What’s the Best Burn Schedule for Prairies?

Fire has been part of prairie ecosystems for as long as prairies have existed.  In many parts of North America, prairies both came into existence and then persisted because of intentional and thoughtful application of fire by Native peoples.  Forces such as drought and lightning, intertwined with human management, have helped maintain prairie habitat for millennia.  Fire, people, and prairies are inextricably linked.

Great!  So how often should I burn my prairie?  And what time of year should I burn it?

Ok, hang on. 

While those questions are reasonable in the right context, they’re almost useless on their own.  You’d never ask an experienced baker, “hey – how much flour should I use and when do I add it?”  The obvious response would be, “I don’t know, what are you trying to make?”

Prairie burns should be conducted for specific reasons, not just because the calendar says it’s time to burn.

There is no set recipe for good prairie management.  If prairies are anything, they are dynamic.  That dynamism necessitates an adaptive approach to management.  Burning, like all other management treatments, should be part of that approach.  Every fire should be planned and conducted on its own merits, not as part of a pre-planned schedule.

Weather fluctuations, alone, can strongly influence the growth and flowering of plants.  Insect populations are directly tied to weather as well, but also linked to what happens to plants.  Because so many other species eat, or are eaten by insects, anything that affects them ripples through the entire ecosystem. 

The fickleness of the weather can make a prairie act very differently from one year to another.  On top of that, the behaviors of invasive species, disease organisms, herbivores, pollinators, predators, and other members of prairie communities are also driven by complex, interconnected, and unpredictable forces.  It’s a big, glorious mess.

As a result, the answer to how a prairie should be burned depends on lots of factors. What is your overall objective for your prairie management?  What has the weather been doing?  How did prairie communities respond to recent management treatments (fire or otherwise)?  What are the significant invasive species threats and what influences their ability to become dominant?

This site was burned to control eastern redcedar trees. The timing of the burn was aimed at creating enough localized heat to kill the target trees.

Even bakers don’t always follow a fixed recipe.  Based on how the dough is shaping up, they might add a little extra flour – or not.  Factors like humidity and altitude cause ingredients to act and interact differently and it’s not always possible to accurately predict those responses.  As a result, bakers are constantly testing, learning, and adapting. 

Prairie management has to be even more flexible and adaptive than baking.  Knowing what the average historic fire frequency was in your area is instructive, but it shouldn’t necessarily dictate how often you burn your prairie.  You should be burning when/if it will help you achieve your broader objectives, and if your recent observations show that it would be helpful.

Scientists and historians have estimated historic fire frequencies for most prairie regions.  That’s interesting information, but remember that those are based on long-term averages, which smooth over a lot of variation.  You can be sure the people setting fires centuries ago weren’t gridding out the landscape and deciding when to burn a patch based solely on a regimented schedule.  They burned when it made sense for their objectives, which means some areas surely burned more frequently than others.  Lightning fires, too, would have ignited on irregular schedules, driven by the capriciousness of forces like thunderstorms, drought cycles and grazing.

Historic fire frequencies are mathematic syntheses of irregular events, they’re not instruction manuals.  At their best, they can help us understand the kind of world prairies evolved in.  That’s definitely useful, but the world is significantly different than it used to be, so what might have been appropriate in the past might not always apply today.  Use history as context, not as a template to be blindly followed.

There is much discussion about how common summer fires were in historical prairies. That’s an interesting conversation, but it’s even more important to evaluate what the impacts of summer fires are today and how they might (or might not) achieve local objectives.

Similarly, the optimal seasonal timing for a burn should be based on what you want to accomplish with that particular treatment.  What timing will make the most sense for your objectives?  What are the potential negative consequences of that timing?  The predominant season of fires hundreds of years ago helped shape today’s prairies, but – just as with fire frequencies – that history shouldn’t be the only guide to what we do now. 

With regard to both the seasonal timing and frequency of fires, it can also be important not to get locked into a rigid pattern.  Every fire has both positive and negative consequences.  If you always burn at the same time of year, the same species will always be negatively impacted, and that will surely include some species you don’t want to suppress.  Mixing up the seasonality of burns now and then can help ensure you don’t drive any species to local extinction.

Burning on the same schedule over many years in a row can also cause problems.  Regardless of what frequency you choose, there will be some species that thrive in that regime and others that don’t.  If you don’t ever vary the pattern, you risk losing the species that aren’t suited to it.

Most importantly, be sure there are adequate unburned refuges available any time you burn so you don’t eradicate whole populations of animals (especially invertebrates).  Again, every fire has negative consequences, no matter the timing.  Populations of some species will likely be wiped out, or nearly so, within the burn footprint. 

This beetle was fortunate to find a mini refuge within this fire and will probably survive, but many of its peers might not have been so lucky.

In landscapes with lots of prairie, affected species can probably recolonize from nearby unburned areas – though that process may take more than a year or two.  That recolonization works much less well in fragmented landscapes.  If you burn the only 40 acres of prairie within miles, populations of animals that perish in the fire are unlikely to re-establish.  Even if there is other grassland habitat around, you might have invertebrates in your prairie that are tied to plant species not present in those neighboring habitats.  That will put those invertebrates at risk of local extinction if a burn snuffs out their entire population.

This summer burn covered only a portion of the management unit and there is a lot of other prairie habitat nearby to supply recolonizers from any species negatively impacted by the fire.

Prescribed fire is a powerful force in prairies.  Every fire has both positive and negative consequences, driven by the timing and frequency (as well as its intensity) of its application.  Prescribed burning should be used as part of an adaptive management approach.  Every management treatment (fire, grazing, mowing, herbicide application, etc.) should be applied when it will help achieve objectives and in response to observation and evaluation of what’s happening on site.  After all, smart bakers and prairie managers both know it’s risky to rely too much on a set recipe. 

You might say they both knead to be adaptable and roll with the punches. 

…Or you might not. You might not say that at all.

Hey!  Some of you might remember Evan Barrientos from when he was a Hubbard Fellow about six years ago.  Evan’s doing great work these days as a conservation photographer, videographer, and storyteller.  His latest personal project is called Fireforest.  It’s a terrific examination of the role of fire in Colorado forests – I encourage you to check it out!

Choosing Your Destination Before You Choose Your Mode of Transport

Last week, I attended a science and stewardship conference of The Nature Conservancy in Madison, Wisconsin.  It was an inspiring and thought-provoking week.  There were a lot of topics that will provide fodder for future blog posts, but I wanted to start with an issue that came up in several sessions.  The topic had to do with setting appropriate objectives for conservation strategies, and for land management in particular.  In short, it’s really important to make sure we’re not setting objectives that are focused on strategies rather than outcomes.

This mixed-grass prairie is managed with both prescribed fire and grazing.  However,  neither fire nor grazing is the objective, they are tools that are strategically employed to create desired outcomes.  Gjerloff Prairie – Prairie Plains Resource Institute

Here’s an illustration of what I mean.  If I was planning a vacation for next summer, I probably wouldn’t start with the following question: “What mode of transportation should I take on my vacation next year?”

Clearly, it’s tough to answer that question without knowing more about the ultimate objectives of the vacation.  Where do I want to go?  What time of year am I going?  How many people are going with me?  If I’m planning to travel from Nebraska to Ireland, I probably won’t be able to do that by bus.  I could conceivably travel by motorcycle (if I had one) to the Rocky Mountains, but probably not if I was going during the winter or planning to take little kids with me.

It seems silly to start by thinking about how to get somewhere before deciding where to go, but as land managers, it’s easy to fall into exactly that mindset.  We sometimes set objectives about using fire or grazing, for example, instead of first defining the outcome we want and then thinking about what tools and strategies might get us there (which may or may not include fire or grazing).  In this post, I’ve provided examples of how this trap can present itself, both to managers of conservation land and private landowners, and some thoughts about how to avoid the trap.

Significant research has helped us understand the kinds of fire and grazing patterns under which North American prairies developed.  For example, in many places, we have a pretty good idea how often a particular site burned, on average, before European settlement.  We also have reasonably good information on the presence, abundance, and behavior of historic grazers.  Based on that information, a land manager could decide that the best management for their prairie would be to reinstate, as closely as possible, the timing and intensity of historic fire and grazing that site likely evolved under. 

Historically, prairies in this region probably burned on an average of every 4-5 years.  However, within that average range, there would have been wide variation.  More importantly, this prairie sits within a very different landscape today, with challenges not faced by those historic prairies.

Patch-burn grazing is often described, for example, as “mimicking historic fire and grazing patterns.”  Mob grazing advocates trumpet (though I’m skeptical) that their system replicates the way bison moved across a landscape.  Some in the Upper Midwest region of North America point to research showing high populations of indigenous people and scarce evidence of abundant bison and argue that their prairies should be managed only with fire.  We can argue about all three of those examples – and many more – but the bigger point is that none of those arguments should determine our management strategies.  Again, we shouldn’t be setting objectives about the strategy we want to use without first identifying the outcome we want.

To make a clunky return to my vacation travel analogy, it would be silly of me to choose horseback as my preferred mode of transportation across the Great Plains to the Rocky Mountains just because it’s what worked several hundred years ago.  Today’s landscape is broken up into countless fenced off private land parcels, which would make cross-country horse travel difficult, to say the least.  In addition, there is a pretty nice set of modern opportunities (roads and vehicles) I can take advantage of nowadays.

Likewise, our prairies exist within a different world today, with a new set of challenges and opportunities.  Mimicking historic disturbance regimes won’t necessarily keep prairies in good shape in a world with habitat fragmentation, massive invasive species pressure, climate change, nitrogen deposition, and other factors.  And speaking of good shape, our first and primary concern should really be to define what “good shape” is, right?  Are we managing for plant diversity or a few rare plants?  Are we trying to sustain diverse bird populations?  Habitat heterogeneity? Is ecological resilience the goal?  If so, what are the factors driving resilience, and how to we sustain those?  There are countless reasonable goals for land managers to choose from, many dependent upon scale, but those goals should be based on the outcome we want.

This annually-hayed prairie maintains high plant diversity but provides only one type of habitat structure for nesting birds and other wildlife species.  Depending upon the objectives for the site, that could be fine, but it very much depends upon what the manager wants to accomplish.

I feel it’s important to say this here:  I am a big proponent of both fire and grazing as management tools – you can find myriad examples of that by searching through my previous blog posts.  However, while I think combining fire and grazing can create some fantastic results, those strategies/results don’t fit all objectives.  More importantly, your particular site may or may not respond well to those kinds of fire and grazing combinations.

Let’s say your primary objective is to provide habitat for as many species of grassland birds as possible.  First, you’ll need a pretty big swath of land – many bird species have minimum habitat size requirements.  Assuming you’ve got sufficient land, the major factor grassland nesting birds respond to is habitat structure.  Some birds prefer tall thatchy structure, others like short/sparse vegetation, and others want something in-between.  A reasonable outcome-based objective might be that you want to provide all three of those habitat types across your prairie each year (and you’ll want to make sure the habitat are being successfully used by a diverse bird community).  Perfect.  Now, how will you create those habitat types?

 Grasshopper sparrows tend to nest in prairies with relatively short structure, but with some thatch (which they use to build nests) along the ground.  Some of the highest abundances of grasshopper sparrows around here are found in relatively heavily-grazed prairie.

Fall or spring fires can create short habitat structure that some birds really like to nest in.  However, some bird species (e.g., grasshopper sparrows) usually like short habitat with a little more thatch in the ground layer than is usually found in recently burned prairies.  Also, while burned areas are short and unburned areas are tall, it’s difficult to create in-between height/density habitats using only fire.  This is where other tools such as mowing and grazing might be helpful.  Mowing can reduce the height of tall vegetation and create short or mid-height structure that grasshopper sparrows, meadowlarks, and other species prefer.  Grazing can do the same and can have the advantage that cattle or bison are selective grazers, eating some plants and leaving others.  This can create structure with both tall and short vegetation mixed together and can also help suppress grasses and allow for greater expression of forbs (broadleaf plants) – something birds such as dickcissels often prefer.

Upland sandpipers prefer to nest where vegetation structure is short, but often move to sites with strong forb cover and a little patchier structure when their chicks become active.

If we’re trying to create optimal bird habitat, then, fire, mowing and grazing might all be useful tools to consider.  It’s important to understand how each tool can be used to affect habitat structure, as well as the potential risks of using each (fire can sometimes kill aboveground animals and stimulate invasive plants, grazers can sometimes target vulnerable plants and create issues via trampling).  With all of that information, you can start putting together strategies that employ the right tools, and then test those strategies against the OUTCOMES you desire.  Notice that the process I’ve just described is independent of the kinds of historic fire returns for your area or whether or not you think grazing was a significant factor in the evolution of regional plant communities.  Define your objective by the outcomes you want and test/adapt strategies based on that objective.

Other examples: At my family prairie, we aren’t using prescribed fire because we’ve been able to use grazing to meet our objectives of habitat heterogeneity and increasing plant diversity, and we use loppers/herbicide to successfully control woody invasion.  In small prairies where preserving particular plant species is the objective, a strategy using only fire or mowing could be most appropriate.  If that small prairie has rare insects or reptiles that are especially vulnerable to fire, maybe mowing is the best tool.  Regardless, the right tools and strategies depend upon the outcome-based objective.

This photo was taken in the burned patch of a patch-burn grazed prairie at Konza prairie, near Manhattan, Kansas.  The grazing created varied habitat structure because of the selective grazing by cattle.  Leadplant and other ungrazed forbs contrast with surrounding short grasses.

For ranchers and farmers who manage prairies, this same objective setting process should apply, but of course those prairies also have to help provide sufficient income to keep a family or business thriving.  Even in those cases, however, it’s still important to start with outcome-based objectives.  Those objectives can include a certain amount of needed income but should also include specific habitat or other ecological objectives.  Once you’ve decided, for example, that you really want to manage in a way that provides a certain amount of quail habitat or provides consistent pollinator resources through the season, you can look for ways to accomplish that while still providing the needed income.  When a conflict between income and habitat objectives arises, you can make the decisions that make sense to you, but at least you’re making those decisions with all the information needed to fully consider the options.

Prescribed fire can be a great tool for accomplishing some objectives, but it can also be difficult to implement for some managers.  While it is an important ecological process in prairies, employing prescribed fire should still be seen as a tool/strategy, rather than as an objective in and of itself.

There are plenty of reasonable prairie management objectives to choose from, but they should be based on outcomes rather than on tools and strategies.  Employing more frequent prescribed fire is not a good objective.  However, using more frequent prescribed fire might be a great strategy to reach a particular outcome.  (It could also be a terrible strategy, depending upon your objective.)  Don’t fall into the trap of choosing your transportation method before you know where you want to go. 

P.S. I’m sure some of you are thinking it, so let me address what might appear to be a weakness of my vacation transportation analogy.  Yes, it’s perfectly fine to start vacation planning by deciding that you want to take a cruise ship or motorcycle if the OUTCOME you really want is to ride on a ship or motorcycle.  If you don’t care where you go, the destination isn’t the outcome, it’s just a by-product of your mode of travel.  Fine.  But I think you understand what I was trying to say, right?  Sure, you could argue that conducting prescribed fires could be your objective if all you want is a legal way to light things on fire and watch them burn.  If that’s your objective, though, you’re not managing prairies, you’re lighting things on fire – and there’s a big difference.  Ok?  Ok.