community assembly were also explored. Results indicated that the phylogenetic signals of all the examined functional traits of the dominant species were weak, suggesting that the traits were convergent. The community phylogenetic and functional structures of the different habitat types showed random patterns. Thus, the assembly of terrestrial plant communities in the three habitat types was driven by competitive exclusion and neutral processes in Dianchi lakeside. The trait trade-off strategies of species in the different habitats varied with the different habitat types. Anthropogenic disturbance played an important role in the process of community assembly. The present study provides a scientific basis for the assessment and management of ecological restoration in Dianchi lakeside and other plateau lakes and enriches the knowledge on the community assembly mechanism of disturbed plant communities.

Late Barremian–Aptian paleoenvironmental variations and OAE1a environmental effect in the eastern Crimea

The early Aptian Oceanic Anoxic Event 1a (OAE1a, or Selli Event) is widely known from many oceanic and inland sections as an interval of enhanced accumulation of sediments rich in total organic carbon (TOC), associated with the turnover in the global carbon budget and dramatic biotic variations. Our multidisciplinary study of the upper Barremian to lower upper Aptian deposits from the eastern part of Crimean Peninsula allowed us to confirm the presence of a layer that correlates to OAE1a and revealed significant reorganization in the planktonic and benthic foraminifera, nannofossils, ostracod and terrestrial plant communities at this level. The low-calcareous OAE1a deposits from the eastern Crimea lack in TOC that is not typical sedimentological response to this critical event. The OAE1a onset was associated with a nannoconid crisis, occurrence of low-abundance Hedbergella planktonic foraminifera, increased abundance of benthic foraminifera and ostracods and the bloom of Classopolis on the adjacent land. The calcareous microplankton biota was highly oppressed during OAE1a up to total elimination in the core of the event. Benthic assemblages indicate the occurrence of dysoxic conditions at the sea-floor. The absence of organic matter in the deposits of the OAE1a interval points to the low basinal biotic productivity and low input of terrestrial organic matter. We suggest that oligotrophication of the basin was related to the transgressive pulse, which led to small-scale landward moving of the coastal line barriered by coastal highland. The hot arid climatic conditions indicated by terrestrial plants, prevented the supply of nutrients and terrestrial organic matter into the basin that caused low algal and bacterial productivity and prevented accumulation of TOC-rich sediments. The termination of OAE1a coincides with the occurrence of warm humid climate and erosion of ephemeral coastal highland, more likely, built up by soft clayey sediments. The transit restoration of the normal marine biota in the early late Aptian was interrupted in the middle late Aptian by new long-lived regression led to enhanced terrestrial runoff and, possibly, fresh water input killed marine biota and caused the accumulation of low-calcareous clay.

Climate-trait relationships exhibit strong habitat specificity in plant communities across Europe

Ecological theory predicts close relationships between macroclimate and functional traits. Yet, global climatic gradients correlate only weakly with the trait composition of local plant communities, suggesting that important factors have been ignored. Here, we investigate the consistency of climate-trait relationships for plant communities in European habitats. Assuming that local factors are better accounted for in more narrowly defined habitats, we assigned > 300,000 vegetation plots to hierarchically classified habitats and modelled the effects of climate on the community-weighted means of four key functional traits using generalized additive models. We found that the predictive power of climate increased from broadly to narrowly defined habitats for specific leaf area and root length, but not for plant height and seed mass. Although macroclimate generally predicted the distribution of all traits, its effects varied, with habitat-specificity increasing toward more narrowly defined habitats. We conclude that macroclimate is an important determinant of terrestrial plant communities, but future predictions of climatic effects must consider how habitats are defined.

The salmonid and the subsurface: Hillslope storage capacity determines the quality and distribution of fish habitat

AbstractWater in rivers is delivered via the critical zone (CZ)—the living skin of the Earth, extending from the top of the vegetation canopy through the soil and down to fresh bedrock and the bottom of significantly active groundwater. Consequently, the success of stream‐rearing salmonids depends on the structure and resulting water storage and release processes of this zone. Physical processes below the land surface (the subsurface component of the CZ) ultimately determine how landscapes “filter” climate to manifest ecologically significant streamflow and temperature regimes. Subsurface water storage capacity of the CZ has emerged as a key hydrologic variable that integrates many of these subsurface processes, helping to explain flow regimes and terrestrial plant community composition. Here, we investigate how subsurface storage controls flow, temperature, and energetic regimes that matter for salmonids. We illustrate the explanatory power of broadly applicable, storage‐based frameworks across a lithological gradient that spans the Eel River watershed of California. Study sites are climatically similar but differ in their geologies and consequent subsurface CZ structure that dictates water storage dynamics, leading to dramatically different hydrographs, temperature, and riparian regimes—with consequences for every aspect of salmonid life history. Lithological controls on the development of key subsurface CZ properties like storage capacity suggest a heretofore unexplored link between salmonids and geology, adding to a rich literature that highlights various fluvial and geomorphic influences on salmonid diversity and distribution. Rapidly advancing methods for estimating and observing subsurface water storage dynamics at large scales present new opportunities for more clearly identifying landscape features that constrain the distributions and abundances of organisms, including salmonids, at watershed scales.

Experimental addition of marine-derived nutrients affects wildflower traits in a coastal meta-ecosystem.

Organismal movement can bring individuals, resources and novel interactions across ecosystem boundaries and into recipient habitats, thereby forming meta-ecosystems. For example, Pacific salmon ecosystems receive large marine-derived nitrogen subsidies during annual spawning events, which can have a wide range of effects on aquatic and terrestrial plant species and communities. In this study, we evaluate the effects of cross-ecosystem nutrient subsidies on terrestrial plant growth and reproduction. We conducted a large-scale field experiment with four treatments: (i) addition of a pink salmon (Oncorhynchus gorbuscha) carcass, (ii) addition of the drift seaweed rockweed (Fucus distichus), (iii) addition of both salmon + rockweed, and (iv) a control. We examined treatment effects on leaf nitrogen and fitness-associated floral traits in four common estuarine wildflower species. We found elevated leaf ∂15N in all plant species and all sampling years in treatments with salmon carcass additions but did not observe any differences in leaf per cent nitrogen. We also observed larger leaf area in two species, a context-dependent increase in floral display area in two species, and a limited increase in plant seed set in response to both salmon carcass treatments. In sum, our study suggests that marine nutrients can affect terrestrial plant growth and reproduction.

Culturable microorganisms of substrates of terrestrial plant communities of the maritime Antarctic (Galindez Island, Booth Island)

Culturable microorganisms of substrates of terrestrial plant communities of the maritime Antarctic (Galindez Island, Booth Island)

Marine subsidies produce cactus forests on desert islands

In island systems, nitrogen-rich seabird guano is a marine subsidy that can shape terrestrial plant communities. In zones of nutrient upwelling such as the Gulf of California, copious seabird guano is commonplace on bird islands. Several bird islands host regionally unique cactus forests, especially of the large columnar cactus, cardón (Pachycereus pringlei). We show that a chain of interactions across the land-sea interface yields an allochthonous input of nitrogen in the form of seabird guano, fueling the production of some of the densest cactus populations in the world. Fish, seabird, guano, soil, and cactus samples were taken from the representative seabird island of San Pedro Mártir for nitrogen stable isotope ratio measurements, which were compared to soil and cactus samples from other seabird and non-seabird Gulf islands and terrestrial ecosystems throughout the range of the cardón. Isla San Pedro Mártir δ15N values are distinctively high, ranging from fish + 17.7, seabird + 19.7, guano + 14.8, soil + 34.3 and cactus + 30.3 compared to average values across non-bird sites of + 13.0 (N = 213, S.D. = 3.7) for soil and + 9.8 (N = 212, S.D. = 3.4) for cactus. These δ15N values are among the highest ever reported for plants. Seabird island soil and cactus δ15N values were consistently significantly enriched relative to mainland and non-bird islands, a relationship expected due to the progressive volatilization of 14N rich ammonia from decomposing guano deposits. Our findings demonstrate that seabird-mediated marine nutrient deposits provide the source for solubilized nitrogen on desert islands, which stimulate terrestrial plant production in the cardón cactus beyond that seen in either mainland ecosystems or non-seabird islands.

Competition for soil resources forces a trade-off between enhancing tree productivity and understorey species richness in managed beech forests

Traditionally focussed on maximising productivity, forest management increasingly has to consider other functions performed by the forest stands, such as biodiversity conservation. Terrestrial plant communities typically possess a hump-back relationship between biomass productivity and plant species richness. However, there is evidence of a reverse relationship in forests dominated by beech, one of the most competitive and widespread tree species in temperate Europe. To fully explore the tree productivity-species richness relationship, we investigated above- and below-ground drivers of understorey plant species richness. We focussed on managed beech forests growing along an elevation gradient in Central Europe. We found that the lowest understorey plant diversity was under conditions optimal for beech. Tree fine root mass, canopy openness, soil C/N ratio, the interaction between tree fine root mass and stoniness, and stand structural diversity explain the variation of understorey species richness. We show that the competition for soil resources is the main driver of plant species diversity in managed forests; maximising beech growth in optimal conditions may thus come at the expense of understorey plant richness.

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.

Synchronous vegetation response to the last glacial-interglacial transition in northwest Europe

The North Atlantic region experienced abrupt high-amplitude cooling at the onset of the Younger Dryas stadial. However, due to chronological uncertainties in the available terrestrial records it is unclear whether terrestrial ecosystem response to this event was instantaneous and spatially synchronous, or whether regional or time-transgressive lags existed. Here we use new palynological results from a robustly dated lake sediment sequence retrieved from lake Hämelsee (north Germany) to show that vegetation change started at 12,820 cal. yr BP, concurrent with the onset of changes in local climate. A comparison of the Hämelsee results to a compilation of precisely dated palynological records shows instant and, within decadal-scale dating uncertainty, synchronous response of the terrestrial plant community to Late-Glacial climate change across northwest Europe. The results indicate that the environmental impact of climate cooling was more severe than previously thought and illustrates the sensitivity of natural terrestrial ecosystems to external forcing.

Local differences in paleohydrology have stronger influence on plant biomarkers than regional climate change across two Paleogene Laramide Basins, Wyoming, USA

Plant biomarkers in the geologic record are commonly used to reconstruct paleovegetation and paleoclimate. Yet the representativeness of these biomarker-based reconstructions is not entirely straightforward because both local and regional climatic influences are convolved in the recovered biomarker composition. Furthermore, geomorphic processes including sedimentation, deposition, burial rates, and surface and groundwater levels can also influence biomarker preservation and taphonomy. The combination of leaf compression fossils with the biomarker record provides a robust framework in which ecological reconstructions can be made. Herein we present a case study examining the biomarker responses to a major regional climatic signal, the Paleocene Eocene Thermal Maximum (PETM), from local effects in two basins with different paleohydrology: the Hanna Basin (HB) and Bighorn Basin (BHB), in Wyoming (USA). Data collected include (1) leaf wax n-alkanes and plant-derived non-steroidal di- and triterpenoids, (2) pristane/phytane vs. terrestrial to aquatic ratio (Pr/Ph:TAR), plant material source proxy (Paq), hopanes, and bacteria which provide constraints on organic matter sourcing, redox conditions, and bacterial inputs, and (3) carbon (δ13Cn-alk) and hydrogen (δ2Hn-alk) isotopic compositions of plant wax n-alkanes. We find the two basins differed significantly in weight % total organic carbon (TOC), alkane and terpenoid concentrations, and δ13Cn-alk and δ2Hn-alk values. We examined the effects of δ13Catm on δ13Cn-alk values by assuming comparable regional climate in the two basins. Differences in paleohydrology and paleovegetation were assessed using the above proxies and previously published paleobotanical data. Local paleohydrologic conditions, an abiotic factor, likely drove variability in plant biomarker preservation and paleovegetation structure. Notably, an abundance of water in the HB during the PETM created a conifer refugium while drying within the BHB caused a local extirpation. This study highlights the importance of considering the influence of local environment, specifically paleohydrology, on the local fossil record and the need to compare multiple sites to disentangle regional climate effects on terrestrial plant communities. Distinguishing local from regional differences is imperative if we are to understand how ecosystems respond to future climate change.

Vegetation changes over the last centuries in the Lower Lake Constance region reconstructed from sediment‐core environmental DNA

AbstractMany European lake ecosystems, including their respective catchment areas, underwent anthropogenic environmental changes over the last centuries. This has resulted in changes in the aquatic and terrestrial vegetation, but historical records on the composition of the past vegetation on centennial scale are scarce. In this study, we examined changes in the terrestrial and aquatic plant communities in and around Lower Lake Constance using metabarcoding of sedimentary DNA (sedDNA) of three cores from different sub‐basins covering the past, up to 300 years. We successfully identified an average of c. 3000 sequence variants (molecular operational taxonomic units ‐ MOTUs) and obtained a taxonomically annotated dataset of 127 species, 104 genera, and 72 families. We could detect major changes in the terrestrial and aquatic vegetation of the Lower Lake Constance region by examining the cores. For example, alpha diversity decreased in the last c. 100 years, and this decrease was more pronounced in the terrestrial than in the aquatic plant community. Unlike the terrestrial plant community, the current aquatic plant‐community composition partially resembles the community from before the 20th‐century eutrophication phase of the lake. In addition to changes that can be attributed to anthropogenic impacts, we also captured the effect of DNA sedimentation on the terrestrial DNA diversity representation in sediments during periods of extensive flooding and potentially as a consequence of extremely cold winters. With sedDNA from Lower Lake Constance, we provide a new local dataset to investigate and extend the historical changes of different shoreline habitats and to identify characteristic and invasive plant species. Such highly resolved datasets spanning the past centuries can provide detailed information on human environmental history in densely populated regions that have undergone severe changes in the recent past.