weeds | The Prairie Ecologist

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.

Black-eyed susans (Rudbeckia hirta) in restored prairie - TNC Platte River Prairies, Nebraska.

Black-eyed Susan is a species that has shown some promise as a species that can compete against invasives but still allow the establishment of a diverse plant community around it. The Nature Conservancy’s Platte River Prairies, Nebraska.

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.

This 2004 shows one of our Platte River prairie plantings in its third year of growth. Canada wildrye is visually dominant, but other species are present as well.

This 2004 photo shows one of our Platte River prairie plantings in its third year of growth. Canada wild rye is visually dominant, but other species are present beneath its canopy. Many of our young plantings from about that time period looked much like this for several years in a row.

After this prairie was seeded in 2000, it was a near monoculture of Canada wild rye for several years but today is our showiest wildflower patch.

After this prairie was seeded in 2000, it was a near monoculture of Canada wild rye for several years. Today it is among our most diverse prairies and showcases our showiest wildflower patches. (July 2015 photo)

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.

Grassland Restoration Network Meeting. Hosted by TNC Minnesota.

There is great value in getting a bunch of restoration practitioners together in one place. We often bring home new ideas to try. Sometimes they even work. 2015 Grassland Restoration Network workshop – Minnesota.

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.

When I was at the Niobrara Valley Preserve a couple weeks ago, I spent some time exploring the area north of the river where the 2012 wildfire ripped through oak savanna and ponderosa pine woodland. As discussed in earlier posts, the density of trees, especially eastern redcedar, fueled a fire that killed nearly every pine and cedar in the 3000 acres of Preserve land on the north side of the river. Most oaks and other decidous trees were topkilled, but many resprouted within a few weeks of the fire. I have been following the regrowth and recovery of this part of the Preserve with great interest, and trying to help the Preserve staff as they think about how to manage the area in the future.

Here is a series of photos from an uphill hike I took on September 18. The photos are roughly in order of elevation, starting at the river road (just above the floodplain) and proceeding upslope to the ridgetop at the north edge of the valley.

On the first slopes above the river road, hemp (Cannabis) and marestail (Conyza) dominate the understory of a woodland that now consists mainly of skeletons of eastern redcedar and oak trees. Most of the oaks have resprouts from their bases, however, and a few still have live branches up high.

The abundance of marestail (a native pioneering species) is especially interesting to me because it’s the same species that usually dominates two-year-old prairie plantings. This is the role it plays in ecosystems, and it plays it well. It’s difficult to see very much below the marestail, but when I looked closely, I found scattered grasses, sedges, and wildflowers – a good sign of future recovery.

As I walked higher and got into the prairie-covered slopes, ragweed (Ambrosia) replaced marestail as the visually dominant plant in the formerly shaded areas beneath cedar trees. The ragweed is playing the same role as the marestail – quickly filling in the open space until a more permanent plant community establishes. That community should move in pretty quickly in cases like that shown in this photo, in which a cedar tree is surrounded by prairie.

Higher up the slope, large areas of prairie had not been encroached upon by cedars, and recovery after the fire was just as predicted – quick and easy. The vegetation was still a little thin, but that was more of an aftereffect of the 2012 drought than of the fire. In this image you can see the scattered cedars further downslope (such as the one featured in the previous photo).

Almost every bur oak tree I saw was vigorously resprouting from the base. Those numerous stems should thin themselves down to three or four major trunks over the next decade or so. Some of the branches were already 6-8 feet high, so recovery is proceeding quickly. These oaks were growing along the edge of one of many steep draws scattered along the north side of the river. As I was wading through 3-4 foot tall marestail, I couldn’t help but wonder if that dense growth and the presence of mountain lions in the area explained the near absence of deer browsing on the oak sprouts (Ecology of Fear). I don’t know if the deer felt it, but I sure had moments of discomfort, knowing that if a lion was hiding in the weeds nearby, the steep slopes and thick vegetation would make escape nearly impossible. It made my hike a little more exciting, but I didn’t stay down in those draws very long…

I was surprised and pleased to see numerous examples of large sedge patches growing under the marestail forest, especially on the steeper portions of draws. I don’t remember seeing many sedges last year, so either I missed them or they are expanding rapidly. Either way, they will sure help stabilize those slopes as other plants move in to join them, and they’ll also help carry fire when we restart fire management of the area.

High on the slopes, where ponderosa pine and eastern redcedar had dominated just a few years ago, the scenery was every bit as spectacular as it had been before the fire – just different. Marestail was abundant here too, but there was quite a bit of grass and wildflower cover as well, and several shrub species were flourishing, including smooth and skunkbush sumac, chokecherry, snowberry and others. Despite the density of scorched tree trunks, the overall feel of the slopes was not one of death and destruction, but rather of abundant life.

Even the very steep erodible slopes at the very edge of the ridge top were full of previously established perennial wildflowers and shrubs, as well as colonizing annuals.

I came down the slope after my walk with a great feeling of optimism. My greatest worries about this area of the preserve had been that

1) Invasive plants would fill the slopes before the native vegetation could recover, and we’d be faced with the difficult challenge of attacking those invasives in difficult terrain.

2) Numerous eastern redcedar trees would colonize the slopes before there was enough vegetation to carry prescribed fires to knock those cedars back.

3) Soil erosion would be so severe that the seed bank needed to reestablish the native plant community would wash down the slope, along with the topsoil those plants needed to grow.

None of those three have occurred – or at least to the extent I feared they might. There has been some erosion, but much less than I anticipated, and it doesn’t seem to be affecting vegetation recovery much. I haven’t seen any truly invasive plants yet – which doesn’t mean they aren’t there, but they sure aren’t roaring in. Finally, the recovery of the vegetation has been fast enough that we should be able to start running prescribed fires up the slopes within the next few years. I didn’t see any little cedar trees on my walk, and while I’m sure there are a few around, the abundance is much less than I feared, and our ability to use prescribed fire should make it fairly easy to control them, except on the steepest slopes.

Most of all, the beauty of the Niobrara Valley has survived the wildfire. The pines are gone from some parts of the valley, but are still doing well in other areas nearby, including other parts of the Niobrara Valley Preserve. Whether or not (or when) they’ll return to the site of the 2012 fire is still an open question. Regardless, there is abundant life on the slopes north of the river. Just because those slopes will be dominated by different species than before doesn’t change the scenic or ecological value of the site. It’s still one of my favorite places on earth.

The Prairie Ecologist

Essays, photos, and discussion about prairie ecology, restoration, and management

Tag Archives: weeds

Chuck Norris of the Prairie

Continuing Wildfire Recovery at the Niobrara Valley Preserve