Are Common Cattails Typha latifolia Really an “Invasive Native Species?”

Summary 

If common cattails, Typha latifolia, can be used to treat wastewater and restore degraded marshes and wetlands, then human perceptions of this native invasive species should change. Although Typha spp are indeed native to North America and much of the world, they are often considered invasive due to their tendency to form large monocultures, something that has been on the increase over the last century in North America. Cattails are unique in adapting to high nutrient and metal concentrations without suffering negative effects. In fact, Typha spp has been shown to increase growth under conditions most other plants find toxic. They also remove toxins and excess nutrients, cleaning the water in the process. Humans have drained so many wetlands, more than 90% in most urbanized areas. The few wetlands that remain are almost always subjected to drastic changes in both water quality and quantity. As a result, we have created conditions for the cattail, and very few other plants, to thrive in. Perhaps instead of treating the cattail like an invasive weed, we should accept the fact that the cattail monoculture issue is simply a natural response to the unnatural degradation of our wetlands. Then we could instead focus on letting the cattails do their work of removing toxins. Simultaneously we would need to work at restoring balance to the ecosystem. If you would like to learn more, please continue reading.   

Description and Distribution of Typha latifolia and Typha spp. 

Typha latifolia, the common cattail, is a native emergent aquatic species found in wetlands, marshes, ditches, ponds, and lakeshores throughout most of the world. It lives in every Canadian province and territory and south throughout the entire continental USA and Mexico. It is also found worldwide in Britain, Eurasia, Africa, India, New Zealand, and Australia. T. latifolia is a herbaceous perennial with long slender green stalks over 1 m tall topped with terminal round flower spikes. The flower spikes have male flowers on top and dense persistent female flowers beneath that are greenish when new but turn characteristically brown and fuzzy when mature. Basal leaves are thin with parallel veins that run their entire length of more than 1 m. The cattails reproduce by seeds but also readily reproduce vegetatively by clonal spreading of their thick underground roots.  

Typha angustifolia and Typha x glauca, a hybrid of T. latifolia and T. angustifolia, are two other common native cattails in North America. The other two cattails are easily separated in the field by T. latifolia’s male and female spikes that usually have no gap between them and its very robust dark brown female spike at maturity. T. angustifolia and T. xglauca’s narrower leaves and the gap between its female and male spikes differentiate them from T. latifolia. T. latifolia is also more tolerant of a wider range of conditions from tropical to cool temperate in both humid and dry climates from sea level up to 2125 m in elevation. The other two species are found at lower elevations and latitudes.

The Use of Emergent Aquatics in Constructed Wetlands

Emergent aquatics, particularly Typha latifolia, have been shown in multiple studies to be effective biofilters that can help remove excess nutrients and toxins from wastewater. Emergent aquatics are important in wastewater treatment wetlands because they help stabilize the plant beds, provide filtration, surface area for microbes, slow the speed of currents, aid in sedimentation, and increase the contact time between runoff and plant surface area. Furthermore, the turnover of roots allows for better aerobic conditions and water penetration into the soil. The roots also release organic compounds that provide a food source for denitrifying microbes that are important for removing Nitrogen.

When it comes to removing toxins or excess nutrients from wetlands, laboratory studies have shown that cattails can accumulate high levels of Copper, Nickel, and Iron in their leaves and especially their roots. Those same studies found that growth was actually stimulated at moderate levels of Copper that many plants find toxic. Further studies by the same authors on Nickel and Iron showed no toxicity with concentrations five to six times higher than that of Copper. These studies show that cattails are highly tolerant of excess metals and could be a valuable tool in remediation.

The removal rates of excess nutrients and pollutants from wastewater predictably vary under the varying environmental conditions outside the laboratory. But this is useful in that constructed wetlands can be designed to optimize targeted pollutants by using a different construction design. For these reasons and its widespread native distribution, Typha latifolia is a common plant used in constructed wetlands designed to purify wastewater or as a secondary treatment for municipal sewage treatment plants. They are abundant, adaptable, provide structure, and clean the water. They truly are miraculous plants when it comes to their use in constructed wetlands.

The Invasiveness of Typha latifolia Cattails

Some people have concerns about using cattails in wetland restoration projects because they are often considered to be an invasive species. Cattails may appear invasive due to changes in water levels, wildfire suppression, excessive nutrients, or metal input which all favor cattail growth at the expense of other species. This can result in large monocultures of this native species. Typha’s ability to clone and grow rapidly also contributes to its superior competitive ability under altered environmental conditions. If, however, the wetland is a high-quality natural area, the cattails generally exist as scattered patches of plants with open water and numerous other species. This suggests that it is wetland degradation and not the cattail itself that is forming the monocultures.

In the case of wastewater treatment wetlands designed specifically to handle contaminated water, then the invasiveness of cattails is not an issue. Most other species would not be able to survive in the conditions of constructed wastewater wetlands anyway. Typha latifolia, on the other hand, will flourish and clean the water at the same time as providing a habitat for birds and invertebrates that use the cattails for nesting and reproduction.

This all suggests that the cattail itself is a successful opportunistic species that can adapt to a wide range of adverse conditions. While this itself does not make it invasive, it does suggest that the cattail’s inherent ability to tolerate adverse conditions is what is creating the monocultures. We are the ones who are degrading our wetlands, so we are creating the conditions in which cattails can sometimes create monocultures.

Removal of Cattail Monocultures To Restore Biodiversity

Studies of the physical removal of some of the cattails in monocultures have shown a marked increase in biological diversity in both the soil and water. These same and other studies have also shown a noticeable increase in birds, muskrats, and invertebrates. Other studies with draining and burning showed that while draining alone increased Typha cover, it also increased species diversity. If you use draining along with summer burning, it will help reduce Typha dominance while releasing nutrients and stimulating the growth of other species. This draining and burning process, because it also mobilizes nutrients, may help deal with the excess nutrient load that created the monoculture in the first place. In the case of excess metals, however, the cattails and their roots should simply be periodically removed and disposed of, removing the toxins from the system while promoting biodiversity. These methods will all work if we have eliminated or reduced the source(s) of pollutants or water changes. This may be an effective way to quickly restore the diversity that used to exist in these marshes before human disruption turned them into monocultures.

Conclusion:

In summary, Typha latifolia can be very useful both in restoration projects and in wastewater remediation. The invasiveness of cattails is not an issue if we address the disruption and pollution of our wetlands. In areas where they already are monocultures, if we correct or mitigate the source of degradation, those wetlands could easily be restored to recreate thriving and biodiverse wetlands. Furthermore, using cattail monocultures in wastewater treatment wetlands is beneficial since the cattail is very effective for wastewater treatment and few other plants will survive in those conditions. Finally, perhaps it is our perception that is what really needs to change. Instead of treating cattails like an invasive species, we should recognize why they may form monocultures. We should take responsibility for it rather than blaming this native species and trying ineffectively to control it. Instead, we should let it thrive and do its job while we work to create cleaner wetlands with less pollution and water stresses. After we have done our part either in creating cattail treatment wetlands where needed or by reducing or eliminating sources of degradation, then we can look at addressing the cattail monocultures through passive or active restoration processes.

If you want to learn more about native plants in North America, Check out my new Native Plant of the Week Blog where each week I will focus on a different native plant. You can learn how to identify it, where it is found, its conservation status, its traditional uses, and ethical wildcrafting.

And if you want to learn more about invasive species, what they are, and why we should be concerned, check out What are Invasive Species and What Should We Do About Them? Also, check out my newest blog category on Invasive Species of North America where each week, I will describe a different invasive species in North America and what we can do to help control it.

References and Resources

Ducks Unlimited. Managing your Restored Wetland. Online publication http://www.ducks.org/media/Conservation/GLARO/_documents/_library/_landowner/Freshwater_WL_Mgt.pdf

Grace, JB and JS Harrison, 1986. The Biology of Canadian Weeds. 73. Typha latifolia,Typha angustifoia and Typha xglauca. Can. J. Plant Sci. 66: 361-3’79.

Green E.K., and S.M. Galatowitsch 2001. Differences in wetland plant community establishment with additions of nitrate-N and invasive species (Phalaris arundinacea and Typha xglauca). Department of Horticultural Science, University of Minnesota. Published by NRC Research Press February 12,2001.

Keeler, Kathleen, 2015. Visiting Alberta–Cattail Marshes and Flyways. The Wandering Botanist. http://khkeeler.blogspot.ca/2015/12/visiting-alberta-cattail-marshes-and.html. December 27, 2015.

Motivans K. And S. Apfelbaum. 1987. Element Stewardship abstract for Typha spp. North American cattails. The Nature Conservancy. October 2007.

Taylor, Gregory J and A. A. Crowder, 1983. Uptake and accumulation of heavy metals by Typha latifolia in wetlands of the Sudbury, Ontario region. Canadian Journal of Botany 61: 63-73.

Taylor, Gregory J and A. A. Crowder, 1984. Copper and nickel tolerance in Typha latifolia clones from contaminated and uncontaminated environments. Canadian Journal of Botany 62: 1304- 1308.

USDA Plant Guide. Broad-Leaved Cattail Typha latifolia. USDA NRCS National Plant Data Center & Idaho Plant Material Center.

Wetlands International, 2003. The use of constructed wetlands for wastewater treatment. Wetlands International, Malaysia Office, First Edition 2003.

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