A functional trait perspective on plant invasion

Global environmental change will affect non-native plant invasions, with profound potential impacts on native plant populations, communities and ecosystems. In this context, we review plant functional traits, particularly those that drive invader abundance (invasiveness) and impacts, as well as the integration of these traitsacross multiple ecological scales, and as a basis for restoration and management.We review the concepts and terminology surrounding functional traits and how functional traits influence processes at the individual level. We explore how phenotypic plasticity may lead to rapid evolution of novel traits facilitating invasiveness in changing environments and then oscale up\u27 to evaluate the relative importance of demographic traits and their links to invasion rates. We then suggest a functional trait framework for assessing per capita effects and, ultimately, impacts of invasive plants on plant communities and ecosystems. Lastly, we focus on the role of functional trait-based approaches in invasive species management and restoration in the context of rapid, global environmental change.To understand how the abundance and impacts of invasive plants will respond to rapid environmental changes it is essential to link trait-based responses of invaders to changes in community and ecosystem properties. To do so requires a comprehensive effort that considers dynamic environmental controls and a targeted approach to understand key functional traits driving both invader abundance and impacts. If we are to predict future invasions, manage those at hand and use restoration technology to mitigate invasive species impacts, future research must focus on functional traits that promote invasiveness and invader impacts under changing conditions, and integrate major factors driving invasions from individual to ecosystem levels

Non-Additive Effects on Decomposition from Mixing Litter of the Invasive Mikania micrantha H.B.K. with Native Plants

A common hypothesis to explain the effect of litter mixing is based on the difference in litter N content between mixed species. Although many studies have shown that litter of invasive non-native plants typically has higher N content than that of native plants in the communities they invade, there has been surprisingly little study of mixing effects during plant invasions. We address this question in south China where Mikania micrantha H.B.K., a non-native vine, with high litter N content, has invaded many forested ecosystems. We were specifically interested in whether this invader accelerated decomposition and how the strength of the litter mixing effect changes with the degree of invasion and over time during litter decomposition. Using litterbags, we evaluated the effect of mixing litter of M. micrantha with the litter of 7 native resident plants, at 3 ratios: M1 (1:4, = exotic:native litter), M2 (1:1) and M3 (4:1, = exotic:native litter) over three incubation periods. We compared mixed litter with unmixed litter of the native species to identify if a non-additive effect of mixing litter existed. We found that there were positive significant non-additive effects of litter mixing on both mass loss and nutrient release. These effects changed with native species identity, mixture ratio and decay times. Overall the greatest accelerations of mixture decay and N release tended to be in the highest degree of invasion (mix ratio M3) and during the middle and final measured stages of decomposition. Contrary to expectations, the initial difference in litter N did not explain species differences in the effect of mixing but overall it appears that invasion by M. micrantha is accelerating the decomposition of native species litter. This effect on a fundamental ecosystem process could contribute to higher rates of nutrient turnover in invaded ecosystems. © 2013 Chen et al

Resilience to Stress and Disturbance, and Resistance to Bromus tectorum L. Invasion in Cold Desert Shrublands of Western North America

Alien grass invasions in arid and semi-arid ecosystems are resulting in grass–fire cycles and ecosystem-level transformations that severely diminish ecosystem services. Our capacity to address the rapid and complex changes occurring in these ecosystems can be enhanced by developing an understanding of the environmental factors and ecosystem attributes that determine resilience of native ecosystems to stress and disturbance, and resistance to invasion. Cold desert shrublands occur over strong environmental gradients and exhibit significant differences in resilience and resistance. They provide an excellent opportunity to increase our understanding of these concepts. Herein, we examine a series of linked questions about (a) ecosystem attributes that determine resilience and resistance along environmental gradients, (b) effects of disturbances like livestock grazing and altered fire regimes and of stressors like rapid climate change, rising CO2, and N deposition on resilience and resistance, and (c) interacting effects of resilience and resistance on ecosystems with different environmental conditions. We conclude by providing strategies for the use of resilience and resistance concepts in a management context. At ecological site scales, state and transition models are used to illustrate how differences in resilience and resistance influence potential alternative vegetation states, transitions among states, and thresholds. At landscape scales management strategies based on resilience and resistance—protection, prevention, restoration, and monitoring and adaptive management—are used to determine priority management areas and appropriate actions

Integrated Assessment of Biological Invasions

As the main witnesses of the ecological and economic impacts of invasions on ecosystems around the world, ecologists seek to provide the relevant science that informs managers about the potential for invasion of specific organisms in their region(s) of interest. Yet, the assorted literature that could inform such forecasts is rarely integrated to do so, and further, the diverse nature of the data available complicates synthesis and quantitative prediction. Here we present a set of analytical tools for synthesizing different levels of distributional and/or demographic data to produce meaningful assessments of invasion potential that can guide management at multiple phases of ongoing invasions, from dispersal to colonization to proliferation. We illustrate the utility of data-synthesis and data-model assimilation approaches with case studies of three well-known invasive species—a vine, a marine mussel, and a freshwater crayfish—under current and projected future climatic conditions. Results from the integrated assessments reflect the complexity of the invasion process and show that the most relevant climatic variables can have contrasting effects or operate at different intensities across habitat types. As a consequence, for two of the study species climate trends will increase the likelihood of invasion in some habitats and decrease it in others. Our results identified and quantified both bottlenecks and windows of opportunity for invasion, mainly related to the role of human uses of the landscape or to disruption of the flow of resources. The approach we describe has a high potential to enhance model realism, explanatory insight, and predictive capability, generating information that can inform management decisions and optimize phase-specific prevention and control efforts for a wide range of biological invasions

Will Extreme Climatic Events Facilitate Biological Invasions?

Extreme climatic events (ECEs) – such as unusual heat waves, hurricanes, floods, and droughts – can dramatically affect ecological and evolutionary processes, and these events are projected to become more frequent and more intense with ongoing climate change. However, the implications of ECEs for biological invasions remain poorly understood. Using concepts and empirical evidence from invasion ecology, we identify mechanisms by which ECEs may influence the invasion process, from initial introduction through establishment and spread. We summarize how ECEs can enhance invasions by promoting the transport of propagules into new regions, by decreasing the resistance of native communities to establishment, and also sometimes by putting existing non-native species at a competitive disadvantage. Finally, we outline priority research areas and management approaches for anticipating future risks of unwanted invasions following ECEs. Given predicted increases in both ECE occurrence and rates of species introductions around the globe during the coming decades, there is an urgent need to understand how these two processes interact to affect ecosystem composition and functioning

A REGIONAL EXPERIMENT TO EVALUATE EFFECTS OF FIRE AND FIRE SURROGATE TREATMENTS IN THE SAGEBRUSH BIOME

SageSTEP is a comprehensive regional experiment that provides critical information to managers faced with a sagebrush steppe ecosystem that is increasingly at risk from wildfire, invasive plants, and climate change. The experiment provides managers with information that can be used to restore ecological communities across the 100+ million acres of the sagebrush biome. It is designed to match the temporal and spatial scales at which managers operate, is intended to reduce management risk and uncertainty of catastrophic wildfire to the greatest degree possible, and provides managers with information that allows them to better understand tradeoffs inherent in the choice of management alternatives. The project has several features that make it ideal for testing hypotheses from state‐andtransition theory, and for discovering information that can be directly applied in a management context ‐‐ it is long‐term, experimental, multisite, multivariate, and treatments are applied across condition gradients, allowing for potential identification of biotic thresholds. The project is designed to distinguish communities that have conditions that will allow them to recover on their own following fuel or restoration treatments, versus communities that have crossed biotic thresholds, and will therefore require more expensive active restoration. SageSTEP is designed as a long‐term study, such that measurements are planned for at least 10 years after treatment implementation, or through the 2018 field season. This final report therefore describes the short‐term effects of treatments, 2‐4 years after treatment implementation., or through the 2010 field season. The Joint Fire Science Program generously funded SageSTEP for its first six years, and this funding was crucial for building an infrastructure that has now set the stage for an unprecedented long‐term study that will provide badly needed information on sagebrush steppe restoration and fuel treatment effectiveness. The infrastructure we’ve built consists of the following eight features: 1. A network of 18 sites distributed across the Great Basin, Snake River Basin, and Columbia Basin, 11 sites in a replicated woodland experiment, and 7 sites in a replicated sage‐cheat experiment (Figure 1). Each site is equivalent to a statistical block consisting of an unmanipulated control, and a set of fire and fire surrogate treatments. 2. A network of weather and soil moisture stations distributed along with the sites, that provides information on inter‐annual and geographic variation in moisture and temperature, and that is being used to interpret patterns of ecological response. 3. A small by efficient staff, consisting of scientists and technicians, responsible for continued monitoring of ecological variables through time, and maintenance of the projects’ infrastructure. 4. A funding stream from several agency sources, with current resources adequate to run the project for at least three more years, and with agreements in place to fund the project through fiscal year 2015. 5. A web of partnerships among managers, scientists, students, stakeholders, and policymakers that has worked together to design the study, implement the treatments, and learn about how sagebrush steppe system respond to alternative restoration treatments. 6. A highly effective and influential outreach program, anchored by a popular website, designed to interpret and deliver scientific information collected by SageSTEP scientists, and to distribute other relevant information originating from outside the project. 7. An on‐line database, called the SageSTEP Data Store, that offers fully proofed and validated data to analysts working within SageSTEP, and which will eventually provide the same information to other interested users. 8. The Great Basin NEON Site, NSF’s atmospheric sampling station that will soon be built at the SageSTEP Onaqui site. This link with NSF provides SageSTEP with leverage for established additional vegetation and soil monitoring facilities at Onaqui. Over the past three years, since post‐treatment data collection commenced, SageSTEP has produced a considerable amount of information, most of it now published in a total of 32 scientific papers. Key outreach products include: ● Active web site (sagestep.org), anchoring a comprehensive outreach program ● User\u27s Guides for Western Juniper & Pinyon‐Juniper woodlands ● Two Fuel Guides, one each for pre‐treatment and post‐treatment conditions ● 15 quarterly newsletters ● Six manager workshops ● 11 tours or field trips ● Three national conference symposia, consisting of 24 papers (2 symposia planned) ● 57 contributed papers at conferences ● Seven Master’s Theses and two Ph.D. Dissertations ● 15 papers published in proceedings or reports ● Ten papers published in peer‐reviewed journals (17 papers currently in review

Nitrogen Increases Early-Stage and Slows Late-Stage Decomposition Across Diverse Grasslands

To evaluate how increased anthropogenic nutrient inputs alter carbon cycling in grasslands, we conducted a litter decomposition study across 20 temperate grasslands on three continents within the Nutrient Network, a globally distributed nutrient enrichment experiment We determined the effects of addition of experimental nitrogen (N), phosphorus (P) and potassium plus micronutrient (Kμ) on decomposition of a common tree leaf litter in a long-term study (maximum of 7 years; exact deployment period varied across sites). The use of higher order decomposition models allowed us to distinguish between the effects of nutrients on early- versus late-stage decomposition. Across continents, the addition of N (but not other nutrients) accelerated early-stage decomposition and slowed late-stage decomposition, increasing the slowly decomposing fraction by 28% and the overall litter mean residence time by 58%. Synthesis. Using a novel, long-term cross-site experiment, we found widespread evidence that N enhances the early stages of above-ground plant litter decomposition across diverse and widespread temperate grassland sites but slows late-stage decomposition. These findings were corroborated by fitting the data to multiple decomposition models and have implications for N effects on soil organic matter formation. For example, following N enrichment, increased microbial processing of litter substrates early in decomposition could promote the production and transfer of low molecular weight compounds to soils and potentially enhance the stabilization of mineral-associated organic matter. By contrast, by slowing late-stage decomposition, N enrichment could promote particulate organic matter (POM) accumulation. Such hypotheses deserve further testing

Understory Succession Following a Dieback of \u3ci\u3eMyrica faya\u3c/i\u3e in Hawai’i Volcanoes National Park

Studies of invasion by the introduced nitrogen-fixing tree Myrica faya Aiton in Hawai\u27i Volcanoes National Park have led to predictions that the nitrogen-rich soil M. faya creates will promote invasion by nonindigenous plant species. An insect-caused dieback of M. faya that began in the late 1980s provides an opportunity to test this hypothesis. We compared· percentage cover and density of all plant species under live and dead M. faya, as well as total nitrogen in soil and plant tissue. Mean percentage cover of four common species increased significantly, and no species decreased in cover after dieback. Cover of native shrubs and herbs increased from 4.8 to 15.2%, largely due to the spread of Carex wahuensis C.A. Mey, and introduced grasses increased from 2.3 to 14.1%. Density of native shrubs did not differ beneath live and dead M. faya, but immature introduced grass individuals were significantly more numerous beneath dead M. faya. We found no differences in total nitrogen in soil or plant tissue collected beneath live versus dead M. faya. Beneath dead M. faya, cover of C. wahuensis increased with total soil N, and introduced grass cover decreased. This surprising result may be the legacy of shading effects from the live M. faya canopies, for which total soil N may be an indicator. Success of grass seedlings compared with failure of native shrubs to recruit from seed suggests that dieback promotes nonnative grass species. Replacement of M. faya with introduced grasses may greatly increase fire risk

SHRUB FACILITATION OF COAST LIVE OAK ESTABLISHMENT IN CENTRAL CALIFORNIA

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Arbuscular mycorrhizal assemblages in native plant roots change in the presence of invasive exotic grasses

Plant invasions have the potential to significantly alter soil microbial communities, given their often considerable aboveground effects. We examined how plant invasions altered the arbuscular mycorrhizal fungi of native plant roots in a grassland site in California and one in Utah. In the California site, we used experimentally created plant communities composed of exotic (Avena barbata, Bromus hordeaceus) and native (Nassella pulchra, Lupinus bicolor) monocultures and mixtures. In the Utah semi-arid grassland, we took advantage of invasion by Bromus tectorum into long-term plots dominated by either of two native grasses, Hilaria jamesii or Stipa hymenoides. Arbuscular mycorrhizal fungi colonizing roots were characterized with PCR amplification of the ITS region, cloning, and sequencing. We saw a significant effect of the presence of exotic grasses on the diversity of mycorrhizal fungi colonizing native plant roots. In the three native grasses, richness of mycorrhizal fungi decreased; in the native forb at the California site, the number of fungal RFLP patterns increased in the presence of exotics. The exotic grasses also caused the composition of the mycorrhizal community in native roots to shift dramatically both in California, with turnover of Glomus spp., and Utah, with replacement of Glomus spp. by apparently non-mycorrhizal fungi. Invading plants may be able to influence the network of mycorrhizal fungi in soil that is available to natives through either earlier root activity or differential carbon provision compared to natives. Alteration of the soil microbial community by plant invasion can provide a mechanism for both successful invasion and the resulting effects of invaders on the ecosystem