By Reid Plumb and Jerry Warmbold, Wildlife Biologists with Voyageurs National Park
Figure 1. A stand entirely comprised of invasive hybrid cattail in Voyageurs National Park, MN, USA. Photo Credit: Bryce Olson, NPS
Cattails, or more specifically broadleaf cattails (Typha latifolia), are a wetland plant native to most of North America. These sturdy perennials can grow almost 10ft tall (~3m), and in their natural state they are a wonderful wetland plant benefiting fish, wildlife, and ultimately even humans.
I think most folks understand the natural benefits of cattail for fish and wildlife species. Fish and aquatic macroinvertebrates (e.g., dragonfly larvae) use cattail as escape and breeding cover. Cattails are a primary food source for mammals such as muskrats, and essential nesting/roosting cover for multiple species of birds. Cattails are also great at filtering water, stabilizing erodible soils, slowing water flows and reducing the severity of floods, and sequestering carbon from the atmosphere.
But what about human benefits? Did you know cattails are a culturally significant plant used by indigenous peoples as a food source and for weaving materials? Or that it was used during World War II to make life jackets? Or that at the heart of the stem is a soft, edible shoot that has a texture and taste of a cucumber? Cattails are even not that bad as a pickled garnish in a Bloody Mary! Cattails also have industrial applications. The stems and foliage can be harvested and pelletized as a biofuel or can be distilled down into ethyl alcohol for use in products like antifreeze. The versatility of human uses for the plant is surprisingly impressive, but as with most things in life, too much of one of thing can sometimes be bad.
ORIGINS OF THE PROBLEM
As with most of the non-native invasive wetland plant species that threaten our native wetland communities (e.g., purple loosestrife [Lythrum salicaria]), narrowleaf cattail (Typha augustifolia) was first reported on the East Coast in the early part of the nineteenth century. Most scientists believe that narrowleaf cattail originated in Europe, and that as the expansion of European settlers went west, so too did the accounts of narrowleaf cattail. As the native broadleaf and non-native narrowleaf cattail overlapped, the two species began to hybridize, creating a new cattail species commonly referred to as “hybrid cattail” (Typha x glauca). Hybridization between native and introduced species is typically one of the primary drivers behind the evolution of invasiveness. Basically, hybrids often express the beneficial attributes of both parental species giving them an edge over their parental counter parts, a phenomenon known as “hybrid vigor”.
For example, hybrid cattails have been shown to tolerate a greater range of water depths or salinity than their parent species, which in turn allows hybrid cattails to expand into areas neither of the parent species could.
WHY IS THIS A PROBLEM?
Unlike the native broadleaf cattail, which evolved to co-exist with other native plant species, the invasive hybrid is competitively superior and can transform wetlands from a diverse mix of emergent, submergent, and floating-leaf vegetation to expansive stands of hybrid cattail monocultures (Fig. 1). This transformation generally degrades fish and wildlife habitat, reduces biodiversity, and outcompetes culturally significant plant resources like wild rice.
Figure 2. Cattail root system illustrating its ability to reproduce though vegetative expansion. Photo credit: Missouri Department of Conservation
Cattail reproductive mechanisms are a main reason hybrid cattail is efficient at invading and dominating wetland plant communities. Cattails reproduce in two ways, from seed or from cloning through rhizomes. Cattails can produce over 200,000 fluffy seeds in the spike of the plant that very easily spread by wind. If you have ever played with the cattail seed heads in the fall, you know the explosion of fluff that happens when you knock them around. Walking through a marsh in the late fall could sometimes be labeled as a choking hazard from all of the fluffy seeds that you breath in! Even the park’s snow groomers and snowmobiles sometimes succumb to the plight caused by cattail fluff, as they get sucked in the radiator and cause overheating issues.
Cattails also reproduce vegetatively through their rhizomes. The plant uses the rhizome to store starches, proteins, and other nutrients but as the rhizome grows out, it can produce new shoots and root systems at each node (Fig. 2). These new shoots are clones of the original plant. Over time, a complex spiderweb of rhizomes can spread through the wetland facilitating the vast cattail-dominated wetlands that are so common now. Examples of other common plants that have rhizomes are ginger, asparagus, and our favorite hops.
As if it could not get any worse, the hybrid cattail species has also learned how to float! Ok, well maybe not “learned” per se, but because it can tolerate a greater range of water depths, the further into deeper water it grows the more the natural buoyancy of the plant pulls at its roots, where it eventually lifts the root systems up off the bottom and becomes free-floating (Fig. 3). This process is reminiscent of walking out into a lake for a swim.
Figure 3. Illustration of how hybrid cattails grow out from shore and become a floating mat. Photo Credit: Bryce Olson, NPS
The further you walk out, the more buoyant you become. Eventually the water becomes too deep for you to touch, at which point you are floating or swimming at the surface. It really is the same principle.
You may ask “ok, but how does it do that?” The answer is pretty interesting. All cattails, like other emergent wetland plants, have submerged roots systems that have to “breathe” to survive in environments relatively devoid of atmospheric oxygen (i.e., wetland soils). The reason emergent plants can “breathe” is because of specialized tissues called aerenchyma tissue. This porous tissue acts as a snorkel to supply air from the stalk and leaves to the submerged rhizomes and roots.
Figure 4. Example of Aerenchyma tissue from a species of rush. Photo Credit: Wikipedia.org
Consequently, this makes cattails very buoyant and gives it the ability to float. This buoyancy sets the stage for the creation of floating cattail mats. Mats can sometimes be up to 3-feet thick and over ten acres in size.
Unfortunately, once a mat manifests itself and is free-floating, the mat can continue to grow out into even deeper water. So, how does it survive without soil? Cattails can survive in open water because their roots are so efficient at absorbing nutrients, they can strain out the nutrients they need from the water they are in. This process is very similar to how plants like tomatoes are grown using hydroponics.
Figure 5. Floating mat threatening lake shore residents dock and watercraft on Rainy Lake, MN, USA. Photo Credit: Jamie LaDuc, NPS
At a certain point, the cattail mat becomes so massive that with the right environmental event, like a high-water period, the buoyancy pressure of the mat can sever the mat’s connections to its rooted anchor points and allow the mat to float freely within the water body.
A free floating mat causes two main issues: 1) depending on the size of the mat, it can create navigational hazards or damage shoreline infrastructure like personal boat docks (Fig. 5); and 2) a floating mat is a great way for the invasive hybrid to spread to other non- infested areas and establish, starting and establish, starting the cycle over again.
For example, in 2017 a ~6-acre floating cattail mat broke free from its anchors in Irwin Bay on Kabetogama Lake in Voyageurs National Park (Fig. 6) and bounced around for almost a year. The floating mat traveled over 13 miles before park staff, local business owners, and residents used boats to push it into Rudder Bay and trap it there over winter (Fig. 7). In 2018, contractors, using specialized machines, destroyed the mat and removed the material for disposal.
Figure 6. Satellite imagery showing the movement of a single cattail mat on Kabetogama Lake
WHAT IS VOYAGEURS NATIONAL PARK STAFF IS DOING TO DEAL WITH THE ISSUE?
These are the exact problems park staff are facing here at Voyageurs National Park where pristine border water wetlands have been invaded by hybrid cattail. Recent studies confirmed our worst fears that most of the cattail found along the shores of the main lakes in Voyageurs National Park are the invasive hybrid. The aggressiveness of these invasive cattails has resulted in the large hybrid cattail stands now seen in the park. We have identified over 500-acres of the invasive hybrid that now exist within the parks boundaries and that continue to spread (Fig. 8). Not to worry though, we are fighting back.
Figure 7. Irwin Bay mat that floated through Kabetogama Lake and was trapped in Rudder Bay in 2017. Photo Credit: Bryce Olson and Reid Plumb, NPS
In 2016, park staff began a new project to deal with the expanding cattail problem. Many techniques are available to deal with invasive plants. Herbicide is often the first that comes to most people’s mind, but the park has some unique challenges. While herbicide is no doubt a cost effective and efficient means to deal with invasive plants, the lakes within Voyageurs are designated as “Outstanding Resource Value Waters” by the State of Minnesota.
Figure 8. Map highlighting ~500 acres of known hybrid cattail infestation in Voyageurs National Park, MN, USA. Photo Credit: Bryce Olson, NPS
Regulations stemming from this statute prohibits the use of herbicides within the water system. Adding additional challenges, water levels on the large lakes (Rainy, Kabetogama, Sand Point, Namakan) are regulated by the International Joint Commission which sets upper and lower bounds (rule curves) to which dam operators maintain the water levels throughout the year. Water level manipulation is often critical to the effectiveness of many cattail control methods further complicating viable cattail control options. Because of the lack of scientific information to overcome these complexities, park staff had to get creative to develop a multiyear cattail removal and wetland restoration plan. As a result of the plan’s complexity and the unknowns associated with this effort, park staff are approaching this in an “adaptive management framework”. The adaptive management framework of “learning by doing,” allows staff to meet resource management objectives while simultaneously learning, adapting, and subsequently guiding future management.
For serious infestations where floating mats have formed, we use contractors and specialized equipment called “cookie cutters” (or swamp devil) and harvesting barges to chew up the mat, roots and all, and collect the chewed-up material to dump in spoil areas. This method has shown to be very effective at killing the hybrid cattail and removing the floating mat portions with almost a 100% kill rate. The main disadvantages to this method are that it can be expensive and it generates a large amount of spoil material that we must deposit somewhere. We also cannot use this method in every situation due to variability in water depth or presence of bedrock.
Underwater cutting is a promising treatment method that is less costly than the heavy equipment we use for floating mats. Cattails use their specialized aerenchyma tissue to “breathe” in their aquatic environments and cutting cattail stalks underwater restricts their air supply and, if done at the right times of the year, effectively drowns the cattail root and rhizome. However, this method isn’t without its disadvantages as well. This method is labor and time intensive and may require follow up treatments. Further, it is only effective where cattails are still rooted to the substrate but their roots are far enough below the water level to where they cannot grow their “snorkel” back fast enough. Despite these limitations, this method is still an effective treatment method for small treatment areas or for managing cattails in areas treated by the mechanical means described earlier.
Unfortunately, the invasive hybrid is also well adapted at invading wetland areas that are not fully submerged by water such as shorelines. This is a tricky area to treat as staff cannot remove it using heavy machinery or cut it under the water to drown it. Like the principle of Judo, where you use your opponent’s weight against them, we use the spoil material from the removed mats to kill other patches of cattail. How does that work you ask? It’s basically the same principle as using grass clippings as weed barrier in your garden to. We pile the spoil material along the shoreline and use a special machine with a rototiller on the front to pull back and spread the material in a thin layer over existing live hybrid cattail (Fig. 11). The material creates a barrier that the cattail has difficulty growing up through. We then reseed with native wetland plant mixes and reestablish a native plant shoreline community.
Figure 11. Using spoil material from removing floating cattail mats to create a barrier over cattail that we were unable to remove with heavy machinery, killing the cattail and re-seeding the treated area to establish a native lakeshore plant community. Photo Credit: Bryce Olson and Reid Plumb, NPS
We have learned a lot over the last 5 years about which treatment methods work best under some specific conditions. But we still have lots to learn where we do not have the conditions for the treatments previously mentioned. In these cases, we are using multiple alternative treatments that do not aim at killing the plant, but rather help native species compete with the hybrid cattail and increase plant diversity. We are using controlled burning and winter/ summer surface scrapes to remove the canopy that cattail stands produce which shade out competing natives (Fig. 12); much like clear cutting. Where we have used these treatments, we have found substantial increases in plant composition and diversity. However, because these treatments do not kill the underlying rhizome, these results will most likely be short lived and will need continued management to maintain plant diversity.
WHAT CAN YOU DO?
The best thing anyone can do is to stop or slow the spread. Even though the invasive and hybrid species have been found over most of the United States, pristine native cattail stands still exist, primarily in remote areas far away from roads and human development.
Both broadleaved and narrow leaved cattail species have the characteristic sword-like leaves originating from a tall horizontal stem, primarily differing in their leaf width, flower size, and flower spike separation. Identification of the hybrids is extremely difficult based on external characteristics of the plants alone, as they have considerable overlap between the two parent species in terms of width of leaves or shape and size of the flower heads. A good rule of thumb: most cattails that exist in natural or created wetlands in Minnesota are likely hybridized and you cannot tell them apart simply by looking at them.
If you are creating a backyard pond or water garden, consider using other native emergent plants such as softstem bulrush (Schoenoplectus tabernaemontani), broadleaf arrowhead (Sagittaria latifolia), giant burreed (Sparganium eurycarpum), or sweet flag (Acorus americanus) instead of cattails.
If you are set on adding cattail to your waterscapes, make sure you research the plant provider and buy native cattail (Typha latifolia). It may even be worth giving the provider a call and asking how they determine if their stock is the native variety. The best-case scenario is that they genetically test their native stocks for purity.
If you already have an established pond or water garden and have cattail that you would like to remove, there are a few ways to do it. The easiest and most effective would probably be a water “safe” herbicide. For those folks that would rather try non-herbicide removal methods, we would suggest cutting the stems as low as you can under the water in mid- to late-July. Cuts should ideally occur as the plant is forming seed heads. This will set the plant back while it is expending the most energy during reproduction. You may need to repeat cuts within the same year if you see the spikes emerge from the water’s surface. Results will vary depending on water depth but over a few years it should be well knocked back if not completely gone. If you can manipulate the water level and raise it, consider raising the water level as high as possible right after you cut the cattail. This should increase the effectiveness of this method. Another option is trying to dig up the rhizome and roots but that is messy and labor intensive.
If you have lakeshore property and are thinking of removing cattail, be advised that the State of Minnesota requires a permit for any aquatic plant management. If removing cattails, please follow the states guidelines for transporting uprooted cattails for disposal. Roadways often act as superhighways for the spread of invasive species. If possible, let the cattails decompose on high ground near the removal site, or if you must transport them, do your best not to disperse seeds or rhizomes along the way.
Figure 12. Illustration of how fire removes dead canopy material created by cattail and helps native plants compete. Photo Credit: Darren Kuropatwa (Left), Steve Windels, NPS (top right) Allen T. Chartier (bottom right).
Project support
Project successes, accomplishments, and its continuation would not be possible without the funding and support from our partners and collaborators. Major funding for this project was provided by the Outdoor Heritage Fund, as appropriated by the Minnesota State Legislature and recommended by the Lessard-Sams Outdoor Heritage Council (LSOHC), as well as the Minnesota Environmental and Natural Resources Trust fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR).
Additional funding was provided by Voyageurs National Park, National Park Foundation, Initiative Foundation, Voyageurs Conservancy, Duluth Superior Area Community Foundation, and the U.S. Environmental Protection Agency. We would like to thank the MN Department of Natural Resources, Kansas State University, and the International Joint Commission for their continued collaboration and support of our project.
