A big topic of conversation at this year’s Grassland Restoration Network (GRN) workshop had to do with designing seed mixes to combat potential invasive plant problems. When converting cropland to prairie vegetation, the first few years of establishment are sometimes a race for dominance between prairie plants and invasives. Once a strong native plant community becomes established, it is more difficult (but still possible) for invasive plants to become dominant, so those first few seasons are critically important. Over the years, a number of people have tried using extra high seeding rates of various native plants to see if those natives could help stave off invaders. In an ideal scenario, a high abundance of some showy wildflower would outcompete invasive plants but allow other native plants to establish. Nice, right? Lots of pretty flowers during establishment, no invasive species to worry about, and a nice diverse prairie community in the long run.
I first heard about this idea at the 2004 North American Prairie Conference. In one of my favorite presentations of all time, Shawn Schottler of the Science Museum of Minnesota compared various plant species to celebrities. As he described his experiments, he said he was trying to find Chuck Norris plants (tough good guys) that could fight off Mike Tysons (aggressive invasives) while still allowing Patsy Clines (less competitive natives) to establish. As I recall, he was having some luck with Chuck Norris species such as black-eyed Susan (Rudbeckia hirta), wild bergamot (Monarda fistulosa), and others. At this year’s GRN workshop, Jack Norland of North Dakota State University described recent results of some similar experiments on U.S. Fish and Wildlife restoration projects. The “spike” treatments they used consisted of ultra high seeding rates of species such as plains coreopsis (Coreopsis tinctoria), purple prairie clover (Dalea purpurea), Canada wild rye (Elymus canadensis), and others. His data showed Canada thistle to be much less abundant in spike treatments than in the controls.
Interestingly, we’ve had some accidental experience with this topic here in our Nebraska Platte River Prairies. During the drought years of the early 2000’s, some of our prairie plantings ended up with lots and lots of Canada wild rye. In some cases, the species was so abundant that our plantings looked like wild rye monocultures. We weren’t the only ones. Prairie Plains Resource Institute had plantings that looked much the same during those years. There was some hand wringing about whether or not the plantings had failed, especially given the drought conditions at the time, but Bill Whitney of Prairie Plains assured us that it wasn’t a big deal. He was right, as usual. The plantings eventually emerged from their wild rye phase and turned into very nice prairies. In fact, our site that had the “worst” wild rye infestation is now the showiest (in terms of big colorful wildflowers) prairie we have. I’m not sure the wild rye helped suppress any invasive species, but a high density of wild rye plants didn’t seem to keep Patsy Clines from eventually thriving.
Spike treatments/Chuck Norris species/etc., are really just variations on the idea of using a cover crop – planting something intended to establish early and then fade away (mostly or completely) as the desired vegetation takes hold. In some places, cover crops are very useful in agricultural systems as a way to prevent soil erosion and loss of fertility, suppress weeds, and/or preserve soil moisture. It seems logical that they would also help with prairie restoration establishment. In fact, I recently talked to someone with the Natural Resources Conservation Service (NRCS) in north central Nebraska who says their best successes in restoring sandhill prairie come when they use a cover crop of millet.
On the other hand, I remember a GRN workshop about five or six years ago when we had a group discussion about our experiences with various cover crops. Participants from across the Central U.S. seemed to reach consensus that cover crops were as likely to be counterproductive as helpful to prairie restoration efforts. This seems to conflict with the successes seen by people like Shawn Schottler, Jack Norland, and others. Why the differences?
Part of the issue is certainly that we’re still experimenting with different species, and still have a lot to learn. Beyond that, though, anyone who has spent many years restoring prairie knows that establishment results can be very difficult to predict, even within the same site. Just when you think you’ve got something figured out, your next planting turns out completely unlike what you’d expected. Those kinds of inconsistencies, combined with differences in site attributes such as soil texture and fertility, rainfall, and latitude make it almost impossible to come up with restoration recommendations that apply everywhere. In fact, if we’ve learned anything through the Grassland Restoration Network, it’s that it’s important to start big projects by doing some small experimental plantings to see what works best in that place before investing in larger scale work.
Clearly, the idea of “spike” treatments and similar strategies hold a great deal of promise if they fulfill their promise of preventing invasives while facilitating establishment of diverse plant communities. However, since it’s also clear that successful strategies from one site don’t always translate well to others, we may each have to find our own formula for success. Hearing about Dr. Norland’ experiments in the Dakotas has inspired us to do some more experimentation here. Maybe we can find a few Chuck Norris species to keep the peace in our Platte River Prairies.
If you’ve had positive or negative experiences with cover crops in prairie restoration, or have found your own Chuck Norris of the prairie, please share what you’ve learned in the comments section below. Thanks.
P.S. You may have seen or heard some of the many Chuck Norris jokes out there that play on the idea that he is seemingly invincible. My 14-year-old son likes to share them with me now and then. A few of my favorites are:
Chuck Norris doesn’t wear a watch. He decides what time it is.
Chuck Norris makes onions cry.
There used to be a street named after Chuck Norris, but it was changed because no one crosses Chuck Norris.
When Chuck Norris does a push up, he isn’t lifting himself up, he’s pushing the Earth down.
A bulletproof vest wears Chuck Norris for protection.
Great illustration of learning to wait and not expecting glorious results immediately. Beautiful. I may try some of your ideas in my yard. I live in the city but still would like a natural look.
Not exactly a cover crop comment, but an observation on the value of rye species in suppressing invasives. Where I have clumps of Virginia wild rye growing in my oak savanna, it seems to keep the reed canary grass out. (The roadsides in our area have heavy infestations of rcg.)
In our woodlands, the Virginia wild rye is also outcompeting Wintercreeper (Euonymus fortunei) and lesser celandine (Ranunculus ficaria); it does not eliminate them, but is helping to keep the invasive species from taking over completely. Unfortunately, it doesn’t leave a lot of openings for other native species to get a foothold, either.
This coming from a complete restoration novice… is it possible to selectively and strategically plant ‘Patsy Clines’ after a successful crop of Canada Wild Rye is established? Or do you need to plant the seed mix at the same time and hope that eventually the more showy plants will emerge. As a landscape architect, the thought of establishing desirable monocultures and then strategically planting new species seems like it might be a good method. This would probably be pretty labor intensive to transplant, but could one spread new seeds? Another question is what role does the existing seed bank play?
Thanks so much for your blog – extremely informative!
Shawn, good questions. Here in Nebraska, it’s usually much more effective to broadcast what we want for species all at once rather than in multiple stages. Planting in the second year presents some challenges such as getting the seed to the soil because there is vegetation in the way and that vegetation can also shade out young seedlings. Our experience is that it’s better to start everything at once, though in wetter places, that might not hold as true. In terms of seed bank, in most crop fields, the seed bank consist mainly of annual “weeds”, rather than Patsy Clines…
This is a very good question! The short answer is yes, you can wait to plant certain Patsy Cline spplecies later via interseeding, but you have to know your species and what timing and planting method works better to foster establishment. Oftentimes, simply due to the usual limitations we have with grant funds and other resources, we plant everything together. However, the most relevant situation for partial/delayed planting is when you plan to use certain herbicides to kill targeted invasives. We’ve contemplated this in southern MN when we want to plant natives and use Milestone to kill Canada thistles during the establishment period for the seeded natives. You essentially plant a mix of species that tolerate Milestone and then plant the more sensitive species after all the chemical work is done (can take several years). I’d say the biggest challenge to a delayed approach is creating sufficient niche space for the Patsy Clines at seeding time. Typically, the best time is after a good, thorough Rx burn (seed as soon as possible after the burn is over). The ash and open ground make great helpers. I’ve done prairie interseedings with good success, but not all species lend themselves to it the same way.
in western Oregon I like to pair a fast germinating annual with a slow-to-germinate perennial. Most of our perennials need 3 to 4 months of winter weather to break dormancy, which means there is a long window for non-natives to sneak in. I like using annuals that burn down completely by June, which gives the slow growing perennial the rest of the summer window to establish. The fast burn species I use in Oregon probably aren’t appropriate for the mid-west, but include Collinsia grandiflora, Lupinus bicolor, and Plagiobothrys figuratus.
Sorting out the interactions between species to determine which natives can reduce invasives sounds like a good use for factorial experiments. The plus side is a researcher will get to use the statistics they learned in grad school. The down side is we won’t know the results for a couple years.
I don’t get out or stay in to watch too many movies, but the movie that I know Chuck Norris from is the one where he fights Bruce Lee, and is the bad guy and gets beat, but I digress…
I like canada wild rye as a cover crop, can not be beat for Indiana prairie restoration.
Experience from cropland cover crops = Annual Cereal Rye used widely (workhorse of cover crops). The long-lasting residue helps suppress summer weeds (maybe an allelopathic effect in the soil)? Wild rye has similar effect? Cereal Rye/residue will stop pesticide resistant mares tale (conyza canadensis, horseweed) from germinating. In a heavy mat of cereal rye, soybeans will come up nicely along with red root pigweed, but the mares tail stops where the rye cover starts.
I’ve had issues planting natives into established cereal rye. It definitely suppresses the natives. Best to spray glyphosate and either lightly till or burn off before seeding natives.
Hi Chris-someone forwarded your blog to me. Nice. Many places do use Canada wild rye as a native cool season species with built in obsolescence. It goes gangbusters in the first 3-4 years but then tends to start declining. That decline can be “encouraged” with a spring burn that will weaken the wild rye. In a research project involving various seed mixes, planting seasons and planting equipment, (on 3 stations in MN and one in IA) we learned that Canada wild rye is indeed correlated with Canada thistle suppression. This effect was not as strong after a spring burn later on. In my mind, the trick is to plant a good representation of cool season natives including longer lived species like June grass and forbs that fill the spaces that would be otherwise occupied by germinating exotics. Dormant broadcast seeding worked best in this study for establishment of diversity and native cover (and less exotics). We also learned that Canada thistle probably doesn’t have any special tricks like allelopathy, but simply occupies the same space as germinating prairie forbs would. It looks like native “weedy” species (annuals and biennials) are important in suppressing exotics as well, likely due to allelopathy. But I agree completely that site characteristics, climate and weather patterns all matter and can be game changers.
Diane Larson, USGS, was the PI. There is a fact sheet on her website here that summarizes results of this study to date. http://pubs.usgs.gov/fs/2013/3049/ This year was a 10 year monitoring event so stay tuned…
In response to Stan Stankewich’s question about later interseeding into Canada wild rye, I think this idea is right on. Good timing for interseeding is probably when the CWR starts to decline creating openings (read opportunities!) for new plants…might as well be your interseeded plants, to establish and thrive. We’ve even interseeded into dense warm season grass after a summer burn with nice establishment of diversity. It took time for it to all show up, however.
It is always a pleasure to see a response from someone who is of the caliper of the Royal Society of Scientists, but from our own country. It is also excellent to suggest that a lengthy factorial study be undertaken and then have it immediately given to you. After reading Diane Larson’s paper, I think the question that remains is whether control efforts during establishment will give competitors the opportunity they need to fill the spaces and reduce the cover of Cirsium arvense in the future. With most invasive species the declines with control efforts are obvious. However, in the case of Cirsium arvense I am not convinced mechanical or chemical control is effective over the long term. In some cases I think the efforts that are put toward controlling invasive species actually exacerbates the problem by continuing the conditions the invasive species need to survive.
When you say ultra high rates for the initial spike, what numbers were being used/discussed?
Nate, good question. I don’t remember exactly numbers and I think it varies by restoration (in practice, if not in the research project itself). Probably ten times or more what they would use for that species normally. Maybe someone more familiar with the work can chip in with better numbers.
We have some sites that are heavy to Canada wild rye after 3-4 growing season, with warm season grasses at 10-15% cover. We are reluctant to prescribe a burn, on the chance that we will knock our cool seasons back too far and end up with an explosion of Canada thistle. For the sites where you observed a transition from near mono-culture to nice prairie, did you use a burn to help it along?
Carol, we burn as frequently as we can during the first several years of establishment – including in those wild rye monocultures. However, we don’t fight Canada thistle in a major way either, so I can’t tell you how that might affect that species. Based on experience, though, I think an early spring burn would not have a negative impact on wild rye, but might decrease thatch amounts enough to stimulate your other desired species.
It is easier to use a hoe in spring to chop off the new field thistle rosettes when the ground is cleared by mowing or fire. This sets the thistles back enough that other plants get an advantage in the race for light. The thistles that grow tall then can be hand pulled. This is a lot of work but over a few seasons the thistles get exhausted and the amount of work continually diminishes. It is also a good idea to make sure there are not invasive weeds nearby that can spread seed into an area you are trying to restore. An ounce of prevention is worth a pound of cure.