The elusive invasive plant known as the Common Reed

 

Hailey Erb-Environmental Science

Renee DeAngelis- Turfgrass Management

Nick Falcione-Urban Forestry

George Burgress- Building Construction Technology

NAT SCI 387 Junior Year Writing

University of Massachusetts Amherst

 

In the North Shore of Massachusetts, local middle and high school students attend field trips to the famed “Great Marsh” that happens to reside in their own backyards. They are accompanied by Mass Audubon staff scientists who are on a mission to educate the local youth on the importance of a healthy wetland ecosystem by maintaining biodiversity. The Great Marsh in the North Shore of Massachusetts has the largest amount of coastal salt marsh in New England, and in 2004 it came to the attention of residents and stakeholders that the invasive plant common reed (Phragmites australis) has been affecting a substantial amount of native plants that established the biodiversity needed to maintain a healthy wetland ecosystem. Massive stands of common reed had displaced the once thriving wetland ecosystem. Natural salt marshes act as sanctuaries for unique aquatic plants, coastal birds, and extensive marine life. As brackish waters creep up from the sea and across the shores of a marsh, the diverse forms of life contained within are nourished with a medley of fresh and salt water. When the integrity of a wetland ecosystem is maintained, the wetland can provide services like clean water, flood control, fish and wildlife habitat, and groundwater supply. When threatened, the pristine beauty of salt marshes is not the only commodity at risk: humans may also suffer (Ringelheim, Filosa, Baumann, & Astle, 2005).

Invasion by common reed poses a significant threat to communities that rely on the services provided by salt marshes. Of particular interest is the impact of common reed on the fishing industry. The root of its impact lies in the ability of common reed to reduce the number and variety of plants living in wetlands (Ailstock, Norman, & Bushmann, 2001). Native plants that typically grow and thrive in tidal wetlands are essential to the fishing industry as they act as sources of oxygen, shelter, and food for estuary fish (Able, 1999). Smaller fish use estuary habitats as protection from game fish until the tide comes in, at which point larger game fish are able to enter salt marshes and eat the smaller estuary bait fish. Natural salt marsh communities are important parts of the ocean’s food chain, providing food for the larger fish that are vital to the New England fishing industry (Drociak, 2003). By crowding out native plants and reducing the provision of services that enable estuary fish to survive, common reed poses a threat to the fishing industry as a whole. The mechanisms by which common reed affects coastal communities are discussed at length below.

The effects of the invasive common reed on surrounding native plants can result in crowding out wetland environments that contain an abundance of biodiversity. Therefore, it is necessary to understand how rapidly this species can spread within wetland ecosystems when discussing solutions to reduce or eradicate invasive plants. Common reed can rapidly spread through the air, producing more than 2,000 seeds each year. Common reed can also invade underground through massive root systems that spread over ten feet from a single plant. This mechanism of reproduction gives the common reed a distinct advantage over other native plants. For instance, Pickleweed (Salicornia virginica), is a common marshland plant that is grows low to the ground in ranges between 30-90 cm in height (Pacific, 2019). Due to Pickleweed growing extremely low to the ground, it makes the plant vulnerable to becoming overcrowded by the common reed due to the combination of both a high reproduction rate and its towering height of up to 3 meters. Common reed can tolerate highly adverse conditions which are not favorable to most other native plants giving it a distinct advantage when invading foreign areas. Poor soil quality and rapid changes in soil biochemistry pose little problem to the highly resilient invasive species, though other plant species may struggle to survive in such conditions. Additionally, the common reed can degrade the health of surrounding plant communities by rapid assimilation, or uptake, of minerals which deplete the surrounding soil of nutrients. Only minimal amounts of these nutrients return to the soil upon death due to the common reed’s limited decomposition capacity (Kim et al., 2018). Plants growing near the shoots of the common reed are often unable to obtain levels of nutrients and water particles necessary for healthy development and survival. Thus, wetland ecosystems with low nutrient content and reduced salinity are easy targets for common reed (Silliman & Bertness, 2004).

Invasion by common reed poses a significant threat to U.S. fishing industries. When talking about common reed and the effects it has on fish density rates it is important to understand how the invasive species impacts the waters it inhabits. Many of the plant species native to wetlands and salt marshes provide the waters they inhabit with oxygen, these plants are the waters cleansers (Amsberry et al., 2000). Common reed crowds out these plant species when it invades salt marshes leaving the water less oxygen, in turn, it impacts the U.S fishing industry by reducing water quality. All fish need oxygen to survive, especially estuary bait fish. For these fish to survive waters need to have at least 4.8 mg O2/L (Able, 1999). Estuary fish are food for game fish such as striped bass, fluke, haddock and many others that are the backbone of the seafood market and the fishing industry as a whole. The fishing industry is extremely important to U.S. and international economies, particularly in coastal areas. In coastal communities, the fishing industry provides employment for 1.7 million jobs in the U.S as of 2012 (Kearney, 2014). While many community members are actual fishermen, many others are employed in industries that rely entirely on fishing, from fish processing warehouses to seafood retailers and restaurants. Coastal communities members rely heavily on the commercial and recreational fishing operations that sustain their livelihoods and contribute billions of dollars each year to the U.S. economy. The economic contribution of fishing in the United States is incredibly large: the U.S. fishing industry produces over $90 billion in revenue each year (Radtke, Dewees, & Smith, 1987). Anyone who enjoys seafood, recreation fishing, or cares about the environment should have a vested interest in this issue, which is a serious threat to U.S. ecosystems and the many communities dependent on them (Harris, Hershbein, & Kearney, 2014). The diverse and devastating effects of the common reed on U.S. ecosystems and economies provide more than enough of a reason to control the plant’s rapidly expanding populations.

Proposal:

Though there are a variety of techniques used to manage common reed populations, few are fully effective at eliminating the plant when used alone, and reinvasion is quite likely when the management strategy is not maintained (Sturtevant, Fusar, Conard, & Iott, 2016). Popular management techniques include the use of herbicides, mowing, cutting, flooding, draining, burning, covering, and grazing (Blossey et al., 2013). However, these techniques are often labor intensive, expensive, and require multiple applications. Manual techniques like cutting and pulling, for example, are only effective in small stands of common reed and must be repeated annually for several years to keep the invasive plant from spreading (New York State Department of Environmental Conservation [NYSDEC], n.d.). Physical management strategies are often used in conjunction with chemical application to decrease the likelihood of common reed growing back (Sturtevant, Fusar, Conard, & Iott, 2016). The most popular and generally successful chemical control method is the application of glyphosate. However, herbicide application is generally a two year process (touch-ups are usually necessary) and requires pairing with physical management techniques like cutting or burning to be successful (NYSDEC, n.d.). Retreatment with glyphosate is needed every 3-5 years to maintain low numbers of common reed (Blossey et al., 2013). Glyphosate must also be very carefully applied as it is a non-selective herbicide, meaning it can kill most types of plants (NYSDEC, n.d.). Prior to 2010, the annual expenditures for herbicide use to treat common reed in the U.S. reached $4-5 million (Casagrande, H?fliger, Hinz, Tewksbury, & Blossey, 2018). Evidently, current control methods are quite costly and ineffective, particularly for large common reed populations (Blossey, 2007). The lack of options for easy, inexpensive, long-term control of common reed populations has led to a robust effort to find novel management strategies. Though there are no means of biological control currently approved for common reed in the United States (Sturtevant, Fusar, Conard, & Iott, 2016), insect-based biocontrol has tremendous potential for managing large populations of common reed over long periods of time. According to the United States Department of Agriculture [USDA] (2018), biocontrol is easy to use, safe to use, cost effective, environmentally sound, self-sustaining, and target specific – unlike traditional management strategies (para. 2).

To mitigate the devastating effects of common reed on U.S. ecosystems, federally-funded introduction of insects that feed on the plant should occur in areas infested or at-risk of infestation by common reed. The release of insects that feed on either the roots, shoots, stems or leaves of the plant are examples of biological control: the intentional introduction of a natural enemy to control a pest population. The insects chosen to act as biocontrol must be monophagous, meaning they exclusively consume members of a single species (eliminating the risk to other plant species). They must also feed on the shoots of the invasive plants. Shoot feeding insects are ideal to manage common reed because eliminating the shoots will decrease the likelihood that the invasive species will re-establish its populations. Success will stem from the evaluation of monophagous insects which can effectively and inexpensively destroy stands of common reed with a low risk of population re-establishment. Effective management treatments must be designed to reduce the impact of common reed on coastal communities and on the environment.

Many beneficial insects are commercially available, and can quickly reduce pest populations to manageable levels. Studies show that there are 26 insect species in North America and another 140 insect species in Europe that consume or attack common reed (Blossey et al., 2013; Tewksbury, Casagrande, Blossey, H?fliger, & Schwarlzl?nder, 2002). About half of these species are common reed specialists, meaning they actively pursue Phragmites plants (Blossey, Schwarzländer, Häfliger, Casagrande, & Tewksbury, 2002). Of the species mentioned above, Archanara geminipuncta (the shoot-boring moth known colloquially as the twin-spotted wainscot) is one of the best potential biological control agents for common reed (Blossey et al., 2013). When in its larval stage, the twin-spotted wainscot bores inside the shoots and feeds on the plant material inside. Research has shown that only after 14 days from when this species is introduced to populations of common reeds, 46% of shoots had larval feeding activity (Blossey et al., 2013). Potential introduction of exotic insect species from Europe that specifically target the shoots of the common reed can prove efficient for controlling the invasion and outbreak of common reed (Tewksbury et al., 2002). Of all potential biocontrol agents, the twin-spotted wainscot is also one of the easiest and least expensive to rear. Research on the potential of the twin-spotted wainscot to act as biocontrol for common reed is conducted across the globe – from the University of Rhode Island to Cornell University to the CABI Bioscience Center in Switzerland (Blossey et al., 2013).

The use of biocontrol for common reed is actually quite feasible, and can be funded in United States by federal or state governments. Common reed is recognized by the New York State Governor’s Invasive Species Task Force as the “number one invasive threat to marine environments” (Blossey, 2007, para. 1). The recognition of the threat posed by common reed to ecosystems and economies alike is reflected in the actions taken by the state of New York to control its spread. A 2004 survey of the Regions by the Environmental Analysis Bureau estimated that over $110,000 was spent each year on common reed control in New York State alone. In response, the state of New York wisely invested $500,000 in a two year biocontrol project conducted by a research group out of Cornell (Blossey, 2007). State organizations are clearly aware of the impacts of common reed invasion and willing to make investments to eradicate the problem – and New York is not alone. The United States Department of Agriculture operates a biological control program designed to defend natural areas from economic and ecological damages caused by invasive species (United States Department of Agriculture [USDA], 2018). Funded activities include research on potential biological control agents, research on techniques for the successful establishment, release and distribution of biocontrol agents, and continued monitoring of their impacts on pest species (USDA, 2018). Success stories are also common: large populations of the invasive plant purple loosestrife (Lythrum salicaria), for example, were successfully managed in several states using biological control (Blossey, 2007). The implementation of insect-based biocontrol for common reed is very feasible with support from government funding.

There is some concern regarding the potential of insects introduced to control invasive common reed to negatively affect native reed populations. This concern is largely responsible for the lack of availability of biocontrol options for the common reed in the United States (Sturtevant, Fusar, Conard, & Iott, 2016). While European strains of the common reed are invasive and cause widespread damage to U.S. ecosystems and economies, native populations have declined and are of significant conservation concern (Casagrande, H?fliger, Hinz, Tewksbury, & Blossey, 2018). Invasive common reed and native reeds are genetically distinct groups (though they are within the same species), meaning any biological control agent chosen to manage the invasive population must have incredibly high specificity (to the cultivar level). Otherwise, native reed populations could be put at risk by the introduced insect (Cronin, Kiviat, Meyerson, Bhattarai, & Allen, 2016). Opponents to biological control of common reed argue that this type of specificity is unprecedented. Biocontrol researchers, however, argue that herbivore specificity often occurs below the species level, and genotype specificity (in which insects/herbivores exclusively consume plants with a specific genetic composition) is a widespread phenomenon. For example, Boneset and bitou bush are related sub-species with effective sub-species specific biocontrol agents in Australia and New Zealand (Casagrande, H?fliger, Hinz, Tewksbury, & Blossey, 2018). These researchers also argue that the existence of closely related native species should not inhibit investigation, and that it is possible to reliably evaluate the risks to native subspecies through rigorous testing. The authors argue that their research indicates that the twin-spotted wainscot is one of the best potential candidates for biological control of exotic common reed, poses little risk to native common reed populations because native common reed has certain physical features that deter twin-spotted wainscots from consuming the plant. For example, female twin-spotted wainscots avoid laying eggs on the leaf-sheaths of native common reeds, which fall off during fall and winter – inhibiting survival rates. They are far more likely to lay their eggs on invasive common reed (which retains its leaf-sheaths), restricting attack to invasive common reed (Casagrande, H?fliger, Hinz, Tewksbury, & Blossey, 2018).

Common reeds’ rapid ability to spread and take over fragile salt marsh ecosystems makes it an invasive species. These salt marshes are home to many important native plant species, these native plants provide the water with oxygen sources and natural cleansers. Common reed crowds out these native plants negatively affecting biodiversity, and in turn, water quality. These salt marshes provide habits for many estuary bait fish. When common reed invades and crowds out native plant species, oxygen levels in the water drop. Oxygen levels are extremely important to estuary bait fish as they need it to breathe and survive. Bait fish are the fuel for the fishing industry, the loss of these salt marsh habitats is negatively affecting fish density populations. The fishing industry is a 90 billion dollar a year industry that provides many coastal economies with much of their economic support. The loss of salt marsh habitat is causing a chain reaction that ends up negatively affecting coastal communities. Many of these communities cannot survive with the current state of the fishing industry, people are forced to pack up their belongings and leave home. Controlling and mitigating common reed invasion is imperative to save these coastal communities and our salt marshes. By using biocontrols, such as monophagous insects to control common reed instead of herbicides, we avoid the many negative impacts on the environment and water these chemicals can cause.

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