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The wolf (Canis lupus) is arguably the most successful species at recolonizing its now human‐dominated former ranges in Europe and North America. Over the centuries while the wolf was absent, humans have transformed ecosystems to a large extent. In this paper, we highlight key aspects of these human‐modified ecosystems that include changes to (meso)carnivore communities, wolves themselves (genetics, behaviour), woody plant communities and the playing field for predator–prey interactions (landscape structure).We argue that the recognition of the novelty of human‐modified ecosystems logically leads to novel pathways of how wolves can influence ecosystem functioning. Thus far, the ecological impacts of wolves in human‐dominated systems have largely been predicted based on the documented effects they have on prey species or lower trophic levels in well‐preserved systems with low human impact. However, wolves in human‐modified ecosystems will engage in an array of novel interactions and potential novel trophic cascades that do not occur in more natural ecosystems with lower human impact.This should encourage us to re‐assess the questions we ask about wolf impacts in novel systems. A promising direction for future studies is exploring what novel interactions establish and under what conditions wolves can exert their ecosystem impacts (context dependence) in the human‐modified ecosystems wolves are recolonizing.Policy implications. Understanding these novel interactions and the context dependence of ecosystem impacts could guide us to act to improve conditions to enable wolves to exert their ecosystem impacts again. These novel interactions may be the true ecological and societal value of having wolves returning to human‐modified landscapes. [ABSTRACT FROM AUTHOR]

Native species that are abundant and persistent across disturbance‐succession cycles can affect recovery and restoration of plant communities, especially in drylands. In the sagebrush‐steppe deserts of North America, restoring deep‐rooted perennial bunchgrasses (DRPBGs) is key to the strategy for breaking an increasingly problematic cycle of wildfire promoted by exotic annual grasses (EAGs) and displacement of perennials by post‐fire increases in EAGs. We asked how Sandberg bluegrass (Poa secunda, POSE)—a common native grass that shares traits with EAGs such as resilience to disturbance and rapid, shallow‐rooted, early season growth—(1) recovered after wildfire, (2) responded to different combinations of native‐plant seedings of DRPBGs and EAG‐targeting herbicides; and (3) in turn, related to DRPBG recovery. In repeated sampling of up to approximately 2,000 plots spanning 113,000 burned hectares, POSE was initially more abundant than DRPBGs until POSE began to decline 5 years post‐fire, and POSE was marginally affected or unaffected by restoration treatments targeting DRPBGs or EAGs. In comparison, EAG cover decreased 8–16% where preemergent herbicide was sprayed and DRPBG cover increased 3–9% where they were drill‐seeded, and the greatest EAG reductions and DRPBG increases were seen where seeding and herbicides were combined in a time‐staggered fashion. Treatments had less target effects where POSE cover was high (>18%), which is also where EAG cover was scarcer and DRPBG cover greater, regardless of post‐fire interventions. Consideration of the ecological role of disturbance‐resilient species with ruderal characteristics that match traits of key invaders may improve the efficiency and effectiveness of restoration interventions. [ABSTRACT FROM AUTHOR]

Questions: Rapid climate change in northern latitudes is expected to influence plant functional traits of the whole community (community‐level traits) through species compositional changes and/or trait plasticity, limiting our ability to anticipate climate warming impacts on northern plant communities. We explored differences in plant community composition and community‐level traits within and among four boreal peatland sites and determined whether intra‐ or interspecific variation drives community‐level traits. Location: Boreal biome of western North America. Methods: We collected plant community composition and functional trait data along dominant topoedaphic and/or hydrologic gradients at four peatland sites spanning the latitudinal extent of the boreal biome of western North America. We characterized variability in community composition and community‐level traits of understorey vascular and moss species both within (local‐scale) and among sites (regional‐scale). Results: Against expectations, community‐level traits of vascular plant and moss species were generally consistent among sites. Furthermore, interspecific variation was more important in explaining community‐level trait variation than intraspecific variation. Within‐site variation in both community‐level traits and community composition was greater than among‐site variation, suggesting that local environmental gradients (canopy density, organic layer thickness, etc.) may be more influential in determining plant community processes than regional‐scale gradients. Conclusions: Given the importance of interspecific variation to within‐site shifts in community‐level traits and greater variation of community composition within than among sites, we conclude that climate‐induced shifts in understorey community composition may not have a strong influence on community‐level traits in boreal peatlands unless local‐scale environmental gradients are substantially altered. [ABSTRACT FROM AUTHOR]

A history of species co‐occurrence in plant communities is hypothesized to lead to greater niche differentiation, more efficient resource partitioning, and more productive, resistant communities as a result of evolution in response to biotic interactions. A similar question can be asked of co‐occurring populations: do individual species or community responses differ when communities are founded with plants sharing a history of population co‐occurrence (sympatric) or originating from different locations (allopatric)? Using shrub, grass, and forb species from six locations in the western Great Basin, North America, we compared establishment, productivity, reproduction, phenology, and resistance to invaders for experimental communities with either sympatric or allopatric population associations. Each community type was planted with six taxa in outdoor mesocosms, measured over three growing seasons, and invaded with the annual grass Bromus tectorum in the final season. For most populations, the allopatric or sympatric status of neighbors was not important. However, in some cases, it was beneficial for some species from some locations to be planted with allopatric neighbors, while others benefited from sympatric neighbors, and some of these responses had large effects. For instance, the Elymus population that benefited the most from allopatry grew 50% larger with allopatric neighbors than in single origin mesocosms. This response affected invasion resistance, as B. tectorum biomass was strongly affected by productivity and phenology of Elymus spp., as well as Poa secunda. Our results demonstrate that, while community composition can affect plant performance in semi‐arid plant communities, assembling communities from sympatric populations is not sufficient to ensure high productivity and invasion resistance. Instead, we observed an idiosyncratic interaction between sampling effects and evolutionary history, with the potential for seed source of individual populations to have community‐level effects. [ABSTRACT FROM AUTHOR]

Root hemiparasitic plants both compete with and extract resources from host plants. By reducing the abundance of dominant plants and releasing subordinates from competitive exclusion, they can have an outsized impact on plant communities. Most research on the ecological role of hemiparasites is manipulative and focuses on a small number of hemiparasitic taxa. Here, we ask whether patterns in natural plant communities match the expectation that hemiparasites affect the structure of plant communities. Our data were collected on 129 national park units spanning the continental United States. The most common hemiparasite genera were Pedicularis, Castilleja, Krameria, and Comandra. We used null models and linear mixed models to determine whether hemiparasites were associated with changes in community richness and evenness. Hemiparasite presence did not affect community metrics. Hemiparasite abundance was positively associated with increasing evenness of herbaceous species, but not with species richness. The associations that we observed on a continental scale are consistent with evidence that the impacts of root hemiparasitic plants on evenness can be substantial and abundance dependent but that effects on richness are less pronounced. Hemiparasites mediate competitive exclusion in communities to facilitate species coexistence and merit consideration of inclusion in ecological theories of coexistence. [ABSTRACT FROM AUTHOR]

Characterizing correlates of phytochemical resistance trait variation across a landscape can provide insight into the ecological factors that have shaped the evolution of resistance arsenals. Using field‐collected data and a greenhouse common garden experiment, we assessed the relative influences of abiotic and biotic drivers of genetic‐based defense trait variation across 41 yellow monkeyflower populations from western and eastern North America and the United Kingdom. Populations experience different climates, herbivore communities, and neighboring vegetative communities, and have distinct phytochemical resistance arsenals. Similarities in climate as well as herbivore and vegetative communities decline with increasing physical distance separating populations, and phytochemical resistance arsenal composition shows a similarly decreasing trend. Of the abiotic and biotic factors examined, temperature and the neighboring vegetation community had the strongest relative effects on resistance arsenal differentiation, whereas herbivore community composition and precipitation have relatively small effects. Rather than simply controlling for geographic proximity, we jointly assessed the relative strengths of both geographic and ecological variables on phytochemical arsenal compositional dissimilarity. Overall, our results illustrate how abiotic conditions and biotic interactions shape plant defense traits in natural populations. [ABSTRACT FROM AUTHOR]

Aim: Nitrogen (N)‐fixing plants are an important component of global plant communities, but the drivers of N‐fixing plant diversity, especially in temperate regions, remain underexplored. Here, we examined broad‐scale patterns of N‐fixing and non‐fixing plant phylogenetic diversity (PD) and species richness (SR) across a wide portion of temperate North America, focusing on relationships with soil N and aridity. We also tested whether exotic species, with and without N‐fixing symbiosis, have fewer abiotic limitations compared with native species. Location: USA and Puerto Rico. Time period: Current. Major taxa studied: Vascular plants, focusing on N‐fixing groups (orders Fabales, Fagales, Rosales and Cucurbitales). Methods: We subset National Ecological Observatory Network (NEON) plant plot data from all sites along two axes (N fixing–non‐N fixing and native–exotic), calculating plot‐level SR, PD and mean pairwise phylogenetic distance (MPD). We then used linear mixed models to investigate relationships between diversity values and key soil measurements, along with aridity, temperature and fire frequency. Results: Aridity was the sole predictor of proportional phylogenetic diversity of N fixers. The SR of N fixers still decreased marginally in arid regions, whereas native N‐fixer MPD increased with aridity, indicative of unique lineages of N fixers in the driest conditions, in contrast to native non‐N fixers. The SR of both native N fixers and non‐N fixers increased in low‐N soils. Aridity did not affect SR of exotic non‐N fixers, unlike other groups, whereas exotic N fixers showed lower MPD in increasingly high‐N soils, suggesting filtering, contrary what was found for native N fixers. Main conclusions: Our results suggest that it is not nitrogen, or any soil nutrient, that has the strongest effect on the relative success of N fixers in plant communities. Rather, aridity is the key driver, at least for native species, in line with empirical results from other biomes and increased understanding of N fixation as a key mechanism to avoid water loss. [ABSTRACT FROM AUTHOR]

Motivation: Rapid climate change is altering plant communities around the globe fundamentally. Despite progress in understanding how plants respond to these climate shifts, accumulating evidence suggests that disturbance could not only modify expected plant responses but, in some cases, have larger impacts on compositional shifts than climate change. Climate‐driven disturbances are becoming increasingly common in many biomes and are key drivers of vegetation dynamics at both species and community levels. Palaeoecological records provide valuable observational windows for elucidating the long‐term impacts of these disturbances on plant dynamics; however, sparse resolution and difficulty in disentangling drivers of change limit our ability to understand the impact of disturbance on plant communities. In this targeted review, we highlight emerging opportunities in palaeoecology to advance our understanding about how disturbance, especially fire, impacts the ecological and evolutionary dynamics of terrestrial plant communities. Location: Global examples, with many from North America. Conclusions: We propose a set of palaeoecological and integrative approaches that could greatly enhance our understanding of how disturbance regimes influence global plant dynamics. Specifically, we identify four future study areas: (1) focus on palaeoecological disturbance proxies beyond fire and leverage multi proxy research to examine the influence of interacting disturbances on plant community dynamics; (2) use advances in disturbance and vegetation reconstructions, including ancient sedimentary DNA, to provide the spatial, temporal and taxonomic resolution needed to resolve the relationship between changing disturbance regimes and corresponding shifts in plant community composition; (3) integrate palaeoecological, archaeological and Indigenous knowledge to disentangle the complex interplay between climate, human land use, fire and vegetation structure; and (4) apply "functional palaeoecology" and the synergy between palaeoecology and genetics to understand how fire disturbance has served as a long‐standing selective agent on plants. These frameworks could increase the resolution of disturbance‐driven plant dynamics, potentially providing valuable information for future management. [ABSTRACT FROM AUTHOR]

In recent years, there has been an increasing recognition of the role humans play in the structure, composition, and function of ecosystems. Ethnoecological documentation of traditional management systems of Indigenous Peoples in northwestern North America has contributed significantly to this rethinking. A less well‐recognized but foundational part of traditional management of this region is the practice of transplanting plants and plant propagules to expand the range and accessibility of culturally valued plants. In part, the lack of recognition of such translocations has to do with difficulties in identifying evidence of such actions from the past. Here, we summarize various lines of evidence, including that from ethnographic and ethnohistoric records, languages, oral traditions, phytogeography, and archaeology, to document the widespread and long‐standing extent of plant translocation practices among Indigenous Peoples of northwestern North America. Furthermore, we demonstrate how such practices have helped shape contemporary native plant communities throughout the region. Recognizing these past contributions to current ecological contexts honors Indigenous heritage and Indigenous Peoples' long‐term relationships with their biological worlds. [translocation, transplanting, ethnobotany, traditional resource management, northwestern North America] [ABSTRACT FROM AUTHOR]

Questions: Biosolids are a source of nutrient‐rich organic material that can be used to improve degraded or disturbed soils. Research on vegetation responses to the land application of biosolids has increased in the past 20 years, but there is no consensus on how plant communities respond to biosolids applications. What factors influence productivity and vegetative cover following biosolids application for grassland reclamation? How does the addition of biosolids impact plant community responses? Location: Global, but predominantly North America and Europe. Methods: To explore vegetative responses following biosolids application, we used a global systematic review and meta‐analysis of 59 articles. Our meta‐analysis used the log response ratio (LRR) as an effect size for productivity, total cover, species richness, diversity and exotic species abundance and explored covariates addressing various site characteristics and reclamation strategies. Results: We found that across sites, the land application of biosolids significantly increased productivity and cover but had no significant overall effect on species richness, Shannon diversity or exotic species abundance on degraded lands. These increases in the LRR for productivity and vegetative cover were lower on sites that experienced a fire prior to biosolids application. Climatic variables like mean annual temperature were shown to alter the response of vegetative cover, where warmer sites tended to have more positive responses to biosolids. Seeding was found to increase plant cover but decrease species richness early in the reclamation process. Conclusions: This area of research is growing; most of the publications we used come from the last 20 years and were mostly conducted in North America and Europe. While we can build on the present literature, there is clearly room for more research to ensure the process of reclaiming degraded ecosystems using biosolids results in desired plant communities, e.g. high native species diversity. Future research should consistently report biosolids chemical characteristics as well as application and processing methodologies. [ABSTRACT FROM AUTHOR]

Fires shape the biogeochemistry and functioning of many ecosystems, and fire frequencies are changing across much of the globe. Frequent fires can change soil carbon (C) and nitrogen (N) storage by altering the quantity and chemistry of plant inputs through changes in plant biomass and composition as well as the decomposition of soil organic matter. How decomposition rates change with shifting inputs remains uncertain because most studies focus on the effects of single fires, where transient responses may not reflect responses to decadal changes in burning frequencies. Here, we sampled seven sites exposed to different fire frequencies. In four of the sites, we intensively sampled both soils and plant communities across four ecosystems in North America and Africa spanning tropical savanna, temperate coniferous savanna, temperate broadleaf savanna, and temperate coniferous forest ecosystems. Each site contained multiple plots burned frequently for 33–61 years and nearby plots that had remained unburned over the same period replicated at the landscape scale. Across all sites, repeatedly burned plots had 25–185% lower bulk soil C and N concentrations but also 2–10‐fold lower potential decomposition of organic matter compared to unburned sites. Soil C and N concentrations and extracellular enzyme activities declined with frequent fire because fire reduced both plant biomass inputs into soils and dampened the localized enrichment effect of tree canopies. Examination of soil extracellular enzyme activities revealed that fire decreased the potential turnover of organic matter in the forms of cellulose, starch, and chitin (P < 0.0001) but not polyphenol and lignin (P = 0.09), suggesting a shift in soil C and N cycling. Inclusion of δ13C data from three additional savanna sites (19–60 years of altered fire frequencies) showed that soil C losses were largest in sites where estimated tree inputs into soils declined the most (r2 = 0.91, P < 0.01). In conclusion, repeated burning reduced C and N storage, consistent with previous studies, but fire also reduced potential decomposition, likely contributing to slower C and N cycling. Trees were important in shaping soil C and N responses across sites, but the magnitude of tree effects differed and depended on how tree biomass inputs into soil responded to fire. [ABSTRACT FROM AUTHOR]

Aim: The functional trait composition of plant communities is thought to be determined largely by climate, but relationships between contemporary trait distributions and climate are often weak. Spatial mismatches between trait and climatic conditions are commonly thought to arise from disequilibrium responses to past environmental changes. We aimed to investigate whether current trait–climate disequilibrium is likely to emerge during plant functional responses to Holocene climate warming. Location: North America. Time period: 14–0 ka. Major taxa studied: Terrestrial plants. Methods: We joined global trait data with palaeoecological time series and climate simulations on 425 sites. We estimated plant community functional composition for three leaf traits involved in resource use. We then quantified disequilibrium in plant trait temporal responses to climate change during two contrasted periods: a period of high climate variability (14–7 ka) and a period of low climate variability (7–0 ka). Results: Functional trait composition showed consistent deviation from climatic equilibrium during both periods. The temporal dynamics of trait composition tends to be positively correlated with climate equilibrium expectations during Holocene climate warming (14–7 ka), but not during a subsequent period of low climate variability (7–0 ka). Main conclusions: Long‐term functional responses of plants to climate change showed mixed evidence for both equilibrium and disequilibrium responses. Temporal trait dynamics were closer to the expectations of spatial dynamics under high climate variability, indicating that the relevance of space‐for‐time substitution might be dependent, in part, on climate variability. Our results also suggest that current mismatches between trait and climatic conditions might arise because of a divergence of factors influencing trait dynamics during periods of low climate variability. These findings provide a counterpoint to the common assumption that contemporary trait–climate mismatches result from lagged responses to past climate warming. Our study also demonstrates the need for a deeper investigation of the potential influence of non‐climatic factors on functional plant community dynamics. [ABSTRACT FROM AUTHOR]

Background: Ecological disturbance is a major driver of ecosystem structure and evolutionary selection, and theory predicts that the frequency and/or intensity of disturbance should determine its effects on communities. However, adaptations of species pools to different historical disturbance regimes are rarely considered in the search for generalizable community responses to disturbance. To explore how the severity of disturbance affects plant diversity patterns, we review studies of understorey plant community responses to wildfire in conifer forests of western North America across a gradient of departure from historical fire regimes. Review findings: We find that post‐fire plant species richness may generally be maximized at disturbance severities that match the predominant historical disturbance regime in a given ecosystem. Studies that examined multiple spatial scales indicate that plant community responses to fire are likely to be scale dependent, suggesting that post‐disturbance monitoring should consider community responses at multiple scales. Synthesis: Our review highlights that consideration of historical disturbance regimes might improve the ability to predict the effects of disturbance on communities. We discuss future research needs; quantitative studies that compare community responses to fire at multiple scales across different historical fire regimes would be particularly useful. Ultimately, consideration of disturbance as a multivariate problem is likely to lead to greater inference than traditional bivariate approaches. [ABSTRACT FROM AUTHOR]

Aim: Recent research has highlighted that the relationship between species interactions and latitude can differ between native and invasive plant taxa, generating biogeographical heterogeneity in community resistance to plant invasions. In the first study with foliar pathogens, we tested whether co‐occurring native and invasive lineages of common reed (Phragmites australis) exhibit non‐parallel latitudinal gradients in foliar fungal communities, pathogen susceptibility and damage, and whether these biogeographical patterns can influence the success of invasion. Location: North America. Time period: 2015–2017. Major taxa studied: Perennial grass P. australis. Methods: We surveyed 35 P. australis field populations, spanning 17° latitude and comprising four phylogeographical lineages, including one endemic to North America and one invasive from Europe. For each population, we quantified the percentage of leaf pathogen damage and cultured fungi from diseased leaves, which we identified using molecular tools. To assess whether latitudinal gradients in pathogen damage had a genetic basis, we inoculated plants from 73 populations with four putative pathogens in a complementary common garden experiment and measured P. australis susceptibility (i.e., diseased leaf area). Results: We isolated 84 foliar fungal taxa. Phragmites australis lineage influenced fungal community composition but not diversity. Despite the invasive European P. australis lineage being the least susceptible to three of the four pathogens tested in the common garden experiment, pathogen damage in the field was similar between native and invasive lineages, providing no evidence that release from foliar pathogens contributes to the success of invasion. Genetically based latitudinal gradients in pathogen susceptibility observed in the common garden were isolate specific and obscured by local environmental conditions in the field, where pathogen damage was threefold higher for northern compared with southern populations, regardless of lineage. Main conclusions: Our results highlight that host plant lineage and genetically based biogeographical gradients strongly influence foliar fungal communities and pathogen susceptibility, but do not translate to patterns of pathogen damage observed in the field. [ABSTRACT FROM AUTHOR]

Fossil rodent middens are powerful tools in paleoecology. In arid parts of western North America, packrat (Neotoma spp.) middens preserve plant and animal remains for tens of thousands of years. Midden contents are so well preserved that fragments of endogenous ancient DNA (aDNA) can be extracted and analyzed across millennia. Here, we explore the use of shotgun metagenomics to study the aDNA obtained from packrat middens up to 32,000 C14 years old. Eleven Illumina HiSeq 2500 libraries were successfully sequenced, and between 0.11% and 6.7% of reads were classified using Centrifuge against the NCBI "nt" database. Eukaryotic taxa identified belonged primarily to vascular plants with smaller proportions mapping to ascomycete fungi, arthropods, chordates, and nematodes. Plant taxonomic diversity in the middens is shown to change through time and tracks changes in assemblages determined by morphological examination of the plant remains. Amplicon sequencing of ITS2 and rbcL provided minimal data for some middens, but failed at amplifying the highly fragmented DNA present in others. With repeated sampling and deep sequencing, analysis of packrat midden aDNA from well‐preserved midden material can provide highly detailed characterizations of past communities of plants, animals, bacteria, and fungi present as trace DNA fossils. The prospects for gaining more paleoecological insights from aDNA for rodent middens will continue to improve with optimization of laboratory methods, decreasing sequencing costs, and increasing computational power. [ABSTRACT FROM AUTHOR]

Aims: Wildfires in dry forest ecosystems in western North America are producing fire effects that are more severe than historical estimates, raising concerns about the resilience of these landscapes to contemporary disturbances. Despite increasing fire activity, relatively little is known about the structure and composition of fire refugia — unburned or low‐severity burned patches where trees survived fire — or the degree to which their understory composition differs from fire‐generated early‐seral forests. Locations: Four recent large fires in dry mixed‐conifer forest in eastern Oregon, USA. Methods: We sampled vegetation and environmental factors in 187 plots (100‐m2) in fire refugia (n = 52) and stand‐replacement patches (SRPs) (n = 135). We used non‐metric multidimensional scaling, indicator species analysis, and randomization tests to compare understory plant communities and diversity in fire refugia and SRPs 12–17 years post‐fire. Results: Understory plant communities in fire refugia and SRPs showed strong compositional affinities, but exhibited shifts in reproductive trait prevalence and differences in landscape‐scale species richness. There were no differences in plot‐scale species richness or the occurrence of two prominent invasive annual grasses (Bromus tectorum, Ventenata dubia). The abundance of common obligate seeding species was similar between plot types, but resprouting and seed‐banking species became substantially more abundant in SRPs. Significantly more plant species occurred only in fire refugia, and significantly fewer in SRPs, than expected by chance. Conclusions: Similarities in understory plant communities between fire refugia and early‐seral forest in SRPs provide evidence for the resilience of historically frequent‐fire forest understory communities to contemporary fire effects. However, fire refugia may serve an ecologically important role as patches with relatively intact forest structure, seed sources that contribute to post‐fire forest recovery, and as reservoirs of species and age structure that may be absent from the higher‐severity burned matrix. [ABSTRACT FROM AUTHOR]

Native pollinators are increasingly needed on conventional farms yet rarely fostered via management. One solution is habitat restoration in marginal areas, but colonization may be constrained if resident pollinator richness is low or if restored areas fail to provide sufficient floral or nesting resources. We quantified restoration outcomes for native bees, and associated resources, on three conventional farms with forb‐grass prairie plantings on marginal areas of varying sizes, in a heavily farmed region of central North America. We tested bee abundance and richness in restored prairie versus the dominant habitats of the region—crops, forest remnants, and edges of fields and roads. Restored prairie supported 2× more species (95 of 119 total species) and 3× more bees (72% of captured individuals) compared to the other cover types. All richness and abundance differences among habitat types were associated with higher floral resources in restored prairie. Thirty percent of the bee species were unique to prairie, consistent with long‐distance dispersal but begging the question of origin given the absence of prairie regionally. Our results suggest that road and field edges may be the source, as these areas had more floral and nesting resources than forest or crop fields combined and supported 55% of all species despite covering only approximately 5% of the sampled farms. Habitat scarcity is not the only constraint on native bees in agricultural landscapes, with increasing concern over disease and chemicals. However, we observed that restored areas on marginal lands of conventional farms can support abundant and species‐rich populations of native bees. [ABSTRACT FROM AUTHOR]

Abstract: The functional composition of plant communities is commonly thought to be determined by contemporary climate. However, if rates of climate‐driven immigration and/or exclusion of species are slow, then contemporary functional composition may be explained by paleoclimate as well as by contemporary climate. We tested this idea by coupling contemporary maps of plant functional trait composition across North and South America to paleoclimate means and temporal variation in temperature and precipitation from the Last Interglacial (120 ka) to the present. Paleoclimate predictors strongly improved prediction of contemporary functional composition compared to contemporary climate predictors, with a stronger influence of temperature in North America (especially during periods of ice melting) and of precipitation in South America (across all times). Thus, climate from tens of thousands of years ago influences contemporary functional composition via slow assemblage dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Cultivation and pasturing, both historically common forms of agriculture in eastern North America, differ in their long‐term environmental legacies. We ask whether successional reassembly of the forest herb community differs between second‐growth stands with contrasting agricultural histories. We predicted that herb communities would diverge through a process of environmental filtering as colonist species responded to the agricultural histories of individual sites and to underlying edaphic gradients. Thirty‐five second‐growth stands were grouped into a replicated chronosequence of formerly cultivated and pastured sites spanning 80 years after canopy closure. Five long‐established stands without signs of agricultural history were included as controls. Herbaceous vegetation and soil and environmental variables were recorded at each site. Forest herb species accumulated through the chronosequence. Community composition changed through successional time, transitioning from open‐forest species to shade‐tolerant perennial herbs, and differed significantly between pastured and cultivated sites. A high degree of similarity among control sites suggests eventual convergence, although chronosequence sites at 80 years had not yet reached the richness and composition observed in the controls. Agricultural practices were initially distinguishable in species richness, evenness, and composition but agricultural influence receded as the stands approached 80 years. Synthesis. Community assembly in post‐agricultural forests appears to be a process of site‐level convergence driven by gradual accumulation of species from the regional species pool, relatively rapid conformity to soil gradients and growth of the forest stand. This result is scale‐dependent; distributions are controlled by topographic filtering at coarser and finer scales. [ABSTRACT FROM AUTHOR]

Aims Apparent competition, in which an invasive plant species promotes herbivory on native plants, has been found in several species-level studies, but has not been investigated at the community level. We compared native and invaded communities to test two hypotheses: that granivory is higher in invaded than native grassland communities, and that granivory is lower for seeds of invasive than native species. Location Northern edge of the Great Plains, northeast Montana, USA and south Saskatchewan, Canada. Methods We studied the widespread invasive grass Agropyron cristatum, which has established on >10 million ha in North America. We compared low-biomass, diverse native grassland and high-biomass, species-poor Agropyron-dominated stands at five sites across 250 km over 2 yr near the northern edge of the Great Plains. Results Granivory in Agropyron stands was nearly double that in native grassland ( P < 0.05), but only in 1 yr (2009). In both years, granivory increased significantly over the growing season and with the cover of forbs. At the two most distal sites, granivory of Agropyron seeds was very similar to the average of all six other plant species examined, suggesting that the invasive species was neither favoured nor disadvantaged by granivory. An exclosure experiment suggested that both birds and small mammals contributed to granivory. As in the community comparison, significant differences among seed species and animal exclosures appeared in 2009 but not 2010. Conclusions Higher granivory in Agropyron stands than native grasslands provided some evidence for apparent competition, but the absence of this effect in 1 yr, combined with the lack of different granivory rates of Agropyron seeds, suggests that granivory-related apparent competition plays a small role in the persistence of this invader. Instead, granivory is more consistently related to time within the growing season and the cover of forbs, and the persistence of Agropyron may be more strongly related to other factors, especially its relatively great root production. [ABSTRACT FROM AUTHOR]

In agricultural catchments, streams are intimately connected with croplands and are exposed to agrochemicals such as fertilisers and herbicides. In North American streams, the effects of nutrient enrichment on riparian and aquatic plant community structure are not well established and the effects of herbicides are largely unknown., We identified the riparian and aquatic plant community at 12 paired stream/river sites (24 in total, Strahler stream order 3-6) located across a large North American agricultural catchment. Field sites ranged in surrounding agricultural land use (2.7-100% annual crops) and in-stream June concentrations of reactive phosphate (6-65 μg L−1 as phosphorus) and nitrate (3-3981 μg L−1 as nitrogen). Atrazine, a herbicide commonly used on corn crops in North America, was widespread throughout the catchment with time-weighted-average concentrations ranging from 4 to 412 ng L−1 over a 56-day period. Atrazine concentrations were >100 ng L−1 at over half the field sites., In total, 285 riparian and aquatic plant taxa were identified. Effects of agrochemicals on descriptors of plant communities were assessed by comparing paired sites surrounded by low or high levels of agriculture and examining changes across the catchment. Agrochemicals had no effect on overall species richness. However, the percentage of non-native species increased across the catchment along a gradient of increasing nitrate. A decline in submerged macrophytes was associated with enrichment of both nitrate and reactive phosphate, whereas no direct effects of atrazine were observed., A floristic quality assessment was used to determine further effects of agrochemicals on riparian and aquatic plant communities. A ranking system, based on native status and tolerance to disturbance, was used to assign coefficient of conservation values to each species. Floristic quality was subsequently calculated as a function of species richness and the average coefficient of conservation value at each site. Overall floristic quality decreased as nitrate increased. Species positively associated with nitrate were typically fast-growing, weedy, riparian species, whereas species negatively associated with nitrate were characteristic of less disturbed areas and represented a range of growth forms., We conclude that nutrient enrichment, especially of nitrate, has multiple negative effects on riparian and aquatic plant communities that override effects of the herbicide atrazine. Our results highlight the need to reduce inputs of agrochemicals to streams and to regulate nitrogen in addition to phosphorus. [ABSTRACT FROM AUTHOR]

Question In fire-prone boreal forests, to what extent does fire severity influence understorey plant community assembly? What are the abiotic and biotic factors controlling understorey community regeneration at regional, landscape and local scales? Location Black spruce-dominated boreal forest in eastern Canada. Methods A taxonomic and a trait-based approach were combined to evaluate the relative influence of habitat characteristics, burn severity and biotic processes on understorey regeneration at multiple spatial scales. Sampling of understorey vegetation cover was carried out in 133 recently burned plots located in 14 different fires across a 600-km transect. The spatial hierarchy for sampling consisted of five fire regime zones (regional scale), two to four fires within each zone (landscape) and two to four toposequences within each fire (local). The environmental control of fire severity and habitat characteristics on understorey regeneration was assessed using a canonical redundancy analysis ( RDA) and variation partitioning. We investigated environmental and biotic filters of species traits at different scales by modelling trait-spatial assemblages with Moran eigen vector maps ( MEMs). Results In spite of the large variability of environmental conditions covered by our sampling design, low depths of burn were measured in the large majority of the studied sites. Incomplete consumption of the forest floor is frequently observed in eastern boreal forests characterized by long fire cycles. In situ biological legacies persisted through the low-severity fires, which conserved the pre-fire relationships between plant communities and their environment. As a result, fire severity was neither the unique nor the dominant control on post-fire regeneration. Habitat characteristics explained a three times higher proportion of variation in species composition. Biotic controls on trait assemblage increased at the two finer scales. Conclusions Severity alone cannot predict understorey vegetation assembly at different scales in the low-severity fire regime characteristic of the eastern North American boreal forest. [ABSTRACT FROM AUTHOR]

Changes in plant community composition may be driven partly by the traits of dominant species during succession. In degraded northern China grasslands, plant community composition has changed remarkably and previous studies have mostly focused on the effects of anthropogenic activities, ignoring the role of interspecific interactions. We hypothesized that Potentilla acaulis, a dominant plant in heavily degraded steppe landscapes, inhibits co-occurring plant species by exuding allelopathic exudates that are inhibitory to establishing seedlings. Field vegetation surveys showed that mean heights and importance values of Stipa krylovii and Leymus chinensis were significantly lower in patches dominated by P. acaulis compared with patches dominated by S. krylovii. In germination experiments, P. acaulis extracts had significant allelopathic effects on three grass species ( S. krylovii, Artemisia frigida, and L. chinensis) common in northern China grasslands. Allelopathic effects were a factor of exudate source, exudate concentration, and target species. Shoot growth of L. chinensis and A. frigida, extracts showed a 'low-promotion and high-inhibition' effect, wherein low levels of exudate had a growth-promoting effect, but higher concentrations had an increasingly inhibitory effect. S. krylovii was the most sensitive target species, and both its shoot and radicle growth were significantly reduced in the presence of P. acaulis. As with the other two targets, the magnitude of inhibition increased with increasing exudate concentration. Ecologically, this study suggests that allelopathy may contribute to the dominance of P. acaulis in degraded grasslands, which has important implications for recovery of other native plants in these degraded grasslands. The specific mechanism demands further investigation. [ABSTRACT FROM AUTHOR]

Questions How has plant species richness changed over two decades in one of the most species-rich savannas in North America? Is an altered disturbance regime, environmental stress, or both, driving these changes? In what ways can observations in this savanna inform management of other species-rich plant communities? Location Longleaf pine savannas in southeast North Carolina, USA. Methods In 2011-2013, we re-surveyed permanent plots established in the 1980s and 1990s in a longleaf pine ( Pinus palustris) savanna in North Carolina to quantify changes in species richness at multiple spatial scales following 15 yr of reduced fire frequency plus periodic drought. For comparison, we re-sampled other longleaf pine savannas in the region that had not experienced reduced fire frequency, but had experienced similar drought. In addition, we identified which types of species were lost and gained, and summarized changes in species frequency by growth form, plant height, and habitat affinity. Results We detected substantial declines in small-scale species richness and species frequency from the 1980s to 2011, representing a loss of 33% to 41% of the flora, depending on the spatial scale. Small herbaceous species had become particularly scarce. Additional re-sampling in the wetter years of 2012 and 2013 after consecutive years of fire revealed that species richness had increased slightly from 2011, but was still considerably lower than that in the 1980s. Other savannas did not exhibit such dramatic declines in species richness, suggesting reduced fire frequency in addition to drought contributed to species loss in Big Island Savanna over time. Conclusions Our work suggests that nearly annual fire is necessary for the maintenance of high plant species richness in mesic longleaf pine savannas, and even a modest reduction in fire frequency can have dramatic negative impacts. This study also suggests that drought is an important factor structuring grassland ecosystems in the southeastern US, despite relatively high regional precipitation. We believe these findings can be generalized to other species-rich grasslands that are sensitive to changes in disturbance regimes and may require frequent disturbance to maintain plant species richness. [ABSTRACT FROM AUTHOR]

Aim We aimed to quantify the relative contributions of trait-based selection and the flow of individuals across space created by differences in species abundance, i.e. mass effects, in determining local-scale species relative abundance ( SRA) at 0.07 ha, 1° grid cell and subregion grains. Location The eastern USA. Methods We coupled a maximum entropy model ( MaxEnt) with nine species-specific plant traits and a continental-scale forest inventory dataset to perform our analyses. Mass effects were estimated using the next grain size up as the metacommunity (or the eastern USA at the subregion grain, and also at the 1° grid cell grain in a fourth analysis). Permutation tests were conducted to test the significance of trait constraints. The Kullback- Leibler divergence index was used to decompose the information content in each assemblage SRA. Results Trait constraints were significant in predicting community structures at coarse scales, but were largely not significant at fine or medium scales. At the 0.07 ha grain little of the variation in local SRA can be explained by either trait constraints or a regional SRA. At the 1° grain c. 61% of the variation could be accounted for by a regional SRA represented by subregions. At the subregion grain c. 74% of the variation could be accounted for by trait constraints and the SRA of the entire study area. Main conclusions Our results suggest that the relative importance of community assembly processes is scale dependent. Estimated mass effects predominated at small spatial scales where environmental gradients were weak. Trait-based selection was hard to detect at small scales and was strongest at large scales where environmental gradients are stronger. The fact that, at all scales, mass effects accounted for more variation in assemblage SRA than trait-based selection in our analyses suggests that regional processes are important in determining community structures more locally. [ABSTRACT FROM AUTHOR]

Projecting the future composition and function of communities is a major challenge, and there is an urgent need to develop, improve, and test the predictive capacity of ecological models under different climate states. We tested the effect of climate on spatial patterns of plant community composition over the past 21 000 yr, focusing on whether the spatial relationships between environmental distance and compositional dissimilarity are stable over time. We used a network of fossil-pollen sites in eastern North America, combined with paleoclimate simulations from the Last Glacial Maximum (LGM; 21 000 calibrated years before present, 21 kyr BP) to the present. We modeled relationships between climate, geography, and compositional dissimilarity at 1 kyr periods using generalized dissimilarity modeling (GDM) and determined the strongest predictors of compositional dissimilarity. We assessed the performance of models calibrated for one time period (e.g. 14 kyr BP) in predicting patterns in the same period as well as at other times (e.g. 12 kyr BP), and tested whether predictive performance was related to the magnitude of climate change between the calibration and prediction time periods. Finally, we examined whether pooling data from multiple time periods improved predictive performance. Models explained 32 to 51% of compositional dissimilarity between locations within any single time period. The best set of predictors changed across time, with summer temperature and geographic distance the strongest predictors of compositional dissimilarity for most time periods. Models built for one time period explained turnover during nearby time periods relatively well, but performance decayed across time and with increasing climate change. Results were similar regardless of whether models were projected forward or backward through time, and did not improve when data were pooled across time. GDM predicts well the spatial patterns of past compositional dissimilarity and holds promise for modeling the drivers of compositional dissimilarity across space and time. However, the modeled relationships between compositional turnover and environmental distance are non-stationary, so caution is needed when predicting across periods of significant climatic change. [ABSTRACT FROM AUTHOR]

Biotic resistance, the ability of species in a community to limit invasion, is central to our understanding of how communities at risk of invasion assemble after disturbances, but it has yet to translate into guiding principles for the restoration of invasion-resistant plant communities. We combined experimental, functional, and modelling approaches to investigate processes of community assembly contributing to biotic resistance to an introduced lineage of Phragmites australis, a model invasive species in North America. We hypothesized that (i) functional group identity would be a good predictor of biotic resistance to P. australis, while species identity effect would be redundant within functional group (ii) mixtures of species would be more invasion resistant than monocultures., We classified 36 resident wetland plants into four functional groups based on eight functional traits. We conducted two competition experiments based on the additive competition design with P. australis and monocultures or mixtures of wetland plants. As an indicator of biotic resistance, we calculated a relative competition index ( RCIavg) based on the average performance of P. australis in competition treatment compared with control. To explain diversity effect further, we partitioned it into selection effect and complementarity effect and tested several diversity-interaction models., In monoculture treatments, RCIavg of wetland plants was significantly different among functional groups, but not within each functional group. We found the highest RCIavg for fast-growing annuals, suggesting priority effect., RCIavg of wetland plants was significantly greater in mixture than in monoculture mainly due to complementarity-diversity effect among functional groups. In diversity-interaction models, species interaction patterns in mixtures were described best by interactions between functional groups when fitted to RCIavg or biomass, implying niche partitioning., Synthesis. Functional group identity and diversity of resident plant communities are good indicators of biotic resistance to invasion by introduced Phragmites australis, suggesting niche pre-emption (priority effect) and niche partitioning (diversity effect) as underlying mechanisms. Guiding principles to understand and/or manage biological invasion could emerge from advances in community theory and the use of a functional framework. Targeting widely distributed invasive plants in different contexts and scaling up to field situations will facilitate generalization. [ABSTRACT FROM AUTHOR]

1. Land-use change is considered one of the most radical and extensive disturbances that have influenced plant distributions and diversity patterns in forest understorey communities in much of Europe and eastern North America. In forests growing on former agricultural land, local species diversity and community differentiation among sites are generally reduced compared with ancient forests (i.e. forests with no historical record of agriculture). Yet, no study has determined how the compositional differences created by former land-use change over time as the forest sites recover from former agricultural use. 2. Here, we resurveyed 78 vegetation plots (half of the plots in ancient and half in post-agricultural forest) to demonstrate how three decades of forest development have changed the compositional differences between post-agricultural and ancient forest sites. The impact of land-use history and survey date was tested on two measures of species diversity and two measure of community divergence. 3. The data indicate that the imprint of former agricultural land use persisted over time, yet not through compositional stability. Parallel and strong vegetation shifts occurred in both ancient and post-agricultural forest: the species diversity decreased and local species cover strongly diverged, which indicates community drift. The observed understorey changes did thus not support the commonly accepted model of community development in post-agricultural forests, i.e. the diversity did not increase and the vegetation did not become more similar to the ancient forest vegetation over time. The changes in species composition were associated with an increase of common, competitive species at the expense of ancient forest indicator species. The source populations of ancient forest species have been gradually depleted, so the recovery of post-agricultural forests becomes even more precarious. 4. Synthesis. While land-use history is likely to persist as the primary predictor of local species diversity and community divergence, other environmental drivers may additionally structure forest understorey communities and lead to biotic impoverishment and pervasive species reordering on the time scale of only decades. [ABSTRACT FROM AUTHOR]

•Despite a growing awareness of the global reach of ectomycorrhizal (EM) fungal introductions, little is known about the fate of introduced EM fungi in novel ranges. •Using herbarium specimens, species distribution models, and field collections of sporocarps, root tips and extramatrical mycelia, we assessed the distribution and abundance of the European species Amanita phalloides in North America. •There are two distinct ranges of the fungus, one along the West Coast (California to British Columbia) and the second on the East Coast (Maryland to Maine). As predicted by a species distribution model, the West Coast range is larger. Amanita phalloides is more frequently found in native forests on the West Coast than on the East Coast. At Point Reyes Peninsula in California, A. phalloides dominates community sporocarp biomass, and is frequent as root tips. In individual soil cores at Point Reyes, root tips of A. phalloides make up 50% of total root tip biomass. Hyphae of A. phalloides are frequent, but make up only 2% of total hyphal biomass. •The contrasting patterns of the distribution and abundance of A. phalloides on the East and West Coasts of North America may influence both its future spread and its impacts. [ABSTRACT FROM AUTHOR]

Identification of factors that drive changes in plant community structure and contribute to decline and endangerment of native plant species is essential to the development of appropriate management strategies. Introduced species are assumed to be driving causes of shifts in native plant communities, but unequivocal evidence supporting this view is frequently lacking. We measured native vegetation, non-native earthworm biomass, and leaf-litter volume in 15 forests in the presence and absence of 3 non-native plant species (Microstegium vimineum, Alliaria petiolata, Berberis thunbergii ) to assess the general impact of non-native plant and earthworm invasions on native plant communities in northeastern United States. Non-native plant cover was positively correlated with total native plant cover and non-native earthworm biomass. Earthworm biomass was negatively associated with cover of native woody and most herbaceous plants and with litter volume. Graminoid cover was positively associated with non-native earthworm biomass and non-native plant cover. These earthworm-associated responses were detected at all sites despite differences in earthworm species and abundance, composition of the native plant community, identity of invasive plant species, and geographic region. These patterns suggest earthworm invasion, rather than non-native plant invasion, is the driving force behind changes in forest plant communities in northeastern North America, including declines in native plant species, and earthworm invasions appear to facilitate plant invasions in these forests. Thus, a focus on management of invasive plant species may be insufficient to protect northeastern forest understory species. [ABSTRACT FROM AUTHOR]

1. Tamarisk species ( Tamarix ramosissima Ledeb., T. chinensis Lour., T. gallica L. and hybrids) have invaded riparian areas throughout western North America, resulting in expansive control efforts. Tamarisk is a relatively recent addition to North American plant communities, and competitive and successional processes are still developing. Box elder ( Acer negundo L. var. interius (Britt.) Sarg.) is a native competitor found in canyons throughout western North America. We investigated the establishment chronology, competition and comparative shade tolerances of tamarisk and box elder to determine the superior competitor and to predict successional trajectories in mixed stands. 2. Competition was studied through neighbourhood analysis, and successional trends were analysed through dendrochronology in the canyons of Dinosaur National Monument, CO, USA. The shade tolerance of mature tamarisk was studied by enclosing individual plants in shade cloth for two growing seasons. The comparative shade tolerances of juvenile tamarisk and box elder were studied using five levels of shading in a glasshouse experiment. 3. Box elder and tamarisk established concurrently, or tamarisk establishment preceded box elder establishment. Box elder was the superior competitor; the presence of canopy box elders within 1 and 2 m was significantly related to tamarisk mortality but not box elder mortality. The presence of canopy tamarisk trees was not related to box elder or tamarisk mortality. 4. In the field-based experiment, mature tamarisks were killed when subjected to one to two growing seasons of 98% shade. In the greenhouse-based experiment, box elder had superior shade tolerance to tamarisk, maintained positive growth and survived under higher shade than tamarisk. 5. Synthesis and applications. Box elder is a superior competitor to tamarisk, and is capable of establishing under dense tamarisk canopies, overtopping and eventually killing tamarisk. Superior shade tolerance appears to be the mechanism for the successional replacement of tamarisk by box elder. The manipulation of competitive and successional processes through the promotion of box elder and other native tree establishment is suggested as a means of tamarisk control to complement traditional control techniques. [ABSTRACT FROM AUTHOR]

Aim To estimate the effects of full-glacial atmospheric CO2 concentrations and climate upon leaf area index (LAI), using both global vegetation models and palaeoecological data. Prior simulations indicate lowered LAIs at the Last Glacial Maximum (LGM), but this is the first attempt to corroborate predictions against observations. Location Eastern North America and eastern Beringia. Methods Using a dense surface pollen data set and remotely sensed LAIs from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument, we evaluate the ability of analogue-based techniques to reconstruct modern LAIs from pollen data. We then apply analogue techniques to LGM pollen records, calculate the ratio of LGM to modern LAIs (RLAI) and compare reconstructed RLAIs to RLAIs simulated by BIOME4. Sensitivity experiments with BIOME4 distinguish the effects of CO2 and climate on glacial LAIs. Results Modern LAIs are skilfully predicted ( r2= 0.83). Data and BIOME4 indicate that LAIs at the LGM were up to 12% lower than modern values in eastern North America and 60–94% lower in Beringia. In eastern North America, LGM climates partially counteracted CO2-driven decreases in LAI, while in Beringia both contributed to lowered LAIs. Main conclusions In both regions climate is the primary driver of LGM LAIs. The decline in eastern North America LAIs is smaller than previously reported, so regional vegetation feedbacks to LGM climate may have been less significant than previously supposed. CO2 exerts both physiological and community effects upon LAI, by regulating resource availability for leaf production and by influencing the competitive balance among species and hence the composition and structure of plant communities. Pollen-based reconstructions using analogue methods do not incorporate the physiological effect and so are upper estimates of full-glacial LAIs. BIOME4 sensitivity experiments indicate that the community and physiological effects together caused 10% to 20% decrease in LAIs at the LGM, so simulated RLAIs that are 80–100% of reconstructed RLAIs are regarded as consistent with data. [ABSTRACT FROM AUTHOR]

To determine if non-native plant species are homogenizing species composition among widely dispersed plant communities. Twenty localities in North America. Species lists among localities were compared to measure the influence of non-native species richness at each locality on the Jaccard Index (JI) of similarity between localities. After removing the effects of distance, because shared native species decreased with distance, three (nonexclusive) lines of evidence indicate that non-native species promote homogenization. First, pairs of sites with a high combined total of non-native species tend to have higher similarity than those with a low total of non-natives. Second, for a given distance, more non-native than native species tended to be shared among localities. Third, whereas most of the site comparisons with high total non-native richness have a non-native/native JI ratio greater than 1 (often much greater), only half of the comparisons with low total non-native richness have a ratio greater than one. These findings provide quantitative support for the widely held, but rarely tested, notion that non-native species tend to homogenize biological communities because they are more commonly shared among communities. Such testing is important as non-native species could theoretically have no impact or even reduce homogenization among communities, if non-native colonizers consist of different species pools. [ABSTRACT FROM AUTHOR]

Summary 1.Nutrient enrichment may adversely impact plant species richness in wetlands and enhance their susceptibility to colonization and dominance by invasive species. For North American prairie wetlands, enrichment by nitrate-N (NO3 -N) from agricultural runoff is thought to contribute to the increasing colonization and dominance of Phalaris arundinacea (reed canary grass), especially during restoration. If true, P. arundinacea might compromise the re-establishment of sedge meadow vegetation on sites reflooded with agricultural drainage water. 2.We tested this hypothesis using a fertilization experiment in wetlands with controlled hydrology. A community mixture comprising 11 species from native sedge meadow was seeded in mesocosms and grown under one of three NO3 -N levels (0 g m-2 year-1 , 12 g m-2 year-1 , 48 g m-2 year-1 ) with or without P. arundinacea. Above- and below-ground biomass were measured after two growing seasons to assess the response of vegetation to NO3 -N and P. arundinacea treatments. 3.The total shoot biomass of the native community was suppressed in the presence of P. arundinacea at all NO3 -N levels, but shoot suppression was significantly greater at the highest NO3 -N dose level (48 g m-2 ). Shoot growth of the native community was reduced by nearly one-half under these conditions. 4.The total root biomass of the community was also suppressed by P. arundinacea when no NO3 -N was added. 5.As NO3 -N increased, the relative abundance (shoot biomass) of native graminoids declined while native forbs increased in communities with and without Phalaris. The most common graminoid, Glyceria grandis , was suppressed by P. arundinacea at all levels, with suppression enhanced at the 48 g m-2 NO3 -N level. Three other species were suppressed at the highest NO3 -N... [ABSTRACT FROM AUTHOR]

AbstractAimMany studies have shown that the pollen record can be used to distinguish grasslands from other vegetation types at the biome level, but few have attempted to use pollen to distinguish between specific prairie types. This study was undertaken to determine whether the tallgrass, mixed-grass, shortgrass, and desert grasslands of North America have unique pollen signatures that can be used to distinguish between grasslands at the community-scale, rather than at the scale of the biome. LocationData was collected from the southern North American grasslands of Oklahoma, Texas, and New Mexico. MethodsHigh resolution, annual pollen-influx data gathered in Tauber pollen traps were analyzed using cluster analysis to summarize the pollen signature from each trap locality and to catagorize the samples into discrete grassland groups. ResultsBased on the results of the cluster analysis, each grassland produces a distinctive pollen signature that can be used to distinguish between grassland types. In addition, pollen influx is shown to be closely correlated with annual precipitation. Main conclusionsThe ability to distinguish between grassland types and to relate annual influx to annual precipitation has important implications for understanding the evolution of grasslands during the Holocene, for palaeoclimatic studies, and for monitoring ecosystem changes in the present-day grasslands. [ABSTRACT FROM AUTHOR]

Sensitivity of plant species to individual arbuscular mycorrhizal (AM) fungal species is of primary importance to understanding the role of AM fungal diversity and composition in plant ecology. Currently, we do not have a predictive framework for understanding which plant species are sensitive to different AM fungal species. In two greenhouse studies, we tested for differences in plant sensitivity to different AM fungal species and mycorrhizal responsiveness across 17 grassland plant species of North America that varied in successional stage, native status, and plant family by growing plants with different AM fungal treatments including eight single AM fungal isolates, diverse mixtures of AM fungi, and non‐inoculated controls. We found that late successional grassland plant species were highly responsive to AM fungi and exhibited stronger sensitivity in their response to individual AM fungal taxa compared to nonnative or early successional native grassland plant species. We confirmed these results using a meta‐analysis that included 13 experiments, 37 plant species, and 40 fungal isolates (from nine publications and two greenhouse experiments presented herein). Mycorrhizal responsiveness and sensitivity of response (i.e., variation in plant biomass response to different AM fungal taxa) did not differ by the source of fungal inocula (i.e., local or not local) or plant family. Sensitivity of plant response to AM fungal species was consistently correlated with the average mycorrhizal response of that plant species. This study identifies that AM fungal identity is more important to the growth of late successional plant species than early successional or nonnative plant species, thereby predicting that AM fungal composition will be more important to plant community dynamics in late successional communities than in early successional or invaded plant communities. [ABSTRACT FROM AUTHOR]

In drylands, the coexistence of grasses and woody plants has been attributed to soil‐water resource partitioning. Soil texture and precipitation seasonality can influence the amount and distribution of water in the soil, and their interaction may play an important role in determining the relative importance of grasses and woody plants. We investigated the influence of this interaction on plant functional types across a broad range of precipitation regimes and soil textures in western North America by analyzing plant‐cover data collected at 2,084 plots that included the widespread shrub big sagebrush (Artemisia tridentata Nutt.). We characterized how the significance of the inverse‐texture effect varies across soil conditions by quantifying relationships between precipitation and foliar cover on finer‐ vs. coarser‐textured soils across a range of potential texture divisions represented by sand content. We found evidence of the inverse‐texture effect for every plant functional type (except for cheatgrass) that we examined with at least one component of precipitation (annual, warm, or cold season), and provide the first evidence for this effect in locations with cold‐season‐dominated precipitation regimes. The texture and precipitation combinations that exhibited the inverse‐texture effect varied with plant functional type, presumably because of effects of soil texture on water availability at different soil depths with season. Furthermore, we found an inverse‐texture effect that was remarkably similar for shrub cover with cold‐season precipitation and grass cover with warm‐season precipitation. These results provide new insight into how the inverse‐texture effect interacts with precipitation seasonality to influence plant functional type composition in drylands, and further suggest that quantifying the soil‐texture division at which the inverse‐texture effect is relevant under a given set of environmental conditions may provide support for the effect across dryland plant communities. [ABSTRACT FROM AUTHOR]