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!

Pill Bug Mystery

Last November, we conducted a prescribed burn at a 3-year old restored prairie.  Two weeks later, I was surprised to be able to photograph green regrowth in that area.  Last week, I revisited the same burned area and got yet another surprise.  Thousands and thousands of dead pill bugs (aka sow bugs, roly polies, wood lice) lay scattered across the ground.

Pill bugs

Dead pill bugs in a prairie burned last November.


The distribution of dead critters wasn’t consistent across the site, but there were a lot of areas like this with big numbers.

After I found the first few, I noticed them everywhere.  White skeletons of pill bugs, lying on top of the ground – sometimes in large aggregations, other times just a few here and there.  If I’d randomly tossed a hoola hoop on the ground 100 times, I bet I’d have found at least a couple dead pill bugs inside the hoop after 97 out of 100 of those throws.


I think these pill bugs were probably Armadillidium vulgare, which is a pretty good descriptive name for them.

When I got home, I looked through my photos from last November to see if maybe the dead pill bugs had been on the ground back then too.  If they were still dark gray, instead of white, I might not have noticed them.  Out of about 30 photos, I did find one bug, and it was still dark.  It’s certainly possible there were many more bugs on the ground, hidden by a combination of their dark color and the remaining ash and debris that has since largely disappeared. I’d like to think I would have noticed that many, but I’m not very confident of that.


A single pill bug can be seen in this photo from mid-November last year.

I like mysteries, but I also like understanding ecological phenomena.  Pill bugs are detritivores; they feed on dead and decaying material on and below the soil surface.  One possibility is that the dead pill bugs had been feeding above ground, within the layer of thatchy dead vegetation, and were killed by the fire.  A second possibility is that they were belowground during the fire, but came up after the fire (maybe it got too cold and/or dry because the protective thatch was burned away?) and then died aboveground.  There are lots of other possibilities as well, not all of them related to fire.

I emailed photos and questions to several entomology friends, asking for help explaining what I’d seen.  None had ever seen something like this after a fire.  Based on their responses, though, my first proposed scenario (above) seems the most likely.  I just wish I’d looked more carefully after the fire last November, though there wasn’t any reason to do that at the time!  One of my friends also mentioned that I shouldn’t lose any sleep over what happened since the pill bugs are an introduced species (native to the Mediterranean region) and could be having negative impacts on the native detritivore community in prairies.

caught in grass

There were clusters of dead pill bugs in basal clumps of grasses like this one.  Maybe they got lodged here during a strong wind?

This is the kind of thing that keeps me interested in ecology.  Something killed a lot of pill bugs in that prairie.  It was probably related to the fire, but I can’t even say that for sure.  If it was the fire, were there other creatures similarly impacted, but in a less visible way? (We try not to burn entire prairies because of this kind of potential impact, especially on insects overwintering aboveground.) What impacts might the loss of that many pill bugs have on other detritivores, on the decomposition process in that prairie, or on other aspects of prairie ecology?  Lots to ponder; I love it!

Has anyone out there seen anything like this before?  Any other suggestions as to what might have happened?


Thanks to everyone who played the plant game this week.  Over 360 people guessed on the first question, and over 60% guessed correctly that “Widespread Panic Grass” was made up.  Nice work, though I did purposefully try to make the first one easy.

The second question got many fewer guesses, only about 200, as of my writing this.  I got most of you on this one.  Almost half of the guesses were for Yerba Mansa, but that’s a real plant, folks.  It’s a rhizomatous semi-succulent plant in the lizard’s-tail family (Saururaceae) – I PROMISE I’M NOT MAKING THIS UP – and is most common in the southwestern United States, but has at least one record in western Nebraska.

The correct answer for the second question was “Jagged-edge milkwort,” which doesn’t exist.  It’s a little tricky because milkwort is a real thing, but there is no such thing as a “jagged-edge milkwort”.  Only 14% of guessers got it right.  Congratulations to you 30 people!

It looks like people enjoyed playing the game, so we’ll try it again in the near future.