Difficult Decisions – Growing Season Fires and Other Prairie Management Choices

Would you purposefully destroy the nest of a wild turkey or grasshopper sparrow?  Of course not.  But what if that destruction was a consequence of a land management action that benefits the larger prairie community?  That was the situation we were faced with last week as we mulled over whether or not to conduct a late spring (early summer?) prescribed burn.

Michelle Biodrowski ignites a prescribed fire last week (June 6) at a wet-mesic prairie.  The Nature Conservancy's Platte River Prairies.

Michelle Biodrowski ignites a prescribed fire last week (June 6) at a wet-mesic prairie. The Nature Conservancy’s Platte River Prairies.

In the aftermath of any prescribed fire, there are winners and losers.  Fire rapidly and dramatically alters habitat and growing conditions in ways that favor some plant and animal species and put others at a disadvantage.  Fires also kill some insects and other animals outright.  For example, dormant season (late fall through early spring) fires burn up a lot of invertebrates that overwinter in prairie thatch.  Growing season fires, of course, can kill numerous small animals – especially slow-moving non-flying ones.  We usually don’t see the evidence of those impacts, but when we do, it’s no fun.  Over the years, I’ve seen way too many fried snakes and scorched nests, in addition to animals who suffered injuries from our fires.  It can be tough to deal with the knowledge that I made the decision to light the fires that killed or maimed those animals.

Regal

I’m sure we burned up a number of regal fritillaries in our fire last week because the females are within a few weeks of emerging as adults, and the kind of thatchy prairie we burned is prime habitat for overwintering larvae.  However, we would have done the same damage to those caterpillars if we’d burned the prairie any time between October and July.  Fortunately, regal fritillaries are very common in our prairies, so I know the overall population will be fine.

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garter

Snakes are common victims of growing season fires.  It’s likely we killed some snakes last week, though I didn’t see any corpses as I walked around the next day.  I did, however, find a live red-sided garter in one of the small unburned patches in the middle of the burn unit – so at least one survived…

While it can certainly be deadly to insects and animals, fire is also an important part of our strategies to maintain diverse and healthy prairie communities.  Fire can help suppress invasive species, remove thatch and stimulate vigorous plant growth, and attract grazing activity – among many other things.   Prairies that aren’t burned fairly frequently often suffer from tree/shrub encroachment, excessive build-up of litter, and/or dominance by a few native grass species.  Other tools, including grazing and haying, can be used instead of fire (or in addition to it) but those can also have negative impacts, and can’t replicate everything fire can do.  Knowing that fire can cause problems for some species, we try to minimize those impacts as much as we can.  For example, we usually only burn a portion of a larger prairie so that any impacts are not likely to affect the entire population of a species.

A smooth brome

Smooth brome was mostly done blooming when we burned, and starting to make seed.  I’m not sure how much we sapped the vigor out of the brome (a week or two earlier might have been better) but I guess we at least prevented it from making seed this year.

The main objective for our burn last week was to create an attractive patch of nutritious grass to concentrate cattle grazing in that portion of the prairie – part of our patch-burn grazing system.  We are using a light stocking rate of cattle this year, so we expect the grazing in the burned patch to be selective (the cattle should eat mostly grass) and to favor wildflower diversity by suppressing dominant grasses.  Meanwhile, unburned areas won’t be grazed much at all, allowing them to rest from previous years’ grazing and last year’s drought.  The result should be a messy mixture of habitat types and growing conditions across the prairie that will allow just about every species to thrive somewhere.

We’d hoped to burn the site earlier in the spring, but never got the right weather window to do it.  In other sites where we didn’t get our planned burns done this year, we’re using electric fence to temporarily enclose the cattle in what were supposed to be the burned patches.  The idea is to get the cattle to graze the areas down sufficiently that when we take the fence down in early July the cattle will continue to graze the regrowth (which will then be the best quality forage in the prairie) in those patches for the remainder of the season – similar to what we’d see in burned patches.  It’s far from a perfect subsitute for burning, but it does at least concentrate grazing pretty well in one portion of the prairie and allow other areas to rest.  The biggest disadvantage of the temporary grazing enclosure method is that cattle aren’t very selective in their grazing within that enclosure, so we lose some of the benefits we in burned patches when cattle graze mainly grasses.

patches of green

It was a pretty complete (though pretty slow and smoky) burn last week, but there were a few patches that didn’t burn – mostly in low, wet areas where the thatch was moist enough it didn’t carry fire.  The green strip shown here is at the bottom of a wetland swale and is also where I found the surviving red-sided garter snake mentioned earlier.

After weighing the pros and cons of burning in early June, we decided to go ahead with last week’s fire.  We certainly burned up nests of meadowlarks, grasshopper sparrows, and at least one turkey (a forlorn-looking female was wandering around after the fire).  I expect most of those will have time to re-nest, but that only makes me feel marginally better about it.  I’m sure we also killed lots of insects and some wildlife species.  On the other hand, the burn allows us to move ahead with our management strategy to improve the wildflower diversity of the entire prairie.  That increase in wildflower diversity will benefit a wide range of insect and wildlife species in coming years, as will the habitat structure created in both the burned and unburned patches.  We burned about 65 acres, but left more than 300 acres of the prairie unburned.  Actually, there is much more unburned prairie than that, since there are more than 1,000 acres of unburned grassland on adjacent land as well.  That unburned prairie should be a great refuge for fire-sensitive species and give them opportunities to recolonize last week’s burn over the next several years.

eastern red cedar

This eastern red cedar burned brown after the fire, but it’s unlikely to die.  Experience has shown us that growing season fires rarely “cook” cedar trees enough to kill them.  Even when they turn brown, they tend to green up again.  However, this prairie has had numerous dormant season fires, so cedar control was not an objective for last week’s fire.  We’ll get this one next time.

The kind of difficult decision we made last week is a regular part of land management.  Every management treatment leads to the improvement of conditions for some species but hurts others – often literally.  Just letting “nature take its course” by not managing at all isn’t any better.  An idled prairie eventually becomes dominated by trees and shrubs, along with just a few grass and wildflower species.  That degradation of habitat kills or evicts more animals and plants than active management, which maintains diverse plant and animal communities.

Right or wrong, I guess I’ve trained myself to focus on the long-term positive outcomes of our management and not to dwell on the short-term negative impacts.  I’m not sure if that makes me insensitive or just sensible.  One thing that helps me justify our actions to myself is that we’re collecting as much data as we can about the overall impacts of our management.  If we’re going to make tough decisions that have negative consequences for other living creatures, I want to KNOW that those decisions are leading to the long-term benefits we think they are.  We can never collect enough data to know everything we want to, but we collect enough that I’m convinced most of our management strategies are working as planned, and we constantly tweak those strategies as we learn more.

Ants

The ants in these mounds appeared to survive the fire just fine.  I assume they’ll be able to find plenty of food, and satisfy their other needs, as the prairie greens up around them over the next few weeks.

Regardless of the tough decisions we have to make, I love my job.  I feel good that we’re improving the condition of our prairies, and that we’re sharing successes and failures with other prairie managers so they can do the same.  It’s difficult for me to imagine a more fulfilling career.  I always try to focus on the big picture instead of dwelling on the immediate negative impacts of some of our actions.  At the same time, I try to be ethical about what we do, and not cause harm when it’s not necessary.

It’s a messy world and a messy job, but I wouldn’t have it any other way.

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.