Tag Archives: fire frequency

What’s the Best Burn Schedule for Prairies?

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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!

The Role of History In Today’s Prairie Management

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Past performance is not necessarily indicative of future results.

I’m no expert in financial investing, but I’d like to retire someday, so I muddle along the best I can.  As I skim through various financial statements and investment newsletters, I often see some variation of the disclaimer above.  The concise statement emphasizes that while history is important, many factors change over time, and we shouldn’t simply assume that what happened previously should drive what we do now.

I was thinking about this statement and its implications while attending the North American Prairie Conference last month.  During presentations and hallway discussions, the topic of history came up frequently.  How often did prairies burn prior to European settlement?  Were bison only abundant in eastern tallgrass prairies after human populations crashed during the smallpox catastrophe?  What was the role of big native ungulates like elk in suppressing woody plants?

Fire

We have reasonably good data on the historic fire frequency in prairies around the U.S.  How should that information drive today’s prairie management?

Questions like those are fascinating to contemplate, and important to our understanding of how prairies have changed over time.  Which of us wouldn’t jump at the opportunity to step into a time machine and go see North American prairies in the 1400’s or other historic times?  Wouldn’t it be fantastic to somehow find and pore over hundreds of years of data on bison population numbers, plant species composition, elk feeding patterns, and lots of other grassland phenomena?  While, that kind historic data is very limited, mining what we do have is fascinating and instructive.

However, just as with stock market investments, we can’t just look to the past to guide what we should do in the future.  The business world has evolved over time.  Simply investing today in the same corporate stocks that were profitable 30 or 60 years ago wouldn’t make a lot of sense.  Instead, we need investment strategies that fit today’s world.  Many companies disappeared over time because their products became obsolete.  Those that are still around, like General Electric, Nokia, and IBM, reinvented themselves.  Why?  The business landscape changed and they changed with it.

The prairie landscape has changed too.  Row crop agriculture and other human developments have replaced grassland across huge swaths of our country, leaving many prairies relatively small and isolated.  Trees and shrubs have flourished in landscapes where they were once scarce, and woody encroachment into small prairies now comes from all directions.  Many new species of plants and animals have found their way into North America, and some have become very aggressive.  Significant amounts of nitrogen from industrial and agricultural sources now enter grasslands by both air and water, changing soil chemistry to favor some plants over others.  Finally, prairies have endured a century or two of impacts from factors such as fire suppression, livestock grazing, haying, and broadcast herbicide use.  Today’s remaining prairies don’t look or function as they did a century or two ago.

corn

Prairies today exist within landscapes that are dramatically different from what they looked like historically.  Row crop agriculture has replaced grassland across much of the Midwest and Great Plains, and trees, invasive species, and many other factors threaten the remaining patches of prairie.

Big changes to prairies and surrounding landscapes mean that land managers face equally big challenges as we try to sustain biological diversity and ecological function.  For most managers, invasive species suppression is our most time consuming and expensive task.  Because of that, we are always searching for new ideas, strategies, and technologies to help us be more effective and efficient.  The herbicides we use to kill invasive plants were not part of the prairie ecosystem a couple hundred years ago, but I can’t imagine trying to do our job without them.  Similarly, brush mowers and the tractors that pull them are certainly not historically accurate, but they are invaluable when creating firebreaks or mowing down large patches of encroaching brush.

Today, land managers’ decisions about when to burn a prairie should be based on the myriad management objectives we face rather than on what the historic average fire frequency might have been at that site.  In many prairies, managers struggle to weigh the benefits of frequent fire to control brush and other invasive species against the potential impacts of frequent fire on vulnerable insects, reptiles, and other species.  Looking at historic fire patterns can help us understand how prairies developed, but today’s fire patterns need to address current challenges and help us sustain our imperiled grasslands.

Similarly, studying the historical population abundance of bison or elk can teach us about how those species influenced prairie communities long ago, but decisions about grazing as a contemporary management strategy need to be made based on today’s objectives and needs.  I wrote last week about the introduction of bison into the Nachusa Grasslands in Illinois, and attempts to capture the impacts of bison grazing at that site.  I’m sure the staff at Nachusa have been in numerous discussions about what historic bison populations were like in what is now northern Illinois.  The decision to bring bison in, however, was not based on history, but rather on defined needs for habitat structure and plant community management.  Nachusa staff are hoping to see more diverse grassland bird communities, for example, and positive effects on a wide variety of mammals, reptiles, and invertebrates.  They also hope bison will help maintain high plant diversity.  In particular, they hope to increase the long-term survival of relatively short-lived plant species that often disappear over time in restored prairie.

bison

Bison and cattle grazing can be useful in meeting some prairie objectives, but is not appropriate for all sites.

Here in Nebraska, The Nature Conservancy uses both cattle and bison to achieve prairie management objectives.  Grazing strategies are designed with specific objectives in mind, and we collect as much data as we can to evaluate the impacts of grazing on plant and animal communities.  Grazing helps us suppress the vigor of both non-native invasive grasses and aggressive native grasses and foster a more diverse plant community.  Plant species that would otherwise be outcompeted by dominant grasses can usually maintain strong populations under various combinations of intensive grazing and long rest periods.  Both cattle and bison can also help us create a wide variety of habitat conditions, including large areas of both short/sparse and tall/rank vegetation and other areas where patches of short and tall vegetation are intermixed.

Just as with fire, mowing, and herbicide use, the value of grazing as a prairie management tool needs to be evaluated not by its historic role in local grasslands but on its potential utility today.  In many prairies, grazing is not feasible or does not fit with management objectives.  For example, grazing is unlikely to make sense in small isolated prairies where wildlife/insect diversity is limited more by habitat quantity than habitat structure, and where plant composition objectives can be met through other means.  At larger sites, however, grazing may allow managers to provide more habitat variety and/or manipulate plant competition in positive ways.  Regardless, decisions about whether or not to graze should be based upon how grazing might help address current management challenges, not upon historic populations of bison or elk.

Prairie management is complicated and we have a lot left to learn.  We can’t afford to be overly conservative or rely too much on what happened long ago.  Imagination and experimentation are crucial components of adaptation, and we desperately need to keep adapting to new challenges if prairies are going to survive.  Companies like General Electric, Nokia and IBM rightly celebrate their history, but they also have to innovate and evolve to keep up with the changing landscape.  Prairie managers need to innovate and evolve to keep up with changing landscapes too.  Let’s learn what we can from the past but keep looking for new ideas and tactics so we can keep prairies healthy and vibrant well into the future.

After all, prairie conservation is worth the investment, right?