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The Achilles Heel of Reed Canary Grass

August 8, 2019

It’s a depressing sight. We’re looking at a sea of reed canary grass in what was once a vibrant sedge meadow and wet prairie. Like nearly all the remaining wetlands in southern Wisconsin, nearby agriculture and development altered the area hydrology, setting the stage for the invasive species reed canary grass to roll in like a malignant cancer smothering out all native life. The landowner moans, “Restoring this wetland is hopeless isn’t it?” I hold my answer and press forward in the shoulder-high grass, focused on a thin spot in the reed canary grass ahead. We arrive at the spot, I dig around in the thick grass thatch, turn to the landowner, smile and say: “There’s hope.”

    

Partially hidden in decades of reed canary grass thatch, we find thin blades of the native hairy-fruited sedge (Carex trichocarpa) still holding on like a small band of resistance fighters against an invading army of superior numbers. Here is your hope, I say to the landowner, pointing at the sedge. We “arm” the sedge by burning off the grass thatch and applying selective herbicides as conditions allow.

 

Reed canary grass is one of our worst invasive species of wetlands. It creates complete monocultures, eliminating native plants and hence the native insects, butterflies, birds, amphibians, reptiles and other native creatures that depend on a functional native ecosystem. It can survive flooding and thrive in upland soils. It reproduces aggressively through underground runners (rhizomes) and from abundant seed production. In fertile soils, it can grow to nine feet tall and produce copious vegetative mass. It’s this feature that makes it attractive to agriculture; some farmers still plant it as “marsh” hay. Very few native plant species can survive the dense growth and thick thatch of reed canary grass.

 

Except its Achilles heel, the native hairy-fruited sedge, which has proven very useful in wetland restorations due to its amazing ability to resist and compete with the invader.

 

Like canary grass, hairy-fruited sedge is rhizomatous. It forms dense stands of “medium” green foliage that is very attractive. In fact, I recall one landowner commenting “It’s so inviting, you just want to lie down in it.” But unlike reed canary grass, its growth form and minimal thatch build up allows for a lot of space at ground level, making it paradise for amphibians, birds and other critters to move around while under the cover of the sedge foliage.

 

Many native insects use hairy-fruited sedge, perhaps the most charismatic being the two-spotted skipper. I routinely flush species such as pickerel frogs and sora rails while walking through sedge stands. Waterfowl, such as mallards, use the dried sedge as nesting material. Whitetail deer routinely hide their newborn fawns in the thick sedges. Even somewhat clumsy critters such as turtles and toads have no trouble migrating through the sedge on their way to breeding grounds. In summary, the use of hairy-fruited sedge as a deterrent to reed canary grass can greatly facilitate the return of an amazing amount of native wetland wildlife diversity.

 

Here’s the basics on what to do: Use prescribed fire to remove the thick, smothering reed canary grass thatch and allow suppressed native plants a chance to grow. Where appropriate, grass-specific herbicides can weaken the reed canary grass, but doesn’t harm nearby sedges or forbs (flowers), allowing existing sedge stands to expand quickly. Hairy-fruited sedge transplants very well, too. For example, we typically remove a 4-inch diameter plug and plant it in a thick patch of reed canary grass. I’ve also had luck establishing it from seed.

 

In stream restorations, it’s typical to flatten the steep banks by removing eroded soil that has accumulated over time because of poor agricultural practices. We plant hairy-fruited sedge plugs in the newly exposed soil to prevent canary grass from taking over, and then monitor vigorously for any invasion.

 

After a few years, the sedges grow rapidly along the streambanks, effectively armoring it against high-water events, resisting canary grass and facilitating the return of native wildlife.

 

We’ve used this technique in reconstructed ponds by transplanting the sedge plugs into the wet clay at the water’s edge. The sedges expand up the banks, keeping out reed canary grass and cattails. Lake sedge (Carex lacustris) also works well in this setting. Frogs (and their predators) expand exponentially once these sedges are in place along the ponds’ edge.

 

With the use of fire, careful use of selective herbicides, woody control (shading is another disturbance that favors reed canary grass) and hairy-fruited sedge available on site, I have witnessed vegetative cover go from 100% reed canary grass down to approximately 35% over a six-year period. The difference is visually dramatic, as is the return of wetland critters.

 

Like all restoration projects, it’s important to set reasonable expectations. Some areas will likely always be trouble spots for reed canary grass, making it important to focus efforts in areas with the best chance of success and then expand out from there. Also, be prepared to annually perform management activities indefinitely in order to maintain a heathy ecosystem.

 

I have used other native sedges, such as the previously mentioned lake sedge and woolly sedge (Carex pellita) with success against reed canary grass, but none has been as successful as the hairy-fruited sedge.

 

Some may argue the aggressive nature of hairy-fruited sedge excludes other native plants. Well, yes, but it’s a question of what you want. An aggressive native plant that pumps life back into a native ecosystem or a non-native invasive species, reed canary grass, which completely destroys it. It’s an easy answer. And, there is another nifty native plant, marsh betony, which weakens hairy-fruited sedge, allowing niche spaces for a lot more native plant species. I’ll write more about marsh betony in a future post.

 

There are so many things we don’t understand and can’t control in our restoration efforts, making it crucial to hold onto the one thing we can – hope!

 

Photo gallery below:


The photo below shows a stream restoration completed in 2012. While a bit hard to see from this late-summer photo, the banks are completely covered in hairy-fruited sedge. The only reed canary grass present is an occasional clump right next to the water's edge. The tall vegetative foliage encloses much of the water's surface keeping the water cool for trout and other wildlife. The submergent plant in the water is water speedwell. Other plant species on the bank include great Angelica, soft stem bulrush, fowl manna grass, great blue lobelia, Canada milkvetch, golden Alexanders, prairie cordgrass, common ironweed and Canada goldenrod. 

The photo below shows a large stand of hairy-fruited sedge (lower half of picture) that was once solid reed canary grass. You can see the edge of the sedge clone at the left side of the picture near the treeline/houses. The thin strip of tan vegetation is reed canary grass. The purple/magenta colored flowers are wetland Joe-pye weed. Other species present include sawtooth sunflower, marsh hedge nettle, tussock sedge, woolly sedge and lake sedge.   

The photo below shows the dark "V" at the leaf sheath (area in focus in the center of the photo) identifying hairy-fruited sedge. 

 

 

 

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