Now You See Them, Now You Don’t (But They Might Still Be There!)

Grazing, especially by goats and/or sheep, is often promoted as a control method for weeds or shrubs.  Depending upon the life strategy of the weeds being targeted, grazing can be effective, but it’s important to set realistic objectives.  As you might expect, many perennial grasses, forbs, and shrubs have evolved strategies for surviving repeated defoliation.  In those cases, grazing may appear to effectively control plants while grazers are present, but the plants bounce back right after grazers are removed.

One of my all-time favorite research projects showcases this exact phenomenon at a site in South Dakota owned by The Nature Conservancy.  Back in the early 1990’s, an estimated 75% of the Conservancy’s Altamont Prairie Preserve was covered by leafy spurge (Euphorbia esula).  In 1994, goats and sheep were installed in separate pastures and spurge was treated by using periodic high-intensity grazing sessions during both early summer and early fall.  Both the goats and sheep were very effective at eating the spurge plants, and after five years, managers conducting walk-through inspections the site felt like excellent long-term control of spurge had been achieved.  Inside small exclosures, spurge was still abundant and vigorous, but outside the exclosures, almost no plants could be seen.  As a result, the goats and sheep were removed and everyone was happy.

One of the goats used at Altamont Prairie and an exclosure showing a dramatic difference between abundant and blooming leafy spurge in ungrazed areas and no apparent spurge in grazed areas. Photos courtesy of TNC’s Minnesota, North Dakota and South Dakota Chapter.

…Until the next season when spurge plants popped right back out of the ground and the pasture looked essentially as it had before the grazing treatment had started.  In dismay, the managers looked for another option and decided upon flea beetles (Apthona spp.), which ended up being a much more successful choice, greatly reducing the footprint of leafy spurge over the next several years.

You’d be excused for thinking the use of sheep and goats was a total waste of effort, but additional data collected at Altamont Prairie adds some interesting nuance.  As it happens, mean Floristic Quality (a kind of qualified plant diversity metric) stayed relatively stable within the grazed area during the five years sheep and goats were present.  During the same time period, mean Floristic Quality decreased significantly in exclosures.  In other words, while grazing didn’t eliminate the spurge problem, it may have stabilized some of its negative impacts for a while.

This, to me, is one of the best attributes of many grazing-for-weed-control efforts.  Even if grazing can’t eradicate many weeds/shrubs from a prairie, it might be a strategy that prevents further spread (eliminating flowers and reducing vigor for belowground reproduction) and/or reduces the weed’s ability to compete with desirable plants.  In a large site where more effective long-term strategies (such as selective herbicide application or biocontrol releases) aren’t feasible across the whole area, using grazing as a suppression tactic in some areas of the site while you kill it in others can make a lot of sense.  In other words, grazing might buy you time to work on a problem that would otherwise seem overwhelming in scope.  (However, it’s also important to remember that grazers will also be eating and suppressing the vigor and reproduction of desirable species with similar growth strategies to the invader you’re targeting.  If you do succeed in reducing populations of invaders, you might also reduce populations of those desirable plants.)

Grazing can sometimes provide effective control of short-lived plants if it prevents flowering and seed production and forces plants to die without reproducing.  Just remember that more seeds are likely waiting in the soil, so it will likely take repeated grazing treatments to reach your goal.  Here in Nebraska, we often use short-term intensive grazing as a tool to knock back the competitive ability of perennial cool-season grasses such as smooth brome (Bromus inermis) or Kentucky bluegrass (Poa pratensis).  We don’t expect the grazing to kill those grass plants (and it doesn’t) but we can allow other plants a chance to flourish for a few years until the invasive grasses regain their vigor.  By repeating the treatment periodically, we can maintain a more diverse plant community.

Periodic early-season cattle intensive grazing helps us temporarily suppress cool-season invasive grasses like smooth brome and reduce its ability to outcompete many native grasses and wildflowers.

Personally, I’ve never used goats or sheep to help with a management challenge.  In contrast with cattle, goats and sheep, feed preferentially on forbs, and I’m usually trying to suppress grasses and encourage forb growth.  However, I do think goats, sheep, and cattle can all play important roles in controlling invasives as long as you don’t expect them to do more than they can.  I worry that landowners and land managers can sometimes end up paying an exorbitant price to someone that brings animals in with the promise of weed control.  It’s important to remember that if you do that, you’re providing food for that contractor’s animals, and that should be factored into whatever price one of you pays the other.  When we use cattle for prairie management, the cattle owner always pays us.  That seems not to be the case with many goat grazing operations.  I’m not saying it’s wrong to pay someone to graze their goats on your land, I’m just saying it’s important to fully process what each party is getting from the transaction.  That includes the forage provided to the animals from your land, the time and expenses incurred by the owner of the animals, and  – importantly – the actual effectiveness of the treatment.

As long as you have clear objectives and a good understanding of the plant(s) you’re targeting, grazing may be a great tool for invasive species control.  Just remember one of the biggest lessons from the South Dakota spurge experiment: just because you can’t see the invasive plant anymore doesn’t mean it’s gone!

Hubbard Fellowship Blog – Stewardship Positivity

The following post was written by Evan Barrientos, of our two Hubbard Fellows for this year.  Evan is a talented writer and photographer, and while you’ll get the chance to see some of his work here during the next year, I also encourage you to check out his personal blog.

Although I’ve been participating in land management since high school, I still find myself learning so much from it, although perhaps not in the way you’d expect. Yes, I’ve learned several management techniques and strategies since starting the fellowship, but the lessons I consider most valuable are the ones that teach me how to think about land stewardship. Let me explain.

If you were a Hubbard Fellow during the second week of June, you would probably find yourself riding an ATV back and forward across one of our restored prairies, searching for the fluffy purple flowers of Musk Thistle. Upon spotting a thistle, you would pluck off all the flowers, thrust your spade through the base of the thistle with a satisfying crunch, pull out the plant, and then knock the dirt off of any uprooted roots. Over the next three weeks you would repeat this process thousands of times until you had covered every inch of all 14 of our Platte River properties and their 4,000+ acres. Then you would check them all again.

We celebrated the end of thistle season by burning the flowerheads in a bonfire.
When we finally finished musk thistles we celebrated by burning the seed heads that we had collected in a bonfire.

This may sound like exhausting and repetitive work, and it can be, but that wasn’t the hard part for me. The hard part was staying positive when it felt like I wasn’t doing enough. I felt this way when I returned to a prairie for its second thistle check and found piles of thistle seed below “zombie thistles” (thistles that flowered and produced seed after I chopped them because I left too much dirt on the roots). Or when I walked through a prairie that I had already checked twice and still found thistle stalks that had already released their seed to the prairie. Most of all, deciding to spend July 2nd chopping thistles before they released more seed instead of spending time with my family forced me to think hard about my role as a land steward.

As a land steward you develop a strong connection to the land you are working on. Seeing a healthy community of native species flourish on your property is extremely gratifying, but it also pains you to see invasive species spreading. Land stewards almost always have more tasks than they can complete and it’s very easy to let this make them feel overwhelmed and stressed, but it doesn’t have to be this way. After reflecting upon the first month of my fellowship, here are three lessons I’ve learned so far about being a happy steward:

  1. I cannot control nature. I am a steward, not a god. Expecting myself to control exactly which species grow on a property will only bring me frustration. The role of a land steward is not to dominate the forces of nature, but to regulate its extremes. Translation: my job isn’t to exterminate musk thistles, but to prevent them from outcompeting other species and lowering overall biodiversity.
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A Regal Fritilary (Speyeria idalia) on Musk Thistle (Carduus nutans). Like it or not, Musk Thistles have become part of the local ecosystem. Being a steward doesn’t mean exterminating thistles, but keeping them under control.
  1. There is no endpoint. A land steward’s work is never “done.” My job isn’t to “fix” a property; it’s to guide the property toward a range of conditions that meet our management goals. Removing thistles from the same property year after year does not mean that we are failing at our job of “restoring” the prairie. On the contrary, it means we are doing our job of actively fostering biodiversity.
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Common Mullein (Verbascum thapsus) is non-native, but also non-invasive. We don’t remove it because it doesn’t lower plant diversity.
  1. Stewardship should be viewed as a positive action, not negative. There are two very different ways to look at land management. From one angle, a day spent chopping thistles could be considered a violent battle against an evil enemy; a task to evict an unworthy invader. From another angle, it could be considered a process of creating beautiful and biodiverse prairies. In my experience, viewing invasives as enemies just leads to exhaustion and bitterness. Only by viewing stewardship as a process of care and creation, in my opinion, can one generate the tremendous amount of energy needed to take on its many tasks.
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Black-eyed Susans (Rudbeckia hirta) in the Platte River Prairies, Nebraska.

Land stewardship is an essential component of conservation and it’s imperative that we do it well. Unfortunately, it also is a very demanding job that can burn you out if you’re not careful. I’m happy to say that the first month of this fellowship taught me some very important lessons about setting realistic expectations and viewing my work as a positive contribution to prairie biodiversity. It’s important to be a happy steward!

Categorizing Invasive Plants

Managing invasive plant species is often the greatest challenge faced by land managers.  Because there are so many invasives and so little time, it’s critically important to be thoughtful about how to approach them.  There is much good advice available about how to prioritize which species to focus on and how to approach those priority species.  My own approach to invasives continues to change over time.  For what it’s worth, here’s how I think (today) about categorizing invasive plants on our sites here in Nebraska.

I can put most invasive plant species into one of four categories that describe how we approach control.

  1. Thin the matrix
  2. Beat them back
  3. Nip them in the bud
  4. Live with them

 

Category 1 – Thin the matrix.

Invasive grasses, such as Kentucky bluegrass, smooth brome, and tall fescue are excellent examples of species in this group.  They are plant species that are common enough that they occur throughout most of our sites, and – if left unmanaged – can form thick monocultures that exclude most other plant species.  Eradication of these species is not possible without losing many of the other plants we are hoping to conserve.  Instead, our general approach is to reduce their dominance and limit their impact on the diversity of the plant community.  (I wrote about this approach in an earlier post, using Kentucky bluegrass as an example.)

Essentially, we try to use fire, grazing, and/or mowing to weaken invasive grass plants and open up space between them for other species to flourish.  Because these suppression strategies also have negative impacts on some native species, we are careful not to use them too many years in a row.  Instead, we apply them periodically, whenever it looks like the invasives are starting to exert their dominance a little too much.

Prescribed fire and grazing are the two best ways we attack invasive grasses such as smooth brome and Kentucky bluegrass.
Prescribed fire and grazing are the two best ways we attack invasive grasses such as smooth brome and Kentucky bluegrass.

Category 2. Beat them back.

This group includes perennial plants that radiate outward other otherwise spread from an established source population.  Species we commonly deal with that fit into this category include purple loosestrife, sericea lespedeza, and Canada thistle.  It can be tempting to jump in and start attacking (with herbicides or other approaches) the biggest thickest patches of these, but that’s rarely the smartest strategy.  Instead it usually makes more sense to work from the outside edges of an infestation toward the middle – or source – so that the problem doesn’t continue to get worse as you attack.  I wrote an earlier post on that topic as well…

An exception to the “work from the outside edge first” rule applies to species such as Siberian elms that may be spreading from a single discrete patch of parent trees.  If it’s possible to eliminate that source population by cutting down a handful of trees, it absolutely makes sense to do that first.  Next, it’s smart to target other elms that are big enough to produce seed before working on the smaller ones – rather than blindly following the rule about working from the edges of an infestation.  Rules are meant to be broken, after all.

 

Category 3. Nip them in the bud.

This category contains invasive species that are just starting to show up in our area or at a particular site.  Here, the tactic is to seek and destroy new plants as soon as they arrive, to prevent the species from becoming established.  After all, it’s always better to attack an invasive species before it gains a foothold.

Many species can fit within this group.  For us, Common reed (Phragmites australis), crown vetch, garlic mustard, and Queen Anne’s Lace (aka wild carrot) are good examples.  Sometimes, we’re not sure if a species will really cause serious problems if it becomes established at our sites (e.g., Queen Anne’s Lace) but if minimal effort can prevent that establishment, it seems  like time well spent.

Our approach to musk thistle sort of fits into this “nip it in the bud” category, but for other reasons.  Musk thistle is an officially-designated noxious weed in Nebraska, and all landowners (including us) are required to eradicate it from their property each year.  If it weren’t for the state law, musk thistle would not be among our highest priority species because it really doesn’t cause big problems in most cases (on our sites).  It is most abundant where the dominant vegetation has been recently weakened by fire, grazing, or drought, but quickly diminishes in abundance when grasses recover their dominance.  However, to abide by the law and to prevent thistles on our land from going to seed and affecting our neighbors, we do our best each year to eradicate musk thistle.

 

Tier 4. Live with them.

This last group includes species we don’t actually consider to be invasives, at least by the criteria that a truly invasive plant acts to reduce biological diversity or otherwise simplify (and thus weaken) natural communities.  Many native species are considered weeds by some of our neighbors, but we like having them around.  Prime examples include annual sunflower and ragweed species.  However, many non-native plants fall within this category as well, including common mullein, dandelions, goatsbeard, marestail, and sweet clover.  Sometimes, we spend some time collecting and/or analyzing data to help ensure that we’re categorizing these species correctly.  A good example of that was discussed in an earlier post on sweet clover.

Dandelions are a species we just live with.  They're great for early season pollinators, and aren't aggressive - they just fill space when the perennial plant community is weakened (as they are doing here in the lot around our shop buildings).
Dandelions are a species we just live with. They’re great for early season pollinators, and aren’t aggressive – they just fill space when the perennial plant community is weakened (as they are doing here in the lot around our shop buildings).

Switching Categories.

Ideally, of course, we’d be able to move some invasive plant species from one category to another, so that populations of “matrix” invasives shrink to the point they are in discrete patches and we can “beat them back.”  Likewise, it’d be great if “beat them back” invasives became rare enough that we could eventually “nip them in the bud”.  Unfortunately, reality usually goes the other direction.  For example, we’re dangerously close to having to shift garlic mustard from “nip it in the bud” into the “beat them back” category (if not the “thin the matrix” category!) at a nice woodland site we manage.  We’ll see what the next year or two brings.

We hope that using more frequent fire (along with other methods) will help us prevent garlic mustard from spreading across our whole property at the Rulo Bluffs Preserve, but it's a big challenge.
We hope that using more frequent fire (along with other methods) will help us prevent garlic mustard from spreading across our whole property at the Rulo Bluffs Preserve, but it’s a big challenge.

Regardless, I find it helpful to think about our invasive plants within categories like these because we can more easily define both our control strategies and objectives.  Putting a species into the “nip it in the bud” category helps make it a top priority and we can prioritize resources toward keeping it rare.  Just as importantly, if we know that we’re only trying to suppress the dominance of smooth brome, not eradicate it, we don’t have to beat our heads against the wall in frustration because smooth brome is still present.

We spend more time on invasive plant control than on any other land management activity.  Unfortunately, that’s true of most land managers I know.  More unfortunately, invasive species numbers are going up, not down.  It’s not time to throw in the towel just yet, but it is absolutely critical to be organized and thoughtful about how we approach these invaders.

Hopefully, being organized will allow us to spend less time on invasives and more time enjoying the sites we manage!

Flying Carp (WATCH OUT!!) on the Missouri River

Last week, I attended the Nebraska Natural Legacy Project’s annual conference, which was terrific.  At the end of the conference, I had the chance to go on a boat tour of the Missouri River south of Nebraska City.  The tour was led by Gerald Mestl (Nebraska Game and Parks Commission) who did a great job of explaining both the history and current status of the river.  We also got to see examples of side channel and bank restoration efforts and hear about ongoing research and monitoring efforts on fish and other Missouri River species.

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I’d love to give you a full recap of the information Gerald gave us on the tour, but I honestly don’t remember much of it.  Unfortunately for Gerald, but to the great entertainment of those of us on the tour, our attention much of the boat trip was diverted by numerous flying carp.  Yes, you read that correctly.

Asian carp, particularly silver carp, have invaded the stretch of the Missouri we were touring.  Silver carp are an invasive fish species that quickly become the dominant fish species in a lake or river (by biomass), though it’s not always clear what or how much negative impact they have on the ecosystem they invade.  Because silver carp are plankton feeders, they probably compete most with other species utilizing that same food source, including many larval fishes, paddlefish, and freshwater mussels.  Gerald said that so far they’ve not seen any obvious impacts from the Asian carp invasion of the Missouri, with the possible exception that paddlefish weights seem to be less than they used to be.  Of course, that doesn’t mean other impacts won’t arise as time goes by and more research is conducted.  Unfortunately, once Asian carp become established, there doesn’t seem to be a way to remove them from an ecosystem.

While there are concerns about what the impact of silver carp (and other Asian carp, including bighead and grass carp) will be on the Missouri River ecosystem, those of us on the boat tour last week were mostly concerned about ducking them as they came flying past or into our boats.  It turns out that silver carp have a propensity to jump (up to 10 feet!) out of the water in response to the vibrations caused by boat motors.  This wasn’t much of an issue in the main channel of the river, but as soon as we entered any side channel or backwater area where the water wasn’t strongly flowing, silver carp started flying out of the water like big slimy popcorn (or something).  Thus, my recollection of the tour and the information poor Gerald was trying to impart to us goes something like this:

“Historically, the banks of the Missouri River often consisted of steep banks that were being actively eroded by the flowing channel.  Some estimates are that those banks could shift an average of 180 feet a year!  That’s really important to understand because LOOK OUT!!

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“Ok, anyway…  Another important thing about the historic river is that it was full of snags (dead trees).  Navigation was really tricky because of all the big cottonwood skeletons along the bank and shallow islands.  Today, we don’t see much of that kind of habitat, which was probably really importWATCH YOUR HEAD!!

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“Yeah, so there are a number of fish species that aren’t doing well in the Missouri or lots of other similar rivers that have been severely altered.  Benthic (bottom-feeding) fish, in particular, are having a hard time, including species such asWHOA!! DID YOU SEE THAT??

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“We’ve been doing quite a bit of research on some of these rare fish and learning a lot.  For example, it appears possible that pallid sturgeon (a federally-listed species) might actually be periodically moving from the Missouri into the lower Platte River for certain reasons.  If that turns out to be true we might have to re-evaluaWOW! LOOK AT THE SIZE OF THAT ONE!!

Nelson Winkel (The Nature Conservancy) holds a siver carp that jumped into the boat while RaeAnn Powers looks on.
Nelson Winkel (The Nature Conservancy) holds one of the smaller silver carp that jumped into our boat while RaeAnn Powers looks on.

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“Here at Hamburg Bend, there was a big restoration project that included the creation of a side channel that now forms a shortcut through a big bend of the river channel.  That side channel provides important habitat for a number of species, includOH MAN!  DID THAT ONE HIT YOU IN THE HEAD??

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“Ok, where were we… oh yeah, so the current main channel of the Missouri River has been constrained to a 600 foot width.  That’s much less wide than the historic channel, and of course because it no longer is allowed to move around the floodplain, we don’t see the kind of bank erosion and associated habitat that used to be so important for thiWOOHOO!! DID YOU SEE HOW HIGH THAT ONE JUMPED??

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“On another subject, there has been some interesting recent research on turtles and their use of the Missouri River.  Among other things, they’re seeing some surprisingly long-range movement of turtles – including one that traveled 50 miles upstream!  That’s really interesting, and makes you think abouHEY! HEADS UP!!

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“You know, one of the main challenges of the Missouri River is the balance between recreational, flood control, and navigational needs (among others).  Trying to figure out how to restore and manage flows and habitats is complicated by LOOK – TWO MORE!!

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“Oh never mind… let’s just watch carp for a while.  At least that way we canI THINK THAT ONE JUMPED OVER THE WHOLE BOAT!!

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“So, that’s our tour for the day.  Thanks for coming out, and I hope you enjoyed it.  Sorry about all the fish slime on your shirt.  I hope that bruise on the side of your face heals ok…”

Blowing Against the Wind?

As I mentioned last week, I recently spent a couple days helping our land manager, Nelson Winkel, pull garlic mustard at our Rulo Bluffs Preserve in southeast Nebraska.  The invasive species has just started to invade our property within the last several years.  We’ve heard stories from colleagues in other places about beautiful woodland plant communities turning into monocultures of garlic mustard within a relatively short time period.  We’d sure like to keep that from happening at our Preserve.

So, we pulled garlic mustard plants.  A lot of them.  On the first day, I figured we pulled at least 25,000 plants.  That’s a very conservative estimate.  The second day was longer, but we did more searching and less pulling.  This wasn’t the first trip to pull either, so we were just trying to get what was leftover from the previous efforts.

Nelson Winkel, showing off one patch's worth of pulled garlic mustard plants.  The Nature Conservancy's Rulo Bluffs Preserve - Nebraska.
Nelson Winkel, showing off one patch’s worth of pulled garlic mustard plants. The Nature Conservancy’s Rulo Bluffs Preserve – Nebraska.

The Rulo Bluffs Preserve is 444 acres.  Hand-pulling weeds doesn’t seem like a very sustainable strategy for invasive species control at that scale.  In fact, it’s downright depressing because we pull more plants from more locations every year.  We’re clearly not winning.  So why bother?

It’s a good question, with several answers.  The first answer is that we’ve got some ideas for increasing our effectiveness.  Nelson and I talked as we worked about how we might put together a small army of volunteers to come help us pull each spring.  The big challenges are that the site is far from population centers (more than two hours from Lincoln and Omaha), has difficult terrain to hike in, and garlic mustard doesn’t bloom at exactly the same time each year, so we’d have to schedule work days on fairly short notice.  On the other hand, I think there are people who’d be glad to help, and it is a beautiful place to work in the spring time – lots of warblers and other birds above, and plenty of woodland wildflowers below.

In addition to finding more people to help hand pull, we hope to decrease the number of plants we need to pull in the bigger, more established, patches by doing some herbicide work in the late winter.  Garlic mustard is a winter annual or biennial which germinates in one season, overwinters as a rosette (a few leaves, low to the ground), and then flowers in the late spring of the next year.  Our colleagues in more eastern states have been dealing with garlic mustard longer than we have, and have had luck spraying the rosettes with Glyphosate herbicide on warm February days.  Spraying in the winter works well because there are very few other woodland plants that are green (and thus susceptible to Glyphosate) in February.  They don’t usually spray in the early winter because many rosettes die on their own over the winter, and by waiting until February, they can focus only on those most likely to bloom in the coming year.  Nelson was marking the bigger patches we found with a GPS unit so he can find them next winter and try the spraying technique.

Small patches of garlic mustard such as this one might eventually be eliminated by hand-pulling.
Small patches of garlic mustard such as this one might eventually be eliminated by hand-pulling – especially if we find and treat them every year.  Larger patches are much more problematic.

The second reason we’re still trying to suppress garlic mustard is that I hope we can buy some time until better control options become available.  There has been some work to develop a biocontrol technique (using insects from the native range of garlic mustard), for example, and if something like that turns out to be effective, I want to be sure we still have some woodland left to save.  Unfortunately, I’m hearing that biocontrol development has stalled at the moment.  Apparently, in at least some places, people are seeing garlic mustard populations decline steeply on their own – as if the plants are outcompeting themselves and self-thinning.  That could be great news, but only if the native plant community rebounds as the garlic mustard declines, and I haven’t been able to find anyone who can tell me whether or not that’s the case.  I sure hope it is, but I’d feel better if the biocontrol folks kept forging ahead on the development of that control option anyway.  Regardless, I’m holding out hope that either garlic mustard will turn out to be a temporary nuisance (seems unlikely?) or that biocontrol or better control options will be developed in the next several years.  I could be naive, but at least it gives us something positive to think about while we’re pulling up thousands of garlic mustard plants…

While we look for better control options, we’re also trying to change the playing field for plant competition at Rulo Bluffs and give garlic mustard less of an advantage.  With considerable help from Kent Pfeiffer of Northern Prairies Land Trust, and funding from the Nebraska Game and Parks Commission and others, we’ve been trying to ramp up our stewardship work during the last several years.  We’ve not done as much burning as we’d like to, but are earnestly trying to change that.  Last fall, a contractor did some “hack-and-squirt” herbicide treatment to kill many of the smaller understory trees that are shading out the herbaceous plants on the ground.  We’ve also been doing mechanical shredding of brush on ridgetops to help the grassland, savanna, and open woodland plants there.  All of this work is aimed at getting more light to the ground, which should stimulate increased oak regneration and a stronger, more diverse, herbaceous community on the woodland floor.  In addition, we hope that increased light will put shade-loving garlic mustard at a disadvantage, at least in some parts of the woodland.  From talking with others around the country, they’ve seen mixed results from similar work.  I guess since we want that light on the ground anyway, we’re going to forge ahead – and hope we don’t make things worse.

Jack-in-the-pulpit is one of many woodland flower species that help make the Rulo Bluffs Preserve unique and valuable.
Jack-in-the-pulpit is one of many woodland flower species that help make the Rulo Bluffs Preserve unique and valuable.

Finally, we’re pulling garlic mustard because the Rulo Bluffs Preserve is worth the effort.  It’s one of the few remaining high-quality oak woodlands in Nebraska, and hosts a wide diversity of plant and animal species – many living at the edge of their geographic range.  In addition to lots of mayapples, jack-in-the-pulpit plants, and woodland phlox, we also found two orchid species blooming last week – the showy orchid and the yellow lady’s slipper orchid.  We walked around beneath eastern deciduous tree species such as chinkapin oak, black oak, and Ohio buckeye.  Several animal species at the preserve, including zebra swallowtails, timber rattlesnakes, and southern flying squirrels, are only found on the very eastern edge of Nebraska.  While some of those species are common to the east of us, it is probably important to protect their genetic diversity by maintaining populations across their entire range.  That should allow the species to better adapt and survive in changing conditions over time.

Genetic and biological diversity aside, the Rulo Bluffs Preserve is also important because it’s a beautiful place.  We need to keep some aesthetically-pleasing natural areas around for people to enjoy.  Despite our aching backs, Nelson and I had a great time exploring the preserve last week, marveling at warblers, flowers, velvet mites, and other wonders.  It’s possible that we’ll invest a tremendous amount of time and money into stewardship and restoration at the Rulo Bluffs Preserve over the next several years and still lose out to garlic mustard.  There are plenty of examples of that happening elsewhere.  I guess we’re not ready to concede the battle, however – there’s too much at stake.

Killing Small Trees in Prairies – A Helpful Tool

One of the greatest challenges of prairie management, especially in small eastern prairies, is managing the invasion of small deciduous trees.  Most prairie species (plant and animal alike) thrive best in open treeless habitats.  Encroaching trees can fragment large prairies into smaller pieces, shade out many species of prairie plants, and harbor both predators and invasive species that can change the whole balance of power in a prairie community.

Siberian elms are fast becoming a major threat to many prairies.  Killing numerous small trees like these without impacting the diverse prairie community around them can be difficult.
Siberian elms are fast becoming a major threat to many prairies. Killing numerous small trees like these without impacting the diverse prairie community around them can be difficult.

So what to do?  Controlling species such as eastern redcedar is relatively easy – they can simply be cut down, or even more quickly wiped out with a well-timed and planned prescribed fire.  Unfortunately, most deciduous trees resprout after being cut or burned, so killing them usually requires the use of herbicide to prevent that regrowth.  Cutting trees down and painting their stumps with a small amount of herbicide is a simple and clean way to eliminate them, but that task becomes much more daunting when there are hundreds (or more!) of small trees to deal with.

Over time, we’ve been using and refining a simple tool that makes the task much more manageable.  Some herbicides for controlling woody plants can be applied through a technique called “streamlining” or “basal bark treatment”, in which the herbicide is mixed with oil and applied to the outside of a young tree without first cutting it down.  It’s a nice alternative method, but after using it for several years, we had to keep replacing sprayers because the oil (and maybe the herbicide) was pretty hard on gaskets and other rubber/plastic components.

Then our former land steward, Chris Rundstrom, came up with the idea of adapting a tool developed by Jack McGowan-Stinski in Michigan called a PVC herbicide wand.  The wand has a sponge at the end, and was developed to apply herbicide to cut stumps cleanly and easily.  Chris thought it might also work well for the basal bark treatment – and he was right.

The "killstick" can make the difficult task of suppressing invasive trees much more manageable.
The “killstick” can make the difficult task of suppressing invasive trees much more manageable.

Over time, Chris modified the design of the “killstick”, as it became known to us, to make it work better for its new purpose.  Recently, our technician-turned-fulltime-land manager, Nelson Winkel, has been further refining it.  Now, we’ve got it working pretty smoothly and have decided to share what we’ve learned with everyone else struggling to fight off invading small trees.

Below are two links to instructions that will show you how to build and use the killstick yourself.  We’ve had good luck using it against every species of deciduous tree we’ve tried it on, as long as the trees are smaller than about 3″ or so in diameter and have smooth bark.  The brand of herbicide probably isn’t very important, as long as it contains the chemical Triclopyr and is labeled for the basal bark or streamlining technique.  Be sure to follow the label directions for the mixing and handling of the chemical.  The killstick allows you to apply the herbicide mixture to the tree through a wick rather than with a sprayer, but all other label directions should still apply.

Detailed Instructions

A Printable Tri-Fold Guide

If you try it out, we’d love to hear your opinions and ideas for further refinement.  You can leave a comment below or contact Nelson directly by phone or email (his contact info is included in the directions).

Good luck!

P.S. – the instructions for the killstick are stored on the PrairieNebraska website we’ve developed as a clearinghouse for information on prairies, prairie management, and prairie restoration.  If you haven’t seen the site, check it out – we hope it’s helpful to you.

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Wildfire Recovery at The Niobrara Valley Preserve – Asking The Big Questions

Most of you are familiar with the wildfire that affected our Niobrara Valley Preserve this summer.  Well, we’re still trying to regain our footing after that event.  A great deal of time and money has already been spent on rebuilding and redesigning infrastructure (especially fences), but there’s still much to do.  In addition, the staff of the Preserve, along with a few of us from around the state, has taken this opportunity to do some deep thinking about what the Preserve can be in the future.  It’s an incredible place, and we want to be sure it lives up to its potential.  I’ll share more about that process as the picture becomes more clear.

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The Niobrara River continues to flow through the Preserve, but much of the landscape looks pretty different since the fire.  Open grassy slopes such as this one will recover quickly, but more wooded areas will come back much more slowly.

In the meantime, we’re also trying to learn what we can from the 2012 wildfire so that we and others can be more prepared the next time something like this happens.  I’ve been asked to help organize this effort, which is an intriguing task for me since most of our questions are about woodlands – not exactly my area of expertise.  Fortunately, I’ve had some great advice from others, particularly Dr. Dave Wedin at the University of Nebraska, who is also generously helping us line up researchers and funding.  Other advice has come from a wide spectrum of foresters, ecologists, and others, and I appreciate it all.

I was up at the Preserve last week for another bison roundup (the west herd this time) and had some time to poke around in the hills and think about our current list of research ideas.  I think we’re honing in on a few important research directions, but we still have some thinking to do about how to ask and answer the right questions.  Since we’re at a good point to get feedback from others, I thought I’d lay out some of what we’re thinking and see if any of you have suggestions for us to consider.  If nothing else, those of you who are familiar with the Preserve, and concerned about the impacts of the fire, can get an update on the situation and a feel for where we’re going next.

Yucca are starting to regrow across the burned portions of the Preserve.  Many show signs of being eaten - there's not much else green out there!
Yucca are starting to regrow across the burned portions of the Preserve. Many show signs of being browsed by deer and other wildlife – there’s not much else green out there!

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Wild rose is another of the plants regrowing in the burned areas.  These woody plants, perennial grasses, and sedges make up the bulk of the surviving plants.
Wild rose is another of the plants regrowing in the burned areas. These and other perennials, including grasses, sedges, and wildflowers, are most abundant in open areas without dense stands of trees.

Our primary research objective is to learn lessons that will help us and others adapt our pre- and post-wildfire management in the future.  It would certainly be interesting to simply document the way in which plant and animal communities recover from the fire, but that has been done elsewhere.  With very limited resources, we’ll spend a little effort documenting how the Niobrara Valley Preserve recovers from the fire (including the use of time-lapse and other photography) but we want to focus most of our effort on learning things that we and others can actually use down the road.

Impacts of Tree Density

The first thing we want to know is how the density of eastern red cedar and ponderosa pine trees affected the way the fire burned  and (more importantly) the way the areas beneath the trees will recover.  In addition to the perennial plants that survived the fire, much of the future plant community in our former pine woodland will depend upon the seed bank (the collection of seeds sitting in the soil, ready to germinate when given the chance).  Unfortunately, areas under dense tree stands are also the most vulnerable to soil erosion.  Especially on steep slopes, wind and water erosion can quickly remove both seed and soil, leaving very little to support plant community recovery.  Since there were few herbaceous (non-woody) plants under dense tree stands, there is little to hold the soil (and the precious seeds in it) from washing and blowing away.  If seeds and soil go, it’s going to be a very long time before anything grows in those places.

Soil erosion will probably be an issue on steep slopes and under formerly dense stands of trees.
Soil erosion will probably be an issue on steep slopes and under formerly dense stands of trees.

We hope to correlate the amount of soil erosion with tree density and slope, and see how those factors affect plant community recovery.  Ideally, we can combine our data with what others have learned elsewhere and develop recommendations for future management.  We want to know how densely can we allow trees to grow before the site becomes vulnerable to severe erosion in the aftermath of a potential wildfire.  Hopefully, that information can help managers decide how to prioritize tree thinning operations.

Much of the erosion that's occurred so far appears to be wind erosion.  A 70 mph wind storm got sand moving in some areas.
Much of the erosion that’s occurred so far appears to be wind erosion. A 70 mph wind storm really got sand moving in some areas.

On a related topic, we want to see how cedar and pine density affected the survival of bur oak trees.  It’s clear that we’re going to have varying degrees of recovery among the oaks growing on the lower slopes of our pine woodlands.  Some of the oaks have already re-sprouted from the base, but others haven’t.  Those others are either completely dead or waiting to resume growth from the tips of their branches next year.  What could we have done as land managers to prevent oak mortality by thinning the cedars and pines near those oaks?

Many of the bur oaks in the burned area are re-sprouting from the base.
This oak is re-sprouting from the base – it’s still alive, but has to start it’s growth over from the ground.

Aiding Recovery

We also have questions about how best to manage the recovery of burned sites.  Some people are advocating seeding burned areas to speed up the establishment of herbaceous and/or woody plants.  There are numerous concerns about this, including what kind of seed would be used and whether or not it would actually make any difference.  We certainly want to avoid introducing plant species that could cause more problems than they solve, but the bigger question is whether or not seeding will make a difference when the most problematic areas are those where soil erosion rates are high.  Putting seed in those erodible areas probably won’t do much good. However, while we and most of our neighbors will probably not be doing large-scale seeding, we might consider a few small-scale trials to test the idea.  We could broadcast seeds in a few trial plots and see if the plant community establishes differently within those plots than elsewhere.

Aside from any seeding efforts, the recovery of ponderosa pines in large swaths of burned woodland is likely going to be dependent upon seed coming from unburned areas.  Because of the size of burned areas, that could take a very long time.  Is it worth trying to speed up that recovery by planting small patches of ponderosa pines in various locations, with the idea that as they mature, those trees would be seed sources for nearby establishment – thus speeding overall woodland recovery?

A few mature ponderosa pines may have survived along the very top of the ridge north of the river.  If so, new pines may be able to spread from these pockets of survivors.
A few mature ponderosa pines may have survived along the very top of the ridge north of the river. If so, new pines may be able to spread from these pockets of survivors.

The answer to that question is related to another big question.  How do we manage these burned woodlands over the next couple of decades – especially in terms of prescribed fire?  At first glance, it might seem that we’ve had enough fire to last quite a while.  On the other hand, prescribed fire might be pretty important to help prevent cedars from coming right back in, and to give us some control over the overall recovery trajectory.  If we do employ prescribed fire, that’s going to impact where pines will be able to survive – including any we plant and those that come back on their own.

Very few pine cones can be found away from the very top of the ridge.  A few isolated exceptions like this might produce a few trees, but future prescribed fires may not allow many of those to mature.
Not many pine cones can be found away from the very top of the ridge. A few isolated exceptions like this might produce a few trees, but future prescribed fires may not allow many of those to mature.

Grassland recovery from the wildfire comes with questions too.  We have choices to make about whether to graze some of those drought and fire-stricken prairies immediately or to rest them for several months or longer first.  In our bison pastures, bison are never removed, so grazing resumed immediately after the fire.  We could build some exclosures to look at how immediate grazing impacts grassland production and species diversity.  In addition, we can manage our cattle pastures in several different ways and measure the results.  What we learn could help us and others make informed decisions after future wildfires.

The last big question we’re struggling with has to do with invasive species, especially in burned woodlands.  I’m not sure yet how to formulate a research question on this topic because we don’t yet know what kinds of invasives we’ll be dealing with.  Some plant species will be much quicker to colonize burned woodlands than others, but whether they will include truly invasive species – and which ones they might be – will be unknown until it happens.  We may just have to be ready to react as quickly as possible when we see what happens, and try to learn from our experience as we attempt to contain any invasions that occur.

We don't yet know what will be growing here in the coming years, but something will - and it will continue to be a beautiful and ecologically important place.
We don’t yet know what will be growing here in the coming years, but something will – and it will continue to be a beautiful and ecologically important place.

There are plenty of questions we could ask about the impacts of this wildfire.  We’re hoping to focus on those that might be the most useful to us and others when dealing with future wildfires.  We have our draft list, but would be happy to hear from anyone with suggestions of other questions we should consider or how we should prioritize among the questions we have.  Thanks for your help and support!

I'm smiling here, but as a prairie ecologist, I'm pretty far out of my element trying to help restore pine woodland.
I’m smiling here, but as a prairie ecologist, I’m pretty far out of my element trying to help restore pine woodland.

If you’re interested in contributing toward the recovery of the Niobrara Valley Preserve, please click here.

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Dealing With a Pervasive Invasive – Kentucky Bluegrass in Prairies

Many of the prairies we manage have pretty degraded plant communities, characterized by low plant diversity and dominance by a few grass species – including the invasive Kentucky bluegrass (Poa pratensis).  Our primary objective for these prairies is to increase plant diversity, which, in turn, bolsters ecological resilience and improves habitat quality for a wide range of prairie species.  Because bluegrass is so pervasive in our prairies, we’ve had to modify our objectives and strategies from those we use to address most other invasive species.

Kentucky bluegrass can stifle plant diversity by crowding out other plants. In many prairies degraded by years of overgrazing and/or broadcast herbicide use, bluegrass is now the dominant plant species and few other plants can compete with it.

When attacking invasive plant species, a common strategy is to contain, and (hopefully) shrink, patches of invasive plants in order to protect plant diversity in non-invaded areas.  In the case of Kentucky bluegrass, however, we have to take a different approach because the species already spans the entire prairie.  Kentucky bluegrass acts like a thick blanket of interwoven stems, roots, and rhizomes – smothering most other plant species beneath it.  Because our goal is to increase plant diversity, we want to make that blanket thin and porous enough that a wide variety of other plant species can grow up through it.   

An illustration of a floristically diverse prairie (left) with several large patches of an invasive plant.  When dealing with many invasive species, we can focus on reducing the size of infestations in order to restore a more diverse plant community.

   

Kentucky bluegrass acts as a thick blanket that smothers most other plant species.  In a case like this, we need to manage the prairie in a way that increases the mesh size of that blanket and allows a more diverse plant community to poke through.

Our primary strategy for suppressing Kentucky bluegrass is the periodic application of prescribed fire and grazing.  We can weaken bluegrass by burning prairies when bluegrass is just starting to flower and/or by grazing prairies harder in the spring than in the summer.  We mix those treatments with rest periods within a patch-burn grazing regime.  The result has been a steady increase in plant diversity in most of our degraded prairies.

If we were fighting a different invasive species, we might expect that if plant diversity was increasing, the amount of territory occupied by the invasive species would be decreasing.  With Kentucky bluegrass, however, our bluegrass blanket is getting thinner, but still covers the whole prairie – something that shows up clearly in data I’ve been collecting over the last decade.  Through the use of nested sampling plots of 1m2, 1/10m2, and 1/100m2, I’ve been tracking plant diversity and floristic quality through time, along with changes in the frequency of various plant species (the percentage of plots in which they occur).  Over the last 8-10 years, as plant diversity within 1m2 plots has increased, the frequency of Kentucky bluegrass has stayed about the same.   Even at smaller plot sizes, which are more sensitive to changes in the frequency of very abundant species, bluegrass is still in nearly every plot.

We also have a number of restored (reconstructed) prairies in and around our remnant prairies.  Within restored prairies, plant diversity is in pretty good shape, but Kentucky bluegrass is rapidly invading.  In one particular prairie, Kentucky bluegrass is now in almost 90% of 1m2 plots and more than 50% of 1/100m2 plots.  That sounds bad, but as bluegrass becomes more abundant, plant diversity – and the frequency of other prairie plant species – is actually holding steady.  There are a few small areas in which bluegrass appears to be forming near monocultures, but for the most part, it looks like bluegrass is just filling in around the other plants instead of actually displacing them.  My guess is that some soil conditions provide such ideal growing conditions for bluegrass, it’s going to be king of those areas no matter what we do.  Elsewhere, however, I think our management is preventing it from becoming dominant.

Here’s the take home lesson for me:  When trying to manage for plant diversity in the face of a pervasive species such as Kentucky bluegrass, it’s more important to track plant diversity than to worry about how much territory bluegrass occupies. 

Just consider the data from our prairies… if I concentrated only on how much Kentucky bluegrass is in our prairies, it would look like we’re failing miserably in our management attempts.  We’ve got just as much bluegrass as we ever did in our degraded remnant (unplowed) prairies, and we’re quickly losing ground in some of our restored prairies.  However, my data also shows that plant diversity is increasing in remnant prairies and holding steady in restored prairies.  Since the ultimate goal is to have a diverse plant community, that’s success! 

Click here to see a PDF showing some of the data I mentioned in this post.

Sweet Clover: Ugly but Harmless? Or Dangerous Invasive Species?

Why is sweet clover the target of aggressive control by some prairie managers and largely ignored by others?  After talking to a number of people across the Midwest and Great Plains, I think there are a couple of things happening.  First, the usually biennial sweet clover can be very abundant and showy in the years it blooms, but is harder to find in other years.  I think some prairie managers see those big flushes and mistake abundance for aggressiveness.  However, I also think that some soil/precipitation/latitude(?) conditions may lead to real negative impacts from sweet clover on plant diversity.

One of the lessons that’s been strongly reinforced for me this summer is that it can be difficult to extrapolate successful prairie management/restoration strategies from one region to another.  Just during the last several months, I’ve visited prairie managers in Nebraska, Indiana, Missouri, and South Dakota and I’ve seen tremendous variation between (and even within) those states in terms of which species are invasive and which are not.  It’s dangerous to assume that just because a species like sweet clover isn’t causing problems in one prairie, it won’t cause problems in another.  I hope we’ll eventually learn enough to accurately predict when to worry and when not to, but in the meantime, it behooves prairie managers to carefully evaluate species at their own sites.

Yellow sweet clover. This exotic species is still planted in some wildlife and ground cover grassland plantings because of its purported wildlife value and cheap seed. However, it appears to be invasive in some places and/or situations.

I’ve been working with prairies along Nebraska’s Platte River for nearly 20 years now, and my observations have led me to conclude that sweet clover is more of a big ugly plant than a true invasive species in those prairies.  Years of data collection on my plant communities support those observations.  That annual monitoring work entails listing the plant species I find in each of about 100 1m2 plots across a prairie.  Those plots are stratified across the prairie so the site is evenly sampled.  Once I have those plotwise species lists, I calculate the floristic quality  (FQI) inside each plot, a calculation that takes into account both the number of species present and the average “conservatism” value of those species.  I can then look at changes in mean floristic quality over time to help me see how the plant community changes over time.  I monitor a few prairies annually, and others on a periodic basis.

Those data show the same thing I’ve seen observationally – sweet clover changes in abundance from year to year (though not as much as it appears visually), but the species doesn’t increase in abundance over the long term and doesn’t appear to negatively impact floristic quality.  Below are graphs from three sites that show both sweet clover frequency (% of plots occupied by sweet clover) and mean floristic quality.  Two of those sites were annually grazed during the data collection period, and the other was only grazed once – toward the end of the sampling period.  Cattle grazing almost certainly helps control sweet clover because it is one of their favorite plants to eat, but I don’t think sweet clover is causing me problems where I don’t graze either.

What my data don’t show is the flush of tall blooming plants that happens every other year or so.  I’m just counting whether at least once sweet clover plant is present in each of my small plots – not how big it is, or whether or not it’s blooming.  Nevertheless, sweet clover frequency changes from year to year but doesn’t appear to correlate at all with changes in mean floristic quality.

Nine of years of annual data from a 1995 prairie restoration seeding. The site has been under patch-burn grazing during each of the nine years of data collection. Sweet clover is never abundant at this site, but has also not increased over time, even through years of drought and heavy grazing. Error bars for floristic quality indicate 95% confidence intervals.

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Sweet clover was present in between 22% and 42% of 1m plots in this restored crop field, planted in 2002. Though the sweet clover frequency varied from year to year, the mean floristic quality of the plant community increased between 2004 and 2008 before leveling off after that - apparently independent of sweet clover. Sweet clover data from 2008 was eliminated from this graph because I later questioned whether I'd confused black medick and sweet clover in some plots. This site was not grazed except in 2009.

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These data are from a remnant mesic prairie under patch-burn grazing. Instead of being stratified across the entire prairie, these data are from a single patch that was burned in 2008, and that same patch was sampled again in 2009 and 2010. It was grazed very hard in 2008. In 2009, no new patch was burned, so it was grazed hard again, but then fenced out in early June. In 2010, the site was not fenced out, but received only light grazing while cattle focused on another portion of the site that was burned. These data are from only about 30 plots per year.

I feel pretty good about ignoring sweet clover and focusing on more invasive species on our prairies.  Both my observations and data support that strategy.  However, as I said earlier, just because the species doesn’t appear to be problematic for me doesn’t mean it isn’t an invasive species in other prairies.  It’d be great if we could compare data similar to what I’m presenting here from a number of sites to see if sweet clover is acting differently in different places.  Without data, it’s hard to know whether or not people are just interpreting the “invasiveness” of sweet clover in different ways.  For now, my answer to the question,  “Is sweet clover really invasive?” is still the same…

Maybe.

Purist or Pragmatist? Identifying and Addressing Non-Native vs. Invasive Species in Prairies.

Recently, there has been a lot of consternation and confusion among biologists and the public about invasive species.  Much of the confusion comes from misusing the term “invasive species”, and particularly the practice of using the terms “non-native (or exotic) species” and “invasive species” interchangeably.  This really needs to stop.

In North America, non-native species are generally defined as species that were not present in an ecosystem prior to European settlement.  There is plenty of discussion to be had about whether or not that is a useful definition, but there you go.  While definitions of invasive species vary, most ecologists use a definition similar to that used by the National Invasive Species Informational Center, which has two important parts.  First, the species must be non-native to the ecosystem in question.  Second, and most importantly, a non-native species must either cause – or be likely to cause – harm to the environment or human health in order to be considered invasive.  That ability of the species to cause harm when it’s been introduced into an ecosystem is the key characteristic that splits invasive species from all other non-native species.

A third term often thrown into invasive species discussions is “weed.”  The common definition of a weed is “a plant out of place” – meaning that any plant that shows up where someone doesn’t want it can be considered a weed.  I don’t have any problem with that definition, but there are at least two problems that arise from using the term “weed” interchangeably with “invasive species”.  First, of course, weeds can only be plants, and there are plenty of invasive species that aren’t plants.  Second, because of the definition, a plant that is called a weed by one person might be a wonderful plant to the next.  Lots of native perennial prairie wildflowers show up in weed books and websites, for example, because the authors of those sites see them as extraneous to pastures, yards, or other non-prairie habitats.  Many other “weedy species” (native and non-native) are important components of prairies – temporarily occupying space abandoned by stressed perennial plants until those perennials recover from fire, grazing, or other disturbances.

Common mullein (Verbascum thapsis) is a non-native plant considered to be invasive in some places, but not in Nebraska. In our Platte River Prairies it appears when dominant grasses are weakened, but doesn't persist when those grasses recover.

Several high profile articles and opinion pieces have recently questioned the value of fighting against species simply because they are “non-native”.  I think it’s a great topic of discussion, albeit one that makes many ecologists uncomfortable.  However, some of the authors – and MANY of those who have subsequently reported on the original pieces – make the very dangerous error of interchanging the terms “non-native” and “invasive” as they discuss the topic.  Even The Nature Conservancy’s Chief Scientist made this mistake in a blog post he wrote about a journal article by Mark Davis and his colleagues. 

Here’s the thing, it’s really easy for those of us working to conserve native ecosystems to become purists about the species we want in those ecosystems.  We are fortunate in North America to have ecosystems that consist largely of the same species that were present in those systems at the time of European settlement.  There are advantages to having ecological systems full of those “native” species because those species have had time to develop relationships and counterbalances with/to each other.  However, very few ecological communities (none that I work with) remain completely devoid of non-native species, and keeping them “pure” gets harder all the time.  Drawing a line in the sand and working to prevent any non-native species from getting a foothold in ecological communities is not only impossible, it’s foolhardy as well.

Don’t get me wrong, we spend a lot of time fighting invasive species in our Platte River Prairies.  It’s by far the most time-consuming and expensive part of our stewardship work – and extremely important.  However, we’re as careful as we can be to prioritize those species that we work against so we aren’t spending time and effort on species that aren’t causing any problems.  (If you’re interested, I wrote an earlier post on prioritizing invasive species.)

As I consider whether or not a particular species is one to attack or live with, I focus mainly on the question of whether that species adds to, or subtracts from, the species diversity, ecological resilience, or ecological function of my prairies.  Does the new species outcompete others to the point where small or large scale diversity declines?  Or does the species actually increase species diversity by adding itself (and its functions) to the prairie?

For example, I don’t worry about plant species like the biennial plant goatsbeard, aka salsify (Tragopogon dubious), even though it’s a non-native species.  My experience with goatsbeard is that it periodically appears here and there in prairies – mainly where defoliation has weakened dominant grasses and opened space for the establishment of new plants.  It certainly doesn’t appear to be eliminating other species or negatively altering habitat.  Rather, it’s inserted itself into the plant community in such a way that someone who didn’t know better would assume it was native. 

Goatsbeard, aka salsify, is a non-native plant species that doesn't appear to be invasive.

In contrast, I worry a great deal about species such as crown vetch and smooth brome, because both can form large monocultures, and if left unchecked, can transform a prairie plant community into one dominated by only a few plant species.  Not only does that affect the plant species pushed out of the community, it severely alters habitat conditions for pollinators and other species that rely on those now missing plant species.  Further, it changes the habitat structure and food availability for many animals.  We try to eradicate crown vetch as soon as we find it, because it’s not (yet?) widespread on our sites.  We know we can’t eradicate smooth brome because it’s already all over the place, but we do design management strategies to suppress it when possible, and to encourage other plant species to fill space left by weakened brome plants. 

We also, by the way, suppress or kill native species that act aggressively and simplify either species composition or habitat structure.  For example, eastern red cedars are native species that encroach upon prairies when fire is absent.  We clear cedar trees that are too large to kill with fire, and use periodic prescribed fire to stop others before they grow very large.  In addition, we use herbicides to kill many other native tree and shrub species, including honey locust, smooth sumac, rough-leaved dogwood, and many others when their presence works against our ecological goals for a site.  Similarly, most of our fire and grazing management is designed to suppress the dominance of native warm-season grasses like big bluestem and indiangrass because those grasses can reduce plant diversity if given the chance.

This eastern red cedar had a short life prior to our prescribed fire that killed it. Cedars are native to Nebraska, but when left unchecked can drastically impact prairie habitats and species diversity.

There are, of course, invasive and other non-native animals too – not just plants – but for the most part, prairies in our areas have few animal species that we know to be causing problems.  There are a few invasive insect species that were introduced as biocontrol for invasive thistle species but subsequently began attacking native thistles – but I really don’t know much about them.  However, a couple of non-prairie birds provide good examples of non-native vs. invasive animals.  European starlings are non-native birds that are a substantial reason for the decline of native cavity nesting birds such as red-headed woodpeckers.  Starlings, therefore, are invasive species.  In contrast, Eurasian collared-doves are a new species of bird to Nebraska, but at least to my knowledge, no one has shown any reason to be concerned about that.  Collared-doves may just be a new species of bird that has successfully joined the community of species in our towns (where they are usually found).

There are, of course, some important differences between non-native invaders like crown vetch and smooth brome and native species like cedars and big bluestem.  Those differences include a long history of inter-species competition that has built plant communities that are unlikely to allow any one species to become overly dominant – or that at least have the capacity to prevent that dominance under certain fire, grazing, or other conditions.  Most successful invasive species are able to invade and dominate regardless of managment conditions, and require direct focused attack in order to control them.  An additional difference is that with native species, we know what we’re getting.  We have a pretty good idea of how they grow, how they interact with other species, and what factors give them an advantage or disadvantage within their communities.  With non-native species, we don’t have that history to draw upon as we try to decide whether or not to control them.  That uncertainty is a huge challenge for those of us who have decided not to be purists about native/non-native species, but to instead work against those species that decrease diversity and resilience.  How do we know which new species will be problems?

Sometimes we can use information from other land managers or published journal articles that have already evaluated species which are just showing up in our prairies.  However, even in those cases, it can be hard to know for sure how a new species will act when it comes in.  Varying soils and precipitation rates are just two of many factors that can lead to a species becoming invasive at one site and simply non-native at others.  Sweet clover is a great example of a species that is considered to be an awful invasive species in some places and simply a big ugly non-native plant in others.  I don’t like sweet clover, but I haven’t seen it decrease plant diversity over time at our sites.  In prairies we manage with periodic grazing, sweet clover is largely a non-issue because it is so palatable to cattle.  In our other prairies, it becomes visually abundant in some years and not in others, and the surrounding plant community seems to be just the same after a flush of sweet clover as it was before it.  I’ve spoken to other prairie managers around the country who see sweet clover as I do, but I also know managers who see it acting much more aggressively.  We’ve made the decision not to worry about sweet clover on our prairies, but I certainly don’t blame others who spend time and effort suppressing it.

Sweet clover is a species that is considered by some to be very invasive, but we tend to think of it as a big ugly plant that comes and goes without lasting impacts. This is a photo I took this summer in some of our research plots where we are tracking sweet clover and other non-native species in high and low diversity plant communities.

This kind of uncertainty about potential impacts creates an obvious conundrum.  We can’t fight every new species that comes into our prairies, but we don’t always know which to focus on and which not to.  Unfortunately, I don’t have any easy answers.  We all have to make our own decisions based on the best available information and the amount of time/effort we can spare.  For example, someone who owns a small prairie and has abundant resources might decide to prevent any new species from joining the prairie community to be completely safe.  On the other hand, most of us are forced to make difficult decisions (guesses?) because our resources are very limited. 

Maybe the key is simply to be thoughtful.  I think it’s a mistake to assume that a species is bad just because it’s new.  Not only are some non-native species fairly innocuous, many can provide benefits, including food sources for native animals, replacement for eradicated native species, etc.  However, it’s also a mistake to look at a few prominent examples of where non-native or invasive species turn out to provide unexpected benefits and assume that we should just accept all comers.  The successful nesting of endangered southwestern willow flycatchers in riparian habitats dominated by invasive salt cedar, for example, has led some to suggest that maybe salt cedar isn’t so bad after all.  This inaccurate, but frustratingly common, misreading of the situation ignores all of the damage to other aspects of the environment caused by salt cedar.  Clearly, there are some species that need to be controlled at all costs before they completely wreck important native habitats.

Salt cedar has been shown to be invasive, in that it has multiple negative impacts on the surrounding environment. Here it's growing in a patch of non-native Phragmites (common reed) - another invasive species.

All of us who manage prairies have to make daily decisions based on best available information, past experience, and gut feelings.  Decisions about invasive and other non-native species are really no different.  I certainly don’t plant seeds of non-native plant species in our prairie restorations, but I also don’t worry about most of the non-native plants that establish there.  Frequent conversations with other prairie managers help me keep track of which species are causing problems elsewhere, and that helps me make decisions about our sites.  I’m sure I’ll make (have made?) mistakes about which species to worry about, but I hope that careful monitoring of those species and their interactions with the surrounding community will help me catch those mistakes early. 

I’d love to have prairies with only native species in them.  I’d also love to have prairies with millions of contiguous acres, large herds of free-roaming bison, and staggering plant, insect, and animal diversity – along with a huge staff of well-trained and well-equipped land managers.  Unfortunately, the reality is that I manage relatively small and fragmented prairies with a small staff and old equipment – and our prairies contain quite a few non-native species.  I try to eradicate known invasive species as they appear, suppress the ones that are entrenched, and make smart decisions about species I’m unsure of.  Anyone have a better plan? 

 For those of you in Nebraska, there is a great invasive species site that contains current events, species lists, and other great information about invasive species.  Visit the Nebraska Invasive Species Project site here