Typha is an iconic wetland plant found worldwide. Hybridization and anthropogenic disturbances have resulted in large increases in Typha abundance in wetland ecosystems throughout North America at a cost to native floral and faunal biodiversity. As demonstrated by three regional case studies, Typha is capable of rapidly colonizing habitats and forming monodominant vegetation stands due to traits such as robust size, rapid growth rate, and rhizomatic expansion. Increased nutrient inputs into wetlands and altered hydrologic regimes are among the principal anthropogenic drivers of Typha invasion. Typha is associated with a wide range of negative ecological impacts to wetland and agricultural systems, but also is linked with a variety of ecosystem services such as bioremediation and provisioning of biomass, as well as an assortment of traditional cultural uses. Numerous physical, chemical, and hydrologic control methods are used to manage invasive Typha, but results are inconsistent and multiple methods and repeated treatments often are required. While this review focuses on invasive Typha in North America, the literature cited comes from research on Typha and other invasive species from around the world. As such, many of the underlying concepts in this review are relevant to invasive species in other wetland ecosystems worldwide.

The mechanisms by which invasive plants displace native species are often not well elucidated, limiting knowledge of invasion dynamics and the scientific basis for management responses. Typha 9 glauca Godr. invades wetlands throughout much of North America. Like other problematic wetland invaders, Typha is large, grows densely, and leaves behind copious litter. It thus has the potential to impact wetlands both in life and after death. We assessed patterns in field settings and used simulated wetland-plant communities to experimentally test abiotic and community responses to live Typha, Typha litter, and water-level differences (confounded in the field) using a full-factorial design. In general, litter was a stronger driver of change than live Typha. The greatest impacts were seen where, as in nature, live and dead Typha co-occurred. Live-Typha treatments did not differ from controls in light or temperature conditions but did reduce community biomass and alter community composition. Litter strongly affected light, temperature and its variability, community and species-level plant biomass, and community composition. Interactions between live Typha and litter affected aspects of plant-community composition. Advantageously for Typha, interspecific litter effects were not mirrored by intraspecific suppression of live Typha. These findings clarify how Typha is such an effective invader. Similar mechanisms are likely involved in invasions by other plant species, particularly in wetlands. Managers should respond quickly to new Typha invasions and, when dealing with established stands, remove litter in addition to eradicating live plants.

Climate change is predicted to reduce Laurentian Great Lakes water levels, altering coastal wetland ecosystems and potentially stimulating invasive macrophytes, like Typha X glauca. Recent prolonged low water levels, which climaxed in 2007, created conditions comparable to those predicted by climate change science. In 2008, we examined ecosystem and plant community properties in 14 intact northern Great Lakes coastal wetlands and compared community data with data from a 1987-1989 high-water period, before T. X glauca invasion. In 2008, T. X glauca occurred in 50% of wetlands and 16% of plots; was associated with reduced Floristic Quality and increased soil organic matter, soil nutrients, and leaf litter (all p<0.05); and plant community composition had shifted and was more homogeneous than in 1988 (both p<0.05). Additionally, T. X glauca was more dominant when growing behind barrier beach ridges, which form in high-water conditions and persist in low-water, than in lake-exposed marshes (p<0.05), revealing a physiographic mechanism for increased dominance. Beach ridges protect T. X glauca from wave and seiche energy, and as water levels decline, these energyinsulating microtopographic features will likely stimulate further invasion and dominance by T. X glauca, even in high quality wetlands.

Ecological and financial constraints limit restoration efforts, preventing the achievement of desired ecological outcomes. Harvesting invasive plant biomass for bioenergy has the potential to reduce feedback mechanisms that sustain invasion, while alleviating financial limitations. Typha × glauca is a highly productive invasive wetland plant that reduces plant diversity, alters ecological functioning, its impacts increase with time, and is a suitable feedstock for bioenergy. We sought to determine ecological effects of Typha utilization for bioenergy in a Great Lakes coastal wetland by testing plant community responses to harvest‐restoration treatments in stands of 2 age classes and assessing community resilience through a seed bank study. Belowground harvesting increased light penetration, diversity, and richness and decreased Typha dominance and biomass in both years post‐treatment. Aboveground harvesting increased light and reduced Typha biomass in post‐year 1 and in post‐year 2, increased diversity and richness and decreased Typha dominance. Seed bank analysis revealed that young stands (<20 years) had greater diversity, richness, seedling density, and floristic quality than old stands (>30 years). In the field, stand‐age did not affect diversity or Typha dominance, but old stands had greater Typha biomass and slightly higher richness following harvest. Harvesting Typha achieved at least 2 desirable ecological outcomes: reducing Typha dominance and increasing native plant diversity. Younger stands had greater potential for native recovery, indicated by more diverse seed banks. In similar degraded wetlands, a single harvest of Typha biomass would likely result in significant biodiversity and habitat improvements, with the potential to double plant species richness.

The ecological impacts of invasive plants increase dramatically with time since invasion. Targeting young populations for treatment is therefore an economically and ecologically effective management approach, especially when linked to post-treatment monitoring to evaluate the efficacy of management. However, collecting detailed field-based post-treatment data is prohibitively expensive, typically resulting in inadequate documentation of the ecological effects of invasive plant management. Alternative approaches, such as remote detection with unmanned aerial vehicles (UAV), provide an opportunity to advance the science and practice of restoration ecology. In this study, we sought to determine the plant community response to different mechanical removal treatments to a dominant invasive wetland macrophyte (Typha spp.) along an age-gradient within a Great Lakes coastal wetland. We assessed the post-treatment responses with both intensive field vegetation and UAV data. Prior to treatment, the oldest Typha stands had the lowest plant diversity, lowest native sedge (Carex spp.) cover, and the greatest Typha cover. Following treatment, plots that were mechanically harvested below the surface of the water differed from unharvested control and above-water harvested plots for several plant community measures, including lower Typha dominance, lower native plant cover, and greater floating and submerged aquatic species cover. Repeated-measures analysis revealed that above-water cutting increased plant diversity and aquatic species cover across all ages, and maintained native Carex spp. cover in the youngest portions of Typha stands. UAV data revealed significant post-treatment differences in normalized difference vegetation index (NDVI) scores, blue band reflectance, and vegetation height, and these remotely collected measures corresponded to field observations. Our findings suggest that both mechanically harvesting the above-water biomass of young Typha stands and harvesting older stands below-water will promote overall native community resilience, and increase the abundance of the floating and submerged aquatic plant guilds, which are the most vulnerable to invasions by large macrophytes. UAV's provided fast and spatially expansive data compared to field monitoring, and effectively measured plant community structural responses to different treatments. Study results suggest pairing UAV flights with targeted field data collection to maximize the quality of post-restoration vegetation monitoring.

The aggressive cattail species Typha X glauca and Typha angustifolia have established in wetlands across the Great Lakes region, decreasing native plant diversity and altering environmental conditions. We relied on a parallel study in which 80 years of historical aerial photographs from a large Lake Michigan wetland complex were used to map the spread and determine the age of invasive cattail stands. Floristic, edaphic, and environmental data were collected from plots across an invasion-age gradient. Compared with reference uninvaded sites, litter mass more than doubled within 10 years of invasion (P< 0.001), plant diversity declined by more than 50% within 25 years of invasion (P=0.003), and soil organic depth was more than 29-cm deeper in areas invaded for more than 35 years compared with areas invaded for 10 years or less (P=0.006). These time-dependent changes in plant communities, soil, and environmental conditions fundamentally alter the structure of invaded wetlands, likely influencing a range of ecosystem services.

In Laurentian Great Lakes coastal wetlands (GLCWs), dominant emergent invasive plants are expanding their ranges and compromising the unique habitat and ecosystem service values that these ecosystems provide. Herbiciding and burning to control invasive plants have not been effective in part because neither strategy addresses the most common root cause of invasion, nutrient enrichment. Mechanical harvesting is an alternative approach that removes tissue‐bound phosphorus and nitrogen and can increase wetland plant diversity and aquatic connectivity between wetland and lacustrine systems. In this study, we used data from three years of Great Lakes‐wide wetland plant surveys, published literature, and bioenergy analyses to quantify the overall areal extent of GLCWs, the extent and biomass of the three most dominant invasive plants, the pools of nitrogen and phosphorus contained within their biomass, and the potential for harvesting this biomass to remediate nutrient runoff and produce renewable energy. Of the approximately 212,000 ha of GLCWs, three invasive plants (invasive cattail, common reed, and reed canary grass) dominated 76,825 ha (36%). The coastal wetlands of Lake Ontario exhibited the highest proportion of invasive dominance (57%) of any of the Great Lakes, primarily from cattail. A single growing season's biomass of these invasive plants across all GLCWs was estimated at 659,545 metric tons: 163,228 metric tons of reed canary grass, 270,474 metric tons of common reed, and 225,843 metric tons of invasive cattail, and estimated to contain 10,805 and 1144 metric tons of nitrogen and phosphorus, respectively. A one‐time harvest and utilization for energy of this biomass would provide the gross equivalent of 1.8 million barrels of oil if combusted, or 0.9 million barrels of oil if converted to biogas in an anaerobic digester. We discuss the potential for mitigating non‐point source nutrient pollution with invasive wetland plant removal, and other potential uses for the harvested biomass, including compost and direct application to agricultural soils. Finally, we describe the research and adaptive management program we have built around this concept, and point to current limitations to the implementation of large‐scale invasive plant harvesting.

Invasive wetland plants are the primary targets of wetland management to promote native communities and wildlife habitat, but little is known about how commonly implemented restoration techniques influence nutrient cycling. We tested how experimental mowing, herbicide application, and biomass harvest (i.e., removal of aboveground biomass) treatments of Typha-invaded mesocosms altered porewater nutrient (NO 3 -, NH 4 ? , PO 4 -3 ) concentration and supply rate, vegetation response, and light penetration to the soil surface. We found that while herbicide application eliminated the target species, it also reduced native plant density and biomass, as well as increased porewater nutrient concentration (PO 4 -3 , NO 3 -) and supply rates (N, P, K) up to a year after treatments were implemented. Because herbicide application promotes nutrient enrichment, it may increase the likelihood of reinvasion by problematic wetland invaders, as well as cause eutrophication and deleterious algal blooms in adjacent aquatic systems. Our data suggest that biomass harvest should be considered by managers aiming to reduce Typha abundance without eradicating native diversity, avoid nutrient leaching, as well as possibly utilizing biomass for bioenergy.