Cattail Invasion in North American Wetlands: What Four Decades of Research Show

U.S. Geological Survey Fact Sheet 2019–3076, February 2020. By Sheel Bansal and Brian Tangen (USGS), Shane Lishawa (Loyola University Chicago), Sue Newman (South Florida Water Management District) and Douglas Wilcox (SUNY Brockport).

Cattail (Typha) is an iconic wetland plant found worldwide. It spreads its seed on the wind across great distances, grows fast and large, and forms dense stands in marshes, ponds, lakes and along rivers — and quickly takes over disturbed, waterlogged places such as roadside ditches and the edges of stormwater ponds. Those stands change the plants and animals, the nutrient cycles and the water of a wetland.

In recent decades cattail has become more widespread and abundant in North America, because people have altered natural water cycles and added nutrients, and because aggressive non-native and hybrid cattails have sped its spread. Managers often fight it widely, with short-lived or weak results. Yet cattail also has uses, from cleaning up pollution to biofuel.

No one had pulled the research together, so a large team reviewed four decades of work from more than 650 references (Bansal and others, 2019). This fact sheet summarises the review.

How cattail thrives

North America has broadleaf cattail (T. latifolia) and southern cattail (T. domingensis), both native; narrowleaf cattail (T. angustifolia), probably from Europe; and their hybrid (T. × glauca), which is especially invasive thanks to hybrid vigour — it gets the traits of both parents.

• Seeds. In late summer one flower head can release up to 700,000 wind-borne seeds, which can travel more than 0.6 mile (about 1 kilometre).
• Size and speed. Once established, cattail grows fast, gets big — taller than 6 feet (about 2 metres) — and spreads rapidly.
• Built for water. An internal air-ventilation system carries oxygen to its rhizomes (roots), which also store food over winter for a fast start in spring.

(A) A dense stand seen from where a seedling would sprout — little light gets through. (B) A leaf cross-section showing aerenchyma, the air channels that carry oxygen to the roots. (C) Rhizomes, which let one plant spread and store food for spring. Photos: Olivia Johnson and Jacob Meir, USGS.

Why it invades

Cattail has limits that normally keep it in check. It needs saturated or flooded soil under less than 6 feet (2 metres) of water, so it suffers when water stays high or low for long periods (more than 2 years), and it takes up nutrients poorly in nutrient-poor water, where native plants can outcompete it. But long-term changes to natural water levels, together with fertiliser runoff from farms, have tipped the balance. The review highlights three regions hit hard: the Laurentian Great Lakes, the Prairie Pothole region and the Florida Everglades.

What invasion does

• Wildlife. Dense stands push out diverse plant communities, removing plants that feed water birds, wildlife and pollinators, changing the structure of the vegetation and piling up dead plant litter. Simpler habitat means fewer good nesting places for water birds and harm to invertebrates and fish, key food for other animals. Invaded wetlands may also dry faster and break up, hurting animals such as amphibians.
• Farming. Cattail competes with flooded crops such as rice, clogs irrigation canals and drains, and gives roosts to flocks of blackbirds that damage crops such as sunflower.
• Nutrients and climate. Invaded wetlands cycle nitrogen and phosphorus faster, and their soils hold much more nitrate, ammonium and phosphate. Cattail stands store a lot of carbon in the soil — a climate benefit — but also raise emissions of methane, a powerful greenhouse gas, by feeding methane-making microbes and venting the gas through rhizomes and stems.

Blackbirds in the Prairie Pothole region. Huge flocks roost in cattail for cover and fly out to feed on sunflower and corn; damage in North Dakota alone was estimated at nearly $4 million in 2010. Thinning cattail breaks big roosts into many small ones, easing local crop damage and improving the wetland.

What cattail is good for

• Indigenous peoples use parts of the plant for food, medicine and goods such as woven baskets and mats; it also feeds and shelters animals — muskrats build dens with it.
• Cleaning water. Cattail removes metals and nutrients — it grows fast, draws elements from soil, tolerates contamination and keeps most harmful elements in its roots. Harvesting it removes them for good.
• Products. Biofuels and fuel pellets, compost, livestock bedding, soil improvement and carbon storage.

Biomass harvest. Compared with crops such as corn, cattail for fuel: grows in water, not on farmland; grows fast; is not a net source of carbon; usually needs no tilling or planting; and its harvest generally improves wetlands and removes excess nutrients. At Netley-Libau Marsh and Pelly's Lake in Canada's Lake Winnipeg watershed, harvesting removed large amounts of nitrogen and phosphorus from the Red River and restored wetland habitat — research that guided large-scale phosphorus removal. Burning it as fuel also means less coal.

Managing it

Controls include herbicides, burning, flooding, mowing, crushing, replanting and grazing. After decades of research, lasting control is still hard, and successes often fade: mowing and herbicides rarely work well because the extensive rhizomes let stands regrow fast. Usually several actions are needed, timed to the plant's life cycle and season, weighing the trade-offs for wanted plants and animals. Examples range from experimental flooding at the USGS Northern Prairie Wildlife Research Center in North Dakota and aerial herbicide in the northern Everglades to planned burns at Agassiz National Wildlife Refuge in Minnesota, biomass harvesters in Michigan's Cheboygan Marsh and replanting at Cowles Bog in Indiana Dunes.

What we still need to know

• How cattail — especially the hybrid — will spread under climate change and changing nutrients and water levels.
• Cattail genetics, and where it grew in the distant past (paleoecology), to understand what drives invasion.
• Effects on fish, invertebrates, amphibians and pollinators, not just plants and birds; links to nitrogen, phosphorus and carbon cycling; and how to break the feedback loop between altered water, nutrients and invasion.
• When invasion warrants control, and whether control's benefits outweigh harm downstream — studied across many regions, at scales managers use, for long enough to see lasting results.

Sources

• Bansal, S., Tangen, B., Lishawa, S., Newman, S., and Wilcox, D., 2020, A review of cattail (Typha) invasion in North American wetlands: U.S. Geological Survey Fact Sheet 2019–3076. https://doi.org/10.3133/fs20193076 · https://pubs.usgs.gov/publication/fs20193076
• Bansal, S., and others, 2019, Typha (cattail) invasion in North American wetlands—Biology, regional problems, impacts, ecosystem services, and management: Wetlands, v. 39, no. 4, p. 645–684. https://doi.org/10.1007/s13157-019-01174-7
• Figure 1 and the management examples come from the fact sheet's PDF. Its other photographs are credited to universities, state agencies, a water district and stock sites, and are not reproduced here.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.