Non-native Phragmites can negatively affect the biodiversity and ecological functions of invaded habitats, impair the recreational use of wetlands and shorelines, decrease property values, and increase fire risk. This section covers a variety of concerns brought on by the spread of Phragmites throughout the Great Lakes region.
Native Phragmites has been present in North-America for over 3,000 years. However, the non-native Phragmites is now more widespread, particularly in disturbed environment such as roadsides and drainage ditches (visit the Native vs. invasive? and Where is it found?). The spread of non-native Phragmites into natural wetlands of the Great Lakes basin could have detrimental impacts on the native strain. This further increases the complexity of Phragmites management programs, as managers need to develop control strategies that will successfully reduce non-native Phragmites populations without affecting the native strain.
It was long thought that the two strains of Phragmites could not hybridize as they bloom and senesce at different times. However, researchers from the University of Rhode Island were able to produce viable hybrid seedlings by cross-pollinating non-native and native Phragmites. Hybrids were recently discovered in two populations of Lake Erie, but hybridization is still believed to be rather uncommon. Potential large-scale hybridization of the two subspecies nevertheless remains a great concern, as this could lead to a genetic pollution of the native strain, or the creation of an aggressive hybrid.
- Meyerson. 2007. Native versus introduced Phragmites australis– What are the differences and why should we care? Bulletin of the Rhode Island Wild Plant Society.
- Meyerson, Lambertini, McCormick and Whigham. 2012. Hybridization of common reed in North-America? The answer is blowing in the wind. AoB Plants.
- Paul, Vachon, Garroway and Freeland. 2010. Molecular data provide strong evidence of natural hybridization between native and introduced lineages of Phragmites australis in North America. Biological Invasions 12(9): 2967-2973 [visit the Biological Invasions Journal website to read the abstract and get a reprint].
Non-native Phragmites produce large quantities of seed and can expand rapidly via vegetative growth, which enables it to quickly colonize new habitats and dominate areas in which it is established (see the How does it spread? section for more details on its reproduction mechanisms). As with many other invasive species, Phragmites can flourish in a wide range of environmental conditions, such as pH, salinity, or soil type. Several studies have demonstrated that Phragmites tends to become the dominant species in a variety of moist habitats, and that increasing Phragmites generally leads to decreases in the overall biomass, richness and abundance of native plant species.
- Chambers, Meyerson and Saltonstall. 1999. Expansion of Phragmites australis into tidal wetlands of North-America. Aquatic Botany 64(3): 261-273 [visit the Aquatic Botany website to read the abstract and obtain a reprint].
- Holdredge and Bertness. 2011. Litter legacy increases the competitive advantage of invasive Phragmites in New England wetlands. Biological Invasions 13(2): 423-433 [visit the Biological Invasions website to read the abstract and request a reprint].
- Resources: Rudrappa et al. (2007) Root-secreted Allelochemical in the Noxious WeedPhragmites australis Deploys a Reactive Oxygen Species Response and Microtubule Assembly Disruption to Execute Rhizotoxicity. Journal of Chemical Ecology. Volume 33, Number 10 (2007), 1898-1918.
Impacts of non-native Phragmites on animals are less clear and tend to vary between taxa. Phragmites stems and leaves have poor nutritional value and very few organisms seem to be feeding on it in North America. Replacement of native vegetation by the less nutritious Phragmites could have negative consequences for herbivores. And, while Phragmites colonies may provide habitats for certain species, there are many other species that may be negatively impacted by loss of other habitat types.
Fish at their larval and juvenile stages seems to be the most affected by Phragmites. The species produces an abundant litter which can reduce the mobility of juvenile fish in creeks. Effect on mature fish varies among species. Spotkin killifish, mummichog and northern pike were all shown to be less abundant within Phragmites communities.
Currently very little is known about potential impacts of Phragmites on amphibians. Preliminary results of a research conducted in freshwater marshes of Quebec did show no significant impacts on northern leopard frogs, green frogs and spring peeper, while a field experiment conducted in Connecticut found that larval American bullfrogs were positively effected by non-native Phragmites.
- Rogalski and Skelly. 2012. Positive effects of Nonnative Phragmites australis on larval Bullfrogs. PLOS One 7(8).
- Warren, Fell, Grimsby, Buck, Rilling and Fertik. 2001. Rates, patterns, and impacts of Phragmites australis expansion and effects of experimental Phragmites control on vegetation, macroinvertebrates, and fish within tidelands of the lower Connecticut River. Esturaries 24(1): 90-107 [visit the Estuaries website to read the abstract and request a reprint].
Phragmites is an ecosystem engineer- a species that can successfully modify the form and function of the habitats in which it is found. For example, the rapid growth and slow decomposition of above-ground biomass leads to large accumulations of organic material over several growing seasons. This can lead to greater rates of sediments deposition which can increase the elevation of invaded marshes and affect drainage, leading invaded marshes to slowly become drier, in turn, causing further changes in the remnant plant population at a site.
Check out this great fact sheet by the Midwest Invasive Plant Network: Why Should I Care About Invasive Plants?