Last week, our crew conducted two summer prescribed burns at the Platte River Prairies. One was around 45 acres and the other was about 15. Both burn units made up less than 10% of the total area of their respective prairies. Weather conditions were mild – temperatures in the high 70’s (Fahrenheit) with wind speeds of 5-10 miles per hour and relative humidity around 50%.

The objectives for both units were the same. Cody (Preserve Manager) wanted to shift grazing pressure to the new burns (and thus away from previously burned areas. He hoped the fire and grazing combination would create additional habitat heterogeneity and alter competition in the plant community to temporarily favor plant species that respond well to this kind of disturbance. Another objective was to continue learning about the impacts of various prairie management options, both for our own education and that of those who visit our sites and/or read this blog.

Whenever I post something about summer fire, I get lots of great questions, so I thought I’d try to anticipate some of those and answer them in the main feed so everyone can see both the questions and the answers. Here we go!

Question 1: Can you describe the two prairies you burned?

Answer: Yes. I’m very familiar with them.

Better Answer: The first site is the remnant described in the above photo caption. Cattle had access to the site (and watched us curiously during the fire) but hadn’t been grazing much because they were focused on a different part of the prairie that had been burned this spring.

The second site is a high-diversity (more than 200 spp in seed mix) restored prairie planted in 2000 with very nice plant diversity. It has been excluded from grazing this year and only lightly grazed the previous couple years, so it was getting dense and thatchy.

Question 2: How does a summer fire even burn? Everything looks so green!

Answer: Yeah, it’s pretty wild to watch. What actually carries the fire is the dead vegetation that has accumulated from previous years – especially the layer of thatch along the ground (see below photo). While much of the green vegetation is consumed, the dry thatch is what really makes it go. Summer fires tend to be slow and very smoky, but both of last week’s ended up consuming nearly 100 percent of the burn units.

Question 3: Isn’t it dangerous to work in that much smoke?

Answer: It’s always risky to work in and around smoke, but yes, summer fires need particular planning. We work extra hard to limit the amount of time people spend in the smoke during a summer burn. On the first burn unit, we made our downwind fire breaks extra wide and used a strong wet line (sprayed water in a strip along the edge of the burn before igniting). That gave us extra trust in those breaks to hold the fire. As a result, after igniting along that line, we could wait and let a lot of smoke dissipate before going in to make sure the line was holding. If it wasn’t, the wide breaks gave us plenty of time to respond and catch the fire while it was still within the mowed break. For the second unit, we used a gravel road as our downwind break, which meant we didn’t need to check that line at all.

Question 4: Aren’t there a lot of risks to animals from a summer fire?

Answer: Yes, but there are a lot of risks to animals with any fire, regardless of season. Dormant season fires consume lots of invertebrates, for example, that are overwintering in thatch or in the stems of plants. Any growing season fire can be dangerous for animals because more of them are active and aboveground than during the dormant season. However, many of those animals are mobile enough to escape the fire (as opposed to overwintering invertebrates – and vertebrates – in a dormant season burn).

Having said that, though, summer fires can obviously present significant hazards for animals. There are ways to help mitigate that. One is to burn only a small percentage of a total area. My personal perspective is that 10% seems about right, but that’s not based on any science.

The tactics used during a burn can also affect the ability of animals to escape. Burning a site gradually so that animals have time (and escape routes) can be better than quickly ringing a burn unit. On the flip side, of course, the longer a burn takes, the longer crew members are exposed to smoke and the more chances there are for something to go wrong, so there are tradeoffs!

Question 5: How does a summer fire affect the plant community?

Answer: It varies wildly, and depends upon a lot of factors – some of which we don’t yet understand very well. Every prairie is different, so it’s hard to predict how a particular plant community might respond to a summer burn. The follow-up management is also important. In our prairies, a summer fire is usually paired with grazing, so the impacts on the plant community are as much driven by the grazing as by the fire.

Without grazing, the effects of a summer fire (without grazing) can be similar to what you’d see from haying. While they’re not identical treatments, both fire and haying remove the vegetative growth plants have produced so far that season. Plants that have completed their life cycle before the event are interrupted in their growth and don’t have a chance to flower or store energy for next year. If the plants more significantly affected are normally dominant within the community, that can open up temporary opportunities for plant species that aren’t strong competitors.

At the Platte River Prairies, our results vary from year to year and site to site. Many opportunistic plant species, including annuals, biennials, and some perennials often flush in abundance for a year or so, but it can be hard to predict which ones will respond in a particular year. Species that may do well include black-eyed Susans, upright prairie coneflower, yarrow, hoary vervain, stiff goldenrod, purple and white prairie clovers, shell-leaf penstemon, and others.

There are a couple species that seem to respond consistently to the combination of summer fire and grazing at the Platte River Prairies. Wedgegrass (Sphenophilis obtusata) usually becomes much more common in our prairies during the year following a summer fire. I’ve only seen Carolina anemone (Anemone caroliniana) three times in one of our sand prairies, and two of those sightings came after a summer burn. Neither of those species depends on summer fire, but they seem to be examples of species that – at our sites – respond well.

Question 6: Why not just burn the same areas in the spring or fall?

Answer: We sure could have, though the results would have been different. In addition, recent springs have been really difficult for prescribed fire and that may be a trend for the future. We’ve had a tough time finding days with appropriate winds and other weather conditions during the spring, so we’ve tried harder to find other burning windows. That’s especially important for sites that are using fire to combat woody encroachment (not really an issue on either of the two units we burned last week). If you need to kill eastern redcedar trees, for example, and can’t get a spring burn done, burning in the summer or fall can still accomplish the same goals.

Additionally, one of our objectives at the prairies owned by The Nature Conservancy in Nebraska is to experiment and learn what we can about land management and restoration. We try lots of stewardship tactics, evaluate them, and have them available for others to come look at during our field days, workshops, etc. There’s still a lot to learn about summer fire, so each one is another opportunity to learn.

Question 7: Will conducting summer fires make me popular with other prairie people?

Answer: Not universally, apparently. I had someone on Instagram respond to a post on last week’s summer fire by calling me foolish and arrogant. Of course, he also said prairies aren’t disturbance-dependent systems, which I would strongly disagree with. Interestingly, he seemed to be in favor of winter burns and periodic haying, both of which I would categorize as ‘disturbances’.

Many people opposed to growing season burns are concerned about changes in the relative abundance of plant species. That’s obviously one important factor, though I have frequently argued that it’s important to manage for a broader set of objectives than just the plant community. If your prairie has rare plant species, however, it’s entirely fair to slant your management toward helping those plants thrive. (On the other hand, if the same prairie also has rare insects with management needs that conflict with those of the rare plants, you’re in a pickle, aren’t you? Prairie stewardship is complicated and hard!)

Regardless, there are certainly people with strong objections to summer fires. There are reasons to be skeptical of summer burning, of course – including some I’ve mentioned above. It’s certainly not something I think should be done regularly or at large scales in most places, but I also think it’s an option worth considering, depending upon your site and objectives. I don’t think a single summer fire on a small portion of a prairie is going to be catastrophic, and it will almost certainly be an opportunity to learn something helpful. A few people might be snarky about it, though.

Question 8: What’s the best time of year to burn a prairie?

Answer: That’s a trick question. It depends upon your objectives, how your particular prairie responds to fire, and whether you’re combining fire with other management like grazing or spot-herbicide-treatment of shrubs afterward. Fire is just one of many options for managing prairies and it should be used intentionally and thoughtfully, especially because it comes with significant risks – for both prairie species and fire crew members.

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Question 9: Do you think prairies are important enough to warrant continued experimentation, especially in the face of rapid climate change, woody encroachment, high rates of nitrogen deposition, invasive species, and other threats?

Answer: Yes.