Should We Be Conducting Prescribed Fires During Drought?

As we enter a second year of drought in central Nebraska, I’m starting to hear discussions about whether or not it’s a good idea to conduct prescribed fires when conditions are so dry.  I have some ideas about this, but am curious to hear other perspectives as well.

Whether or not to burn in a drought year can be a tough decision to make.

Whether or not to burn in a drought year can be a tough decision to make.

Those of you who read this blog regularly will not be surprised that my answer starts with, “It depends upon your objectives.”

Because prescribed burning is inherently dangerous, it shouldn’t be conducted without a clear rationale at any time, but drought can bring some additional risk.  For example, low soil moisture can increase fire behavior, potentially resulting in hotter, faster fires.  Short sparse vegetation may burn readily, even areas that wouldn’t carry fire under more moderate conditions.  In addition, wooded draws or other landscape features that can usually be counted on to stop a prescribed fire might not do so in a dry year.  All of these factors can be safely mitigated with good planning – e.g., using wider firebreaks, being more cautious when the relative humidity is toward the low end of the scale, and increasing the rigor of contingency plans.  Nevertheless, it’s silly to take risks without good reasons.

When burning in drought conditions, it's particularly important to be conservative.  Extra wide firebreaks, larger crews, and strong contingency plans are all good ideas to consider.

When burning in drought conditions, it’s particularly important to be cautious. Extra wide firebreaks, larger crews, and strong contingency plans are all good ideas to consider.

Apart from concerns about safety, many people worry about the impact that burning during a drought might have on prairie plants.  Burning off the insulating layer of thatch can increase exposure of soil to sunlight, making the soil even drier than it otherwise would be.  That can reduce growth and increase stress for many plant species.  Prairie plants are generally well adapted to that kind of stress, however, and most will essentially hunker down until better growth conditions return.  A few plant species actually thrive when the soil is too dry for their neighbors to grow.  Those opportunists include many annual plants, along with some deep-rooted perennials.

Having said all that, the fact that burning can further stress an already drought-weakened plant community shouldn’t be dismissed.  This is where objectives come into play.  If you’re a rancher, for example, and forage production is a primary objective, a prairie burn that reduces grass growth can be counterproductive.  On the other hand, many Nebraska ranchers use fire to control the encroachment of eastern red cedar.  Since prescribed fire is most effective at killing trees when they’re still small, it’s important to burn frequently enough to keep trees small enough to control with fire.  Nebraska droughts can often last 5-7 years or more, so putting a prescribed fire program on hold during drought could have serious consequences for tree control efforts.

Frequent burning is important to keep cedar trees small enough to control with fire.

Frequent burning is important to keep cedar trees small enough to control with fire.

During many Nebraska droughts, cool-season exotic grasses can increase in dominance because what little precipitation we get in drought years tends to come in the spring, and summers are mostly hot and dry.  Under those circumstances, grasses such as smooth brome and Kentucky bluegrass grow vigorously during the early part of the year and deplete the soil of its moisture before native warm-season grasses get started.  That gives brome and bluegrass a competitive boost.  If you’re using prescribed fire to suppress brome and bluegrass, therefore, it can be particularly important to burn during drought years.  While burning in the late spring during drought conditions might dry out the soil and suppress warm-season grass growth, it will also prevent cool-season grasses from being able to take advantage of their moisture advantage.

From a wildlife habitat standpoint, diminished plant growth during drought years can make tall dense vegetation a rare commodity.  Burning off what little thatchy cover exists can leave some animal and insect species in a lurch.  Here in the Platte River Prairies, we’ve reduced the size of some of our planned spring burns to leave a little extra dense vegetation structure standing – not knowing whether there will be much plant growth this coming season.  However, we’re still planning to conduct the same number of burns we typically do because that burning (and often subsequent grazing) is an intrinsic component of our plan for habitat management.

There are many other considerations regarding burning in drought, but few clear answers.  For example, some pollinators may benefit from an increased abundance of “opportunistic” plants such as annual sunflowers that respond well to both fire and dry weather.  On the other hand, drier soil as a result of burning can reduce the flowering of perennial plants that are important to other pollinators.  As another example, a spring fire can usually increase seed production in warm-season grasses – a nice trick for those of us harvesting seed for restoration projects.  On the other hand, a patch of prairie we burned at the beginning of the drought in 2012 ended up with stunted growth and very little seed production, and we actually harvested a fair amount of seed from a nearby unburned site to compensate.  …It’s hard to know what to do.

We burned this Platte River Prairie in the spring of 2012, hoping to harvest grass seed from it in the fall.  As a result of drought, the grass didn't produce much vegetative growth, let alone seed.  This annual sunflower enjoyed the lack of competition, however...

We burned this Platte River Prairie in the spring of 2012, hoping to harvest grass seed from it in the fall. As a result of drought, the grass didn’t produce much vegetative growth, let alone seed. This annual sunflower enjoyed the lack of competition, however…

As with most aspects of prairie management, deciding whether or how to apply prescribed fire during a drought is a complicated process.  There are safety concerns that need to be addressed, and impacts that may both support and conflict with management objectives.  While it won’t solve all your problems, having a clear idea of what you’re trying to accomplish with prescribed fire can at least help you navigate those complex issues and make sound decisions.

What do you think?  If you’re a prairie manager, how do you adjust your prescribed fire plans during drought?

31 thoughts on “Should We Be Conducting Prescribed Fires During Drought?

  1. Chris – Interesting and complex topic that will interweave between the vegetation component and the driving mechanisms between plants and soil. A quick internet search lead me to some interested publications : Cerda, A. and P.R. Robichaud (eds, 2009). “Fire Effects on Soils and Restoration Strategies” – partially online. These studies were based from wildfires and forest systems. Whereas, Knapp, A.K. (1985) “Effect of Fire on the Ecophysiology of A. gerardii and P. virgatum in a tallgrass prairie” in Ecology leads us back to the vegetative composition within the inherent system of droughts and fire on the landscape. I look forward to others posting thoughts or findings.

  2. Great article Chris. We have discussed this many times and you hit all the main concerns as well as positives of burning in drought. I passed it on to make sure all the other PF biologists got it.

    Kelsi Wehrman | Farm Bill Wildlife Biologist
    Pheasants Forever, Inc. and Quail Forever | 20 N Webster | Red Cloud, NE 68970
    p. (402) 746-2268 ext. 3 | m. (402) 746-0295 |
    The Farm Bill Wildlife Biologist program is a partnership with the Nebraska Game & Parks Commission and Natural Resources Conservation Service.

    http://www.NebraskaPF.comhttp://www.PheasantsForever.org ♦ PF Blog ♦ On The Wing ♦ Fan Page

  3. As you say, it depends on your objectives. Thinking from a perspective of tree/grass interactions, fires during droughts will better contribute to demographic bottlenecks for woody species, as you mentioned for JUVI. Given the evidence that woody species are receiving a competitive advantage due to CO2 fertilization, using drought-driven higher severity fires may be the best option for managing for herbaceous species.

  4. Two comments here, one an obvious consideration, and one based on my experience burning in other grasslands. 1) If your use of fire is carried out as part of an effort to maintain or restore important ecological processes that historically shaped and maintained your system, then it would seem illogical NOT to carry out some burns during periods of drought. After all, based on probability alone, one might expect those to be the times that the system was most likely to have burned in the past. The justification of historical precedence may or may not be your particular reasons for burning your prairies – so as you say, it depends on your objectives. 2) (and somewhat related to #1) In one study, we burned grassland plots biennially for 15 years. Burns conducted in “normal” years pretty much maintained the system as it was when we started the experiment. However, plots that were burned during droughts were markedly affected, as patches of humus-rich O-horizons occasionally burned, adding dramatically to micro-scale heterogeneity. These were not easy burns to prescribe – they tended to smolder for days, were difficult to extinguish, hard to get permits for, and unpopular with the neighbors. Yet I concluded they were far more important from the perspective of shaping the ecosystem for decades to come than most of the other burns. My take-home from this was, go ahead and try drought-burning if you can safely (and legally) pull it off on a small-scale, pilot basis, and pay very close attention to the short- and long-term ecological effects to see if the effort and risk can be justified by desirable benefits to the system.

    • Peter – great comments, thanks for chiming in. The 15 year study sounds fascinating. I’d love to read more about what you learned. Can you send me a copy of any publications you got out of it? Also, did you see the recent Letter in Nature that just came out (MacDougall I’d be curious to hear your thoughts on that as well. I don’t know the ecological system they’re working in, but I bet you do.

      • They were in Garry oak savanna in the Pacific Northwest. I want t look at it one more time before saying anything more, but maybe Peter will say everything important about it first. :)

  5. Andrew’s a terrific scientist, and I know the site well – it is in lowland prairie on Vancouver Island. We collaborated on a big study that used that site along with 9 others elsewhere in the Northwest. I found this paper to be really provocative (like so many of his), but also pretty puzzling, with some results I found startling (to say the least), given my experience with similar prairies in the region. I would be very reluctant to generalize his findings regarding responses of grassland systems to fire very far – I think it may depend enormously on just which species are (and are not) present. Happy to chat with you offline about this – don’t want to bury your blog too much with my ecological musings.
    I’ll see if I can find copies of the papers I wrote based on the plots I mentioned. They were back in my Nantucket days, and were mostly “works in progress” that were suitably (and perhaps appropriately) buried in the gray literature.

    • Peter, I’m one of this blog’s readers who appreciates the ecological musings so don’t hold back. With regards to probability of fire within herbaceous systems, there is evidence that suggest, somewhat counter-intuitively, that fire is less likely during droughts because of the effect on fuel load. I don’t have access to my usual literature search tools but here’s one I fond quickly using Google SScholar:

      • Hello, I am very happy to find this post, I’m fully interested and working in this topic in South America. I agree with Steve in that sometimes drought periods prevent natural fires (and sometimes they don´t). This may depend on the system itself. For example in central-north Argentina, in the dry chaco region we are facing a drought period and our grasslands won’t burn because there is little fuel and a lot of space between bunches of grass (lack of continuity). Yet, at the same time in north-east Argentina (about 500 Km far from here) in the wet chaco region we experienced terrible uncontrolled grassland fires for thousands of hectares. So at eastern, more humid grasslands drought periods don’t have an impact on fuel continuity but they do have an important effect on grass flammability.
        I am looking for literature and experiences about this fire-drought (and also grazing) interactions and effects on grasslands so I appreciate the ones you have suggested. Thank you Chris for the article

  6. Chris,
    Good article – do you have any thoughts as to what we should do with Camp Cornhusker, i.e. “burn or not to burn – that is the question.” Your thoughts.

    • James – It’s been a while since I’ve seen the property, so I’d hate to say. There are portions of the property where smooth brome used to be (and probabably still is) an issue, so burning could help there – but that assumes the fuel is there to carry a fire.

  7. I have heard mixed viewpoints from ranchers. Some really want to implement the burn despite the drought because they have invested in tree removal and grazing deferment. For some landscapes, the planning process is so long, that it can really throw off management objectives and schedules if areas are not burned as planned. Thus is the life of a rancher. Adapt, improvise, overcome. Others really feel that they need the grass and can’t afford to defer at this time. I don’t think they are as concerned with changes in the plant community as they are resting and burning off potential forage. Still others have such a cedar encroachment issue that their viewpoint is- if I wait any longer, there won’t be any grass left to burn, because it will be completely covered with cedar trees. Although this is a slight exaggeration, it does portray the urgency of the situation and how necessity is the mother of invention. Another observation- those that graze more intensively are wiggling nervously right now. Those that graze conservatively have an inherent drought management plan- a very healthy and robust sward of native grasses that can weather drought much more effectively.

    • I work in a protected area in Argentina where the situation is close to what you comment about encroachment. Here the burning plan was delayed so long that woody species became dense and tall, at the same time the grass layer is getting sparce (driving towards the expression “there won’t be any grass left to burn”). We tried a prescribed burn last year but we cancelled it because it makes no damage to the shrubs, just burns the little grass we had. What we are trying now is to cut the shrubs mechanically and see if the grass recover. This can be an alternative when fuel is limited (maybe we will have to cut all the shrubs’ resprouts a second time if drought persists next year) and after that, apply fire when the grass/forb layer recovers. We expect higher damage to woody species since fire will act over the shrubs’ resprouts. We’ll see what happens. And any suggestions to this plan are welcome.

  8. Can’t prescribed burn crews focus on wetlands until the drought is over? It seems a drought would make these easier to burn. Wetlands are probably the most fire neglected ecosystem in the Chicago area.


    • You’re right – they burn really easily. The problem is putting them out. Burning wetlands in a drought probably are among the most troublesome burns you could plan to prescribe. Once that organic layer gets going, you’re pretty much stuck out there until the snows in November finally put it out for you.

      • I did not mean the fens or bogs that have thick organic layers. I was referring to the most common wetland in my area, which are sloughs. The organic material in these wetlands does not accumulate like fens and bogs. They have a mucky clay bottom that won’t smolder forever like the pure peat.

  9. On September 4th and 5th, 2011, our ranch in southwest Oklahoma burned in the Ferguson wildfire that originated in the Wichita Mountains Wildlife Refuge. On July 25, 2012, about 500 acres burned again in another big wildfire. 2011 and 2012 were very dry years with hot, dry summers. Here’s what I have observed:
    On the country that burned once (2011), there has been about a 70 to 80% die off of native warm season grasses. Cool season annuals dominated the burn and that is what carried the next fire in 2012. The twice burned land is still pretty much bare 71/2 months later, with just a little green fuzz of annuals coming back. Prior to the fires the range was in good to excellent condition. We removed 1/3 of the stock in April of 2011 and were completely de-stocked by July 4. The heavy fuel load really made for a hot fire. Interestingly the only part of the ranch that didn’t burn was about 700 acres that we burned intentionally in a prescribed fire during August of 2010. The fuel load was of course limited due to the dry year following, but this is now the only part of the ranch that hasn’t lost grass. We have gone from grazing a yearling to 6 acres along with a flock of 300 ewes, to just the 300 ewes. (This is a stocking rate of 1 AU/58 acres.) ER Cedar has really taken a hit. We had areas burn that I never dreamed fire could penetrate. I’m telling this story to relate my experience with fire without soil moisture. I would be very reluctant to do a burn in these conditions.
    Chris, I enjoy this blog, thanks.

    • John – thanks for sharing the story. Very interesting, but I’m really sorry to hear about the hit to your ranch.

      A couple comments. It’s good to hear that the prescribed fire you conducted in 2010 still has good grass. In some ways, your wildfires acted much like severe overgrazing for two summers would have – they defoliated the range at a vulnerable time, but unlike even severe overgrazing, the fires did so without leaving any aboveground portions of those plants to help their recovery. That kind of defoliation decimates the root mass of those plants belowground and their recovery will be very slow, especially without much moisture…

      I’m curious about your 2010 fire in August. What were your objectives, and did you accomplish them? As is often the case, prescribed fires have very different impacts from wildfires because they are planned and set on purpose to accomplish particular objectives (and are usually conducted under less extreme conditions than wildfires). This is really true in woodlands, of course, where fire intensity can be the difference between clearing out underbrush (low intensity) and crowning out and wiping out an entire stand of trees (high intensity). But it’s also true in grasslands.

      Ecologically speaking, I would expect your native grasses to come back over time, but the length of time that takes isn’t likely going to be much comfort or do you much good over the next couple of years. Hopefully, you at least gained a little ground on cedar? I wish you the best of luck on the recovery of your ranch.

    • This is very insightful. I am going to share this with some local ranchers. I really am interested what would happen in those same conditions if the burn were early in the growing season (time of cheatgrass with several inches of growth, and western wheatgrass and bluegrass with a couple inches of growth- late March in SW NE). Of course the primary forage and target for promotion in these prairies is warm season grass (especially big bluestem). Would the warm seasons come back despite drought? Will there be a flush of warm season annuals (weeds)? I really think fire and precipiation timing are the main factors that will change the plant community in respect to fire and drought.

  10. I agree that fires would have historically been more likely to occur in years like this, BUT we are on the precipice of experiencing conditions like this much more frequently in much of North America (severe-exceptional drought, although with wet in-between). So burning just based on the condition will soon, if not already, have little fidelity to history. …not to imply that fidelity to history is the best course at this point.

  11. Great article and photographs. I’m a fisheries manager, so I don’t often participate in burning – but I am very interested in the use of fire and am trying to learn as much as I can. I hadn’t yet thought about the potentially different impacts of burning during a drought, so I appreciate your thoughts and the comments from others!

  12. Nice comments all. I was hoping to read some comments from P-burn practioners AND any organization that may have a policy regarding burning during drought conditions. I know landowners may have mixed comments based on their land use needs, but many of us involve with prescribed fire are attempting to maintain or restore a specific habitat type. If not, we will need to ask Chris to fill in the void since TNC is active in most states and elsewhere on the planet, especially since Chris hinted he has something in mind already (“I have some ideas about this, …”).

    • Mike, I hope you don’t mind me giving you my thoughts. I’d suggest burning it, this is a unique opportunity for you to see what happens to a three year old planting when it is burned during a drought.

    • Mike, Steve and Chris have given you good ideas. Another thing, if the burn is patchy, don’t worry about it, it’s good for diversity! And you’re right on the money with the timing of burning your young prairie, the general consensus in most references (assuming your fuel load is good) is to burn a planted prairie at the beginning of it’s third year.

  13. My objective for the August 2010 fire was cedar control. The burn was done in cooperation with the Wildlife Refuge. We had a burn plan dating back 4 years that included land on both sides of the game fence that separates us, but hadn’t been pulled off for various reasons. When the fire crew called and said they had the go ahead to do a burn in August I counseled with the folks at the Noble Foundation and our NRCS rangeland specialist here in Oklahoma and decided to do our first summer burn. 2010 was a good year here at our place. We received over 8″ of rain in July alone. The fire went off without a hitch. The temperature climbed to over 100 degrees that afternoon and it took until sundown to finish, because of the size and roughness of terrain, but we certainly were happy with the results. Summer seems a much easier season to find days with weather that fits the prescription. It is hard on people though.
    I think you are exactly correct in your assessment of what has happened since the wildfires and what to expect. Thanks again.

    • I first learned about summer burning from OSU, they push it a lot, mostly because like you said, there are more days available that fit a burn rx. There just usually tends to be a lot more smoke on a growing season burn.

  14. Thanks Chris and thanks to all the commenters. I think most comments I would add have been covered, and I would agree – the objective is the key. There is a huge set of possible objectives out there, which also vary from landscape to landscape and region to region. I agree with the idea of trying it on your own site if you can do so safely and then monitor the changes. In Illinois, we are becoming increasingly interested in open oak woodland restoration and management. .Drought years may provide an opportunity to push the fire envelope a little in some oak woodlands that have moved a little deeper into the mesophication hole. Again, safety and a good prescription are critically important.

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