Management of invasive Phragmites australis in the Adirondacks: a cautionary tale about prospects of eradication

Repeated large-scale mechanical treatment of invasive Typha under increasing water levels promotes floating mat formation and wetland methane emissions

Invasive species management typically aims to promote diversity and wildlife habitat, but little is known about how management techniques affect wetland carbon (C) dynamics. Since wetland C uptake is largely influenced by water levels and highly productive plants, the interplay of hydrologic extremes and invasive species is fundamental to understanding and managing these ecosystems. During a period of rapid water level rise in the Laurentian Great Lakes, we tested how mechanical treatment of invasive plant Typha × glauca shifts plant-mediated wetland C metrics. From 2015 to 2017, we implemented large-scale treatment plots (0.36-ha) of harvest (i.e., cut above water surface, removed biomass twice a season), crush (i.e., ran over biomass once mid-season with a tracked vehicle), and Typha-dominated controls. Treated Typha regrew with approximately half as much biomass as unmanipulated controls each year, and Typha production in control stands increased from 500 to 1500 g-dry mass m^-2 yr^-1 with rising water levels (~10 to 75 cm) across five years. Harvested stands had total in-situ methane (CH₄) flux rates twice as high as in controls, and this increase was likely via transport through cut stems because crushing did not change total CH₄ flux. In 2018, one year after final treatment implementation, crushed stands had greater surface water diffusive CH₄ flux rates than controls (measured using dissolved gas in water), likely due to anaerobic decomposition of flattened biomass. Legacy effects of treatments were evident in 2019; floating Typha mats were present only in harvested and crushed stands, with higher frequency in deeper water and a positive correlation with surface water diffusive CH₄ flux. Our study demonstrates that two mechanical treatments have differential effects on Typha structure and consequent wetland CH₄ emissions, suggesting that C-based responses and multi-year monitoring in variable water conditions are necessary to accurately assess how management impacts ecological function.

Glyphosate Toxicity to Native Nontarget Macrophytes Following Three Different Routes of Incidental Exposure

A major goal of invasive plant management is the restoration of native biodiversity, but effective methods for invasive plant control can be harmful to native plants. Informed application of control methods is required to reach restoration goals. The herbicide glyphosate, commonly applied in invasive plant management, can be toxic to native macrophytes. Our study assessed the response of 2 macrophytes that are endangered in our study area (Ammannia robusta and Sida hermaphrodita) to glyphosate concentrations that mimic incidental exposure from nearby invasive plant control: spray drift of 4 × 10-7 % to 5% glyphosate; pulse and continuous immersion in water containing 2 to 41 µg/L glyphosate; and rhizosphere contact with 5%-glyphosate-wicked invasive plants. We assessed macrophyte sensitivity at 14-d postexposure, and quantified abundance of arbuscular mycorrhizal fungi. Glyphosate spray concentrations as low as 0.1% reduced macrophyte growth. Ammannia was more sensitive overall to glyphosate spray than Sida, although sensitivity varied among measured endpoints. Conversely, macrophytes were not affected by immersion in low concentrations of glyphosate or rhizosphere contact with a glyphosate-wicked plant. Likewise, arbuscular mycorrhizal fungi abundance in roots was similar among glyphosate-sprayed and control plants. Based on our results, we recommend that invasive plant managers reduce risks to native nontarget plants through implementing measures that limit off-target spray drift, and consider the feasibility of more targeted applications, such as with wick equipment. Integr Environ Assess Manag 2021;17:597-613. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Effects of invasive wetland macrophytes on habitat selection and movement by freshwater turtles

Invasive species can significantly impact native wildlife by structurally altering habitats and access to resources. Understanding how native species respond to habitat modification by invasive species can inform effective habitat restoration, avoiding inadvertent harm to species at risk. The invasive graminoids Phragmites australis australis (hereafter Phragmites) and Typha ×  glauca are increasingly dominating Nearctic wetlands, often outcompeting native vegetation. Previous research suggests that turtles may avoid invasive Phragmites when moving through their home ranges, but the mechanisms driving avoidance are unclear. We tested two hypotheses that could explain avoidance of invaded habitat: (1) that stands of invasive macrophytes (Phragmites and Typha x glauca) impede movement, and (2) that they provide inadequate thermal conditions for turtles. We quantified active-season movements of E. blandingii (n = 14, 1328 relocations) and spotted turtles (Clemmys guttata; n = 12, 2295 relocations) in a coastal wetland in the Laurentian Great Lakes. Neither hypothesis was supported by the data. Phragmites and mixed-species Typha stands occurred within the home ranges of mature, active E. blandingii and C. guttata, and were used similarly to most other available habitats, regardless of macrophyte stem density. Turtles using stands of invasive macrophytes did not experience restricted movements or cooler shell temperatures compared to other wetland habitat types. Control of invasive macrophytes can restore habitat heterogeneity and benefit native wetland species. However, such restoration work should be informed by the presence of at-risk turtles, as heavy machinery used for control or removal may injure turtles that use these stands as habitat.

The social-ecological system driving effective invasive plant management: two case studies of non-native Phragmites

Globally, the management of invasive plants is motivated by a desire to improve ecosystem services (e.g., recreation, flood mitigation, soil fertility for agriculture, aesthetics) and critical habitat for imperiled species. To reduce invader populations and impacts, it is important to document the social and ecological basis (i.e., the social-ecological system) for the management that has been employed and areas where a greater level of coordination among stakeholder groups (managers, scientists, legislators, resource users) could improve efforts. We present a conceptual model that builds on current thinking for how best to connect these four stakeholder groups-to foster stronger citizen lobbying for impacted resources, science-based governance, legislator-driven noxious weed laws and funding for management and science, knowledge co-production by scientists and managers, and co-management by managers and resource users. In light of our model, we present two case studies based in Nebraska and Utah, U.S.A. involving a common North American wetland invader, Phragmites australis (non-native common reed). In Nebraska, potential lawsuits stemming from water conveyance was strong motivation for funding management. In Utah, duck hunters and other resource users initially instigated management. Progress toward the successful management of Phragmites has been the result of manager-scientist partnerships addressing a knowing-doing gap among practitioners, the complexities of management mosaics, as well as overcoming economic and logistical constraints. Our model demonstrates how legislative initiatives can fund new research and bolster on-going management, while organically building strong partnerships among scientists, managers, and resource users that are key for successfully managing invasive species.

Nitrogen immobilization may reduce invasibility of nutrient enriched plant community invaded by Phragmites australis

Nutrient enrichment, particularly nitrogen, is an important determinant of plant community productivity, diversity and invasibility in a wetland ecosystem. It may contribute to increasing colonization and dominance of invasive species, such as Phragmites australis, especially during wetland restoration. Providing native species a competitive advantage over invasive species, manipulating soil nutrients (nitrogen) may be an effective strategy to control the invasive species and that management tool is essential to restore the degraded ecosystems. Therefore, we examined competition between Phragmites australis and Melaleuca ericifolia in a greenhouse setting with activated carbon (AC) treatments, followed by cutting of Phragmites shoots in nutrient-rich soils. Additionally, we evaluated the effect of AC on plant-free microcosms in the laboratory, to differentiate direct effects of AC on soil microbial functions from indirect effects. Overall, the objective was to test whether lowering nitrogen might be an effective approach for reducing Phragmites invasion in the wetland. The AC reduced Phragmites total biomass more significantly in repeated cut regime (57%) of Phragmites shoots compared to uncut regime (39%). Conversely, it increased Melaleuca total biomass by 41% and 68% in uncut and repeated cut regimes, respectively. Additionally, AC decreased more total nitrogen in above-ground biomass (41 to 55%) and non-structural carbohydrate in rhizome (21 to 65%) of Phragmites, and less total nitrogen reduction in above-ground biomass (25 to 24%) of Melaleuca in repeated cut compared to uncut regime. The significant negative correlation between Phragmites and Melaleuca total biomass was observed, and noticed that Phragmites acquired less biomass comparatively than Melaleuca in AC-untreated versus AC-treated pots across the cutting frequency. AC also caused significant changes to microbial community functions across Phragmites populations, namely nitrogen mineralization, nitrification, nitrogen microbial biomass and dehydrogenase activity (P ≤ 0.05) that may potentially explain changes in plant growth competition between Phragmites and Melaleuca. The overall effects on plant growth, however, may be partially microbially mediated, which was demonstrated through soil microbial functions. Results support the idea that reducing community vulnerability to invasion through nutrient (nitrogen) manipulations by AC with reducing biomass of invasive species may provide an effective strategy for invasive species management and ecosystem restoration.

When misconceptions impede best practices: evidence supports biological control of invasive Phragmites

Development of a biological control program for invasive Phagmites australis australis in North America required 20 years of careful research, and consideration of management alternatives. A recent paper by Kiviat et al. (Biol Invasions 21:2529–2541, 2019. 10.1007/s10530-019-02014-9) articulates opposition to this biocontrol program and questions the ethics and thoroughness of the researchers. Here we address inaccuracies and misleading statements presented in Kiviat et al. (2019), followed by a brief overview of why biological control targeting Phragmites in North America can be implemented safely with little risk to native species. Similar to our colleagues, we are very concerned about the risks invasive Phragmites represent to North American habitats. But to protect those habitats and the species, including P. australis americanus, we come to a different decision regarding biological control. Current management techniques have not been able to reverse the invasiveness of P. australis australis, threats to native rare and endangered species continue, and large-scale herbicide campaigns are not only costly, but also represent threats to non-target species. We see implementation of biocontrol as the best hope for managing one of the most problematic invasive plants in North America. After extensive review, our petition to release two host specific stem miners was approved by The Technical Advisory Group for the Release of Biological Control Agents in the US and Canadian federal authorities.

Invasive Phragmites australis management outcomes and native plant recovery are context dependent

The outcomes of invasive plant removal efforts are influenced by management decisions, but are also contingent on the uncontrolled spatial and temporal context of management areas. Phragmites australis is an aggressive invader that is intensively managed in wetlands across North America. Treatment options have been understudied, and the ecological contingencies of management outcomes are poorly understood. We implemented a 5-year, multi-site experiment to evaluate six Phragmites management treatments that varied timing (summer or fall) and types of herbicide (glyphosate or imazapyr) along with mowing, plus a nonherbicide solarization treatment. We evaluated treatments for their influence on Phragmites and native plant cover and Phragmites inflorescence production. We assessed plant community trajectories and outcomes in the context of environmental factors. The summer mow, fall glyphosate spray treatment resulted in low Phragmites cover, high inflorescence reduction, and provided the best conditions for native plant recruitment. However, returning plant communities did not resemble reference sites, which were dominated by ecologically important perennial graminoids. Native plant recovery following initial Phragmites treatments was likely limited by the dense litter that resulted from mowing. After 5 years, Phragmites mortality and native plant recovery were highly variable across sites as driven by hydrology. Plots with higher soil moisture had greater reduction in Phragmites cover and more robust recruitment of natives compared with low moisture plots. This moisture effect may limit management options in semiarid regions vulnerable to water scarcity. We demonstrate the importance of replicating invasive species management experiments across sites so the contingencies of successes and failures can be better understood.

Abiotic and Landscape Factors Constrain Restoration Outcomes Across Spatial Scales of a Widespread Invasive Plant

The natural recolonization of native plant communities following invasive species management is notoriously challenging to predict, since outcomes can be contingent on a variety of factors including management decisions, abiotic factors, and landscape setting. The spatial scale at which the treatment is applied can also impact management outcomes, potentially influencing plant assembly processes and treatment success. Understanding the relative importance of each of these factors for plant community assembly can help managers prioritize patches where specific treatments are likely to be most successful. Here, using effects size analyses, we evaluate plant community responses following four invasive Phragmites australis management treatments (1: fall glyphosate herbicide spray, 2: summer glyphosate herbicide spray, 3: summer imazapyr herbicide spray, 4: untreated control) applied at two patch scales (12,000 m2 and 1,000 m2) and monitored for 5 years. Using variation partitioning, we then evaluated the independent and shared influence of patch scale, treatment type, abiotic factors, and landscape factors on plant community outcomes following herbicide treatments. We found that Phragmites reinvaded more quickly in large patches, particularly following summer herbicide treatments, while native plant cover and richness increased at a greater magnitude in small patches than large. Patch scale, in combination with abiotic and landscape factors, was the most important driver for most plant responses. Compared with the small plots, large patches commonly had deeper and more prolonged flooding, and were in areas with greater hydrologic disturbance in the landscape, factors associated with reduced native plant recruitment and greater Phragmites cover. Small patches were associated with less flooding and landscape disturbance, and more native plants in the surrounding landscape than large patches, factors which promoted higher native plant conservation values and greater native plant cover and richness. Herbicide type and timing accounted for very little of the variation in native plant recovery, emphasizing the greater importance of patch selection for better management outcomes. To maximize the success of treatment programs, practitioners should first manage Phragmites patches adjacent to native plant species and in areas with minimal hydrologic disturbance.

Phytoremediation potential and control of Phragmites australis as a green phytomass: an overview

Phragmites australis (common reed) is one of the most extensively distributed emergent plant species in the world. This plant has been used for phytoremediation of different types of wastewater, soil, and sediments since the 1970s. Published research confirms that P. australis is a great accumulator for different types of nutrients and heavy metals than other aquatic plants. Therefore, a comprehensive review is needed to have a better understanding of the suitability of this plant for removal of different types of nutrients and heavy metals. This review investigates the existing literature on the removal of nutrients and heavy metals from wastewater, soil, and sediment using P. australis. In addition, after phytoremediation, P. australis has the potential to be used for additional benefits such as the production of bioenergy and animal feedstock due to its specific characteristics. Determination of adaptive strategies is vital to reduce the invasive growth of P. australis in the environment and its economic effects. Future research is suggested to better understand the plant's physiology and biochemistry for increasing its pollutant removal efficiency.