Studies on invasive plant management are often short in duration and limited in the methods tested, and lack an adequate description of plant communities that replace the invader following removal. Here we present a comprehensive review of management studies on a single species, in an effort to elucidate future directions for research in invasive plant management. We reviewed the literature on Phragmites management in North America in an effort to synthesize our understanding of management efforts, identify gaps in knowledge and improve the efficacy of management. Additionally, we assessed recent ecological findings concerning Phragmites mechanisms of invasion and integrated these findings into our recommendations for more effective management. Our overall goal is to examine whether or not current management approaches can be improved and whether they promote reestablishment of native plant communities. We found: (i) little information on community-level recovery of vegetation following removal of Phragmites; and (ii) most management approaches focus on the removal of Phragmites from individual stands or groups of stands over a relatively small area. With a few exceptions, recovery studies did not monitor vegetation for substantial durations, thus limiting adequate evaluation of the recovery trajectory. We also found that none of the recovery studies were conducted in a landscape context, even though it is now well documented that land-use patterns on adjacent habitats influence the structure and function of wetlands, including the expansion of Phragmites. We suggest that Phragmites management needs to shift to watershed-scale efforts in coastal regions, or larger management units inland. In addition, management efforts should focus on restoring native plant communities, rather than simply eradicating Phragmites stands. Wetlands and watersheds should be prioritized to identify ecosystems that would benefit most from Phragmites management and those where the negative impact of management would be minimal.

Phragmites australis is a cosmopolitan grass and often the dominant species in the ecosystems it inhabits. Due to high intraspecific diversity and phenotypic plasticity, P. australis has an extensive ecological amplitude and a great capacity to acclimate to adverse environmental conditions; it can therefore offer valuable insights into plant responses to global change. Here we review the ecology and ecophysiology of prominent P. australis lineages and their responses to multiple forms of global change. Key findings of our review are that: (1) P. australis lineages are well-adapted to regions of their phylogeographic origin and therefore respond differently to changes in climatic conditions such as temperature or atmospheric CO₂; (2) each lineage consists of populations that may occur in geographically different habitats and contain multiple genotypes; (3) the phenotypic plasticity of functional and fitness-related traits of a genotype determine the responses to global change factors; (4) genotypes with high plasticity to environmental drivers may acclimate or even vastly expand their ranges, genotypes of medium plasticity must acclimate or experience range-shifts, and those with low plasticity may face local extinction; (5) responses to ancillary types of global change, like shifting levels of soil salinity, flooding, and drought, are not consistent within lineages and depend on adaptation of individual genotypes. These patterns suggest that the diverse lineages of P. australis will undergo intense selective pressure in the face of global change such that the distributions and interactions of co-occurring lineages, as well as those of genotypes within-lineages, are very likely to be altered. We propose that the strong latitudinal clines within and between P. australis lineages can be a useful tool for predicting plant responses to climate change in general and present a conceptual framework for using P. australis lineages to predict plant responses to global change and its consequences.

Summary: 1. A fundamental challenge to invasion ecology is to determine what factors cause an exotic species to spread rapidly long after the initial introduction. The increase of a resource (e.g. nitrogen) could trigger an expansion, but in other instances, species have overcome biological limitations (e.g. an Allee effect) like accumulating sufficient genetic diversity for successful reproduction. Understanding the ecological mechanisms governing plant invasions, such as nutrient enrichment or Allee effects, can be used to improve invasive plant management.2. We used the invasive, introduced grass Phragmites australis as a model to evaluate the role of nutrient enrichment and Allee effects in invasion. Based on recent studies that demonstrated the importance of sexual reproduction in this plant’s spread, we chose to focus our efforts on reproductive output. We examined the effects of patch‐level genetic diversity on viable seed production across watersheds of the Chesapeake Bay, USA, with differing levels of anthropogenic development (a proxy for nutrient enrichment). In an outdoor mesocosm experiment, we treated Phragmites plants originating from forested and developed watersheds with elevated vs. ambient nutrients and cross vs. self‐pollination and determined the effects on viable seed, floret and inflorescence production.3. The proportion of viable seeds produced at field sites varied widely and was not directly related to watershed development. Instead, seed viability was positively related to patch‐level genetic diversity, and patches in more developed watersheds had higher genetic diversity. Also, plants in larger patches produced a higher proportion of viable seeds. In the mesocosm experiment, seed viability was substantially higher for out‐crossed plants. Elevated nutrients resulted in greater floret and inflorescence production, particularly for plants originating from developed vs. forested watersheds.4. These findings have important management implications: small populations should be controlled before they accumulate sufficient genetic variation for prolific viable seed production, and landscape‐scale nutrient management could further limit reproductive output.5. Synthesis and applications. Our research shows how nutrient enrichment and a weak Allee effect can interact across multiple scales to impact invasion success and how understanding the ecological mechanisms governing plant invasions can be used to better inform invasive plant management.

The number of patches of non-native Phragmites australis in brackish tidal wetlands in the Rhode River subestuary increased from 5 in 1971–72 to 212 in 2007, and the area covered by the patches increased more than 25 times during the same time interval. Genetic analysis of the patches showed that the expansion has primarily been from seed, and genetic similarities between patches indicate that most cross-pollination occurs within a distance of 50 m. Comparison of patches in different parts of the subestuary indicate that the expansion of Phragmites australis has occurred at the scale of the entire subestuary and not the scale of subsections of the subestuary dominated by differing upland land-uses.