Here\u27s the Dirt: The Newest Recommendations for Garlic Mustard Management

Garlic mustard (Alliaria petiolata) is an invasive plant that has quickly become naturalized throughout most of the United States. Due in part to high reproductive output and the release of chemical compounds that disturb beneficial plant-fungal associations, this species is able to outcompete many native plants. Over the years, different garlic mustard management strategies been prescribed and implemented with varying success. Here we summarize methods for the removal of garlic mustard based on the most recent literature and research conducted in our lab. We aim to provide a series of clear tasks that landowners, stakeholders, and managers may find useful regarding the eradication of garlic mustard

Projected Carbon Dioxide to Increase Grass Pollen and Allergen Exposure Despite Higher Ozone Levels

One expected effect of climate change on human health is increasing allergic and asthmatic symptoms through changes in pollen biology. Allergic diseases have a large impact on human health globally, with 10–30% of the population affected by allergic rhinitis and more than 300 million affected by asthma. Pollen from grass species, which are highly allergenic and occur worldwide, elicits allergic responses in 20% of the general population and 40% of atopic individuals. Here we examine the effects of elevated levels of two greenhouse gases, carbon dioxide (CO2), a growth and reproductive stimulator of plants, and ozone (O3), a repressor, on pollen and allergen production in Timothy grass (Phleum pratense L.). We conducted a fully factorial experiment in which plants were grown at ambient and/or elevated levels of O3 and CO2, to simulate present and projected levels of both gases and their potential interactive effects. We captured and counted pollen from flowers in each treatment and assayed for concentrations of the allergen protein, Phl p 5. We found that elevated levels of CO2 increased the amount of grass pollen produced by ∼50% per flower, regardless of O3 levels. Elevated O3 significantly reduced the Phl p 5 content of the pollen but the net effect of rising pollen numbers with elevated CO2 indicate increased allergen exposure under elevated levels of both greenhouse gases. Using quantitative estimates of increased pollen production and number of flowering plants per treatment, we estimated that airborne grass pollen concentrations will increase in the future up to ∼200%. Due to the widespread existence of grasses and the particular importance of P. pratense in eliciting allergic responses, our findings provide evidence for significant impacts on human health worldwide as a result of future climate change

Responses of non-native earthworms to experimental eradication of garlic mustard and implications for native vegetation

Recent studies in invasion biology suggest that positive feedback among two or more introduced organisms facilitate establishment within a new range and drive changes in native plant communities. Here, we experimentally tested for relationships between native plants and two non‐native organisms invading forest habitats in North America: garlic mustard (Alliaria petiolata, Brassicaceae) and earthworms. In two forested sites, we compared understory vegetation and earthworm biomass in plots where garlic mustard was removed for three years, plots without garlic mustard invasion, and plots invaded by garlic mustard that was not removed. Earthworm biomass was highest in the plots with garlic mustard, and long‐term eradication of garlic mustard reduced earthworm biomass to levels similar to those observed in the uninvaded control plots. Invasion treatment, and the interactions between earthworm biomass and treatment, explained most of the variation in plant community composition and diversity—suggesting that earthworms alone do not necessarily drive forest understory floristic patterns. In contrast to broader geographic patterns indicating earthworms as the main driver of vegetation change in the presence of non‐native plants, we show that garlic mustard solely, or in conjunction with earthworm biomass, drives changes in native plant composition and diversity at the scale of individual forests. From a local management perspective, our data suggest that garlic mustard eradication can directly assist in the conservation of native plant communities and simultaneously reduce earthworm biomass

Invasive species risk assessments need more consistent spatial abundance data

Spatial abundance information is a critical component of invasive plant risk assessment. While spatial occurrence data provide important information about potential establishment, abundance data are necessary to understand invasive species’ populations, which ultimately drive environmental and economic impacts. In recent years, the collective efforts of numerous management agencies and public participants have created unprecedented spatial archives of invasive plant occurrence, but consistent information about abundance remains rare. Here, we develop guidelines for the collection and reporting of abundance information that can add value to existing data collection efforts and inform spatial ecology research. In order to identify the most common methods used to report abundance, we analyzed over 1.6 million invasive plant records in the Early Detection and Distribution Mapping System (EDDMapS). Abundance data in some form are widely reported, with 58.9% of records containing qualitative or quantitative information about invasive plant cover, density, or infested area, but records vary markedly in terms of standards for reporting. Percent cover was the most commonly reported metric of abundance, typically collected in bins of trace (25%). However, percent cover data were rarely reported along with an estimate of area, which is critical for ensuring accurate interpretation of reported abundance data. Infested area is typically reported as a number with associated units of square feet or acres. Together, an estimate of both cover and infested area provides the most robust and interpretable information for spatial research and risk assessment applications. By developing consistent metrics of reporting for abundance, collectors can provide much needed information to support spatial models of invasion risk

Invasive Plant Suppresses the Growth of Native Tree Seedlings by Disrupting Belowground Mutualisms

The impact of exotic species on native organisms is widely acknowledged, but poorly understood. Very few studies have empirically investigated how invading plants may alter delicate ecological interactions among resident species in the invaded range. We present novel evidence that antifungal phytochemistry of the invasive plant, Alliaria petiolata, a European invader of North American forests, suppresses native plant growth by disrupting mutualistic associations between native canopy tree seedlings and belowground arbuscular mycorrhizal fungi. Our results elucidate an indirect mechanism by which invasive plants can impact native flora, and may help explain how this plant successfully invades relatively undisturbed forest habitat

New science, synthesis, scholarship, and strategic vision for society

Harvard Forest LTER (HFR) is a two decade-strong, integrated research and educational program investigating responses of forest dynamics to natural and human disturbances and environmental changes over broad spatial and temporal scales. HFR engages \u3e30 researchers, \u3e200 graduate and undergraduate students, and dozens of institutions in research into fundamental and applied ecological questions of national and international relevance. Through LTER I–IV, HFR has added historical perspectives, expanded its scope to the New England region, integrated social, biological, and physical sciences, and developed education and outreach programs for K-12, undergraduate, and graduate students, along with managers, decision-makers, and media professionals

Climate change impacts on the distribution of the allergenic plant, common ragweed (Ambrosia artemisiifolia) in the eastern United States.

Climate change is affecting the growth, phenology, and distribution of species across northeastern United States. In response to these changes, some species have been adversely impacted while others have benefited. One species that has benefited from climate change, historically and in response to experimental treatments, is common ragweed (Ambrosia artemisiifolia), a widely distributed annual weed and a leading cause of hay fever in North America. To better understand how climate change may affect the distribution of common ragweed, we built a maximum entropy (Maxent) predictive model using climate and bioclimatic data and over 700 observations across the eastern U.S. Our model performed well with an AUC score of 0.765 using four uncorrelated variables, including precipitation seasonality, mean diurnal temperature range, August precipitation, and January maximum temperature. After building and testing our model, we then projected potential future common ragweed distribution using a suite of 13 global climate models (GCMs) under two future greenhouse gas scenarios for mid and late-century. In addition to providing georeferenced hot spots of potential future expansion, we also provide a metric of confidence by evaluating the number of GCMs that agree. We show a substantial contraction of common ragweed in central Florida, southern Appalachian Mountains, and northeastern Virginia and areas of potential expansion at the northern margins of its current distribution, notably in northeastern U.S. However, the vast majority of this increase is projected to occur by mid-century and may be moderated somewhat by the 2070s, implying that common ragweed may be sensitive to climatic variability. Although other factors and modeling approaches should be explored, we offer preliminary insight into where common ragweed might be a new concern in the future. Due to the health impacts of ragweed, local weed control boards may be well advised to monitor areas of expansion and potentially increase eradication efforts

Catching up on global change: new ragweed genotypes emerge in elevated CO2 conditions

Resource uptake by neighboring plants can be an important driver of natural selection in a changing environment. As climate and resource conditions are altered, genotypes that dominate within mixed populations today may differ markedly from those in future landscapes. We tested whether and how the dominance of different genotypes of the allergenic plant, common ragweed, may change in response to projected atmospheric CO2 conditions. We grew twelve maternal lines in experimental stands at either ambient or twice‐ambient levels of CO2. We then constructed a model that combines classical quantitative genetics theory with a set of a priori predictions about the relative performance of genotypes in the two treatments. Our findings show a complete reversal in the genotypic size hierarchy of ragweed plants in response to projected atmospheric CO2 conditions. Genotypes that are competitively suppressed in size at ambient levels become dominant under experimental doubling of CO2. Subordinated plants, in turn, boost their reproductive allocation to that of dominants, shrinking the fitness gap among all genotypes in high CO2. Extending our model to a contextual analysis framework, we further show that natural selection on size is reduced at elevated CO2, because an individual's position within the size hierarchy becomes less important for reproduction than it is in ambient conditions. Our work points to potential future ecological and evolutionary changes in this widespread allergenic plant

Tree seedling responses to multiple environmental stresses: Interactive effects of soil warming, nitrogen fertilization, and plant invasion

Temperate deciduous forest ecosystems in northeastern North America are under increasing biotic and abiotic stresses that can have interactive effects on understory vegetation, and thus impact the next generation of forest canopy trees. We examined seedling responses of the common and increasingly dominant species Acer rubrum (red maple) to the combined effects of soil warming (+5 °C), chronic nitrogen fertilization (+50 kg N ha−1 yr−1), and invasion by the phytotoxic plant Alliaria petiolata (garlic mustard), and their interactions. We planted 296 first-year A. rubrum seedlings in a multifactorial field experiment to examine the effects of all combinations of the experimental treatments. Second-year Acer rubrum seedlings demonstrated higher aboveground growth under soil warming conditions. Further, soil warming positively influenced plant-soil feedbacks through higher arbuscular mycorrhizal colonization in fine roots. However, the positive growth responses and mycorrhizal colonization observed under soil warming were moderated by both N fertilization and A. petiolata invasion. Our results highlight the importance of developing management plans that consider how multiple environmental change factors affect tree seedling performance, particularly via the plant-soil interface

Red hot maples: Acer rubrum first-year phenology and growth responses to soil warming

Microhabitat environmental conditions are an important filter for seedling establishment, controlling the availability of optimal recruitment sites. Understanding how tree seedlings respond to warming soil temperature is critical for predicting population recruitment in the future hardwood forests of northeastern North America, particularly as environmental conditions and thus optimal microhabitat availabilities change. We examined the effect of 5Ë C soil warming during the first growing season on germination, survival, phenology, growth, stem and root biomass allocation in Acer rubrum (red maple) seedlings. While there was no effect of soil warming on germination or survival, seedlings growing in warmer soils demonstrated significantly accelerated leaf expansion, delayed autumn leaf senescence, and an extended leaf production period. Further, seedlings growing in warmer soils showed larger leaf area, stem and root structures at the end of the first growing season, with no evidence of biomass allocation tradeoffs. Results suggest A. rubrum seedlings can capitalize on soil warming by adjusting leaf phenology and leaf production, resulting in a longer period of carbon uptake and leading to higher overall biomass. The absence of growth allocation tradeoffs suggests A. rubrum will respond positively to increasing soil temperatures in northeastern forests, at least in the early life stages.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author