Burning prairies is good for native prairie plants and bad for butterflies. That’s what just about all of the guidance for rare butterflies says. It’s the conventional wisdom. Those that question it are reluctant to do so. Allow me. I like butterflies too.
Let me build from an anecdote. In the summer of 2003, I had my first experiences on prairies with regal fritillary butterflies as an intern doing botanical inventory, seed collecting, and management in west-central Iowa. These were were postage stamp, remnant prairies, generally a few to 15 acres in size, and utilized for seed / genetic resources. They were burned frequently by their manager, and a few of them still had large regal fritillary populations. These are large, active, beautiful butterflies. To share a meadow with them is a life experience.
If people knew the beauty of the regal fritillary, they would care about it as they do monarchs. I’m ashamed to say that I never actually photographed one, so I’m reduced to finding an image in the public domain.
So I went about my summer bagging the unripe capsules of prairie phlox to catch the seeds upon explosion and painstakingly gathering not-insignificant amounts of seeds from prairie blue-eyed grass and Leonard’s skullcap, but when I staightened my back, I watched the regals gliding over the prairie.
These prairies were loaded fritillary host plants–prairie violet, bird’s foot violet, or both. There was also no shortage of nectar for butterflies in flight.
Researchers from Iowa State had been on one of the prairies to study the regals. Among other things, research in Iowa has shown that the regals don’t leave the prairie. They fly over the prairie, but if they come to a row-crop field, they turn around. They don’t cross tree lines either.
These prairies were healthy, and they were getting healther. One site, which seemed mediocre when I visited it in 2003, because it was more tham half smooth brome, had become probably the best mesic prairie I’ve seen to this day with frequent, if not annual, spring fires.
In 2009, after several more years of annual burns, the prairies were still there, and so were the regals. The prairies were better than ever, the regals certainly no worse.
This brings me to the science. Much of the older science, which still informs management recommendations for accomodating regal fritillaries today, was speculative. Fire has to kill larvae. Right? They don’t reside underground. There must have been some extremely efficient dispersal and meta-population stuff going on when much of the regals’ range burned frequently before Europeans began their misadventures in stewardship. Or not. At Konza Prairie, in the Flint Hills of Kansas, where I was based in graduate school, and where I also had the privelege of sharing prairies with regals (and slender glass lizards, collared lizards, ornate box turtles, bison, and prairie chickens), host plants were common. Regals were common. Many areas with regals were burned frequently.
Most lepidopterists would be aghast. It’s a moonscape, black and barren.
Well, over the last decade, people have started looking what is going on more close, starting at Konza and the Fort Riley Military Reservation. There, a research team concludes:
“Our results indicate that greater host plant density and short fire return intervals are important to the occurrence of late-instar larvae and despite current management recommendations, larvae may be negatively impacted by a lack of fire. Preliminary analysis of adult data suggests that adult density was greater in areas that were grazed and had a 3-5 year fire return interval. The conservation management implications of these results to the persistence of regal fritillary populations within the region may require a re-thinking of previous assumptions.”
Looking deeper into their research, published in the Journal of Lepidopterists, it seems like larvae are present even following fires in burned areas. How? Larvae were obsered to burrow down or hide under rocks, which is sufficient to survive a quick-moving prairie fire, and apparently they survive until their host plants resume growth (which is pretty immediately). An interesting aside–regals are also utilizing other common violets (Viola sororia) on Konza. That raises other questions, which I’ll leave. I am not at all surprised by the fire response though. Regals are a prairie species. A few might die, but their host plants and nectar sources are more important in determining how well they do than any stress fire puts on them, and not having fire really diminishes their host plants, which get burried in grass litter and die.
Here in Wisconsin, regals are endangered, and Wisconsin Department of Natural Resources guidance suggests that things might be different:
“Grassland management activities must be adjusted where regals are established in order to maintain the populations. Sites that experience frequent controlled burns (less than 5-7 year rotation) exhibit reduced numbers of butterflies therefore burn management should be avoided on regal sites.”
We have newer information for Wisconsin, which frankly makes a lot more sense. Henderson, Meunier, and Holoubek published research in Biological conservation that reaches this conclusion:
“Burning every 3-5 years maximized regal fritillary abundance, but even annual burning was more beneficial to regal populations than no burning at all. Unburned refugia are important in maintaining populations, but creating and maintaining high quality habitat with abundant violets (Viola spp) and varied nectar sources, may be the most impactful management and conservation tool. Regal fritillary butterflies were consistently more than twice as abundant on high quality habitats and this relationship held across, and often dwarfed the effects of, various prescribed fire regimes or climate variability.”
So when we are considering this species, which we should care about (though it is extirpated within my professional realm), considerations for maintaining the habitat are most important.
Now we arrive at philosophy. Our natural resource base has been so degraded, that reductionism, which is the consideration of particular species that are still hanging on for some reason or another, is growing. The guidance still in force is reductionist. It’s about butterflies and potential direct impacts to them. It ignores ecology, that the butterflies are inextricably tied to a system, and particularly to the success of their host plants and nectar resources (though these also have intrinsic value). We cannot manage for regals without considering the system as a whole. We also cannot manage for regals without considering evolution and the arc of time. Regals, their host plants, and their nectar plants existed long before we were here, indeed they existed even when much of their range in thee Midwest was under ice. Their connections are deep and long-standing, but insofar as the old worlds they occupied seem alien, it offers hope for the future…and apparently more host plant flexibility than we knew (which might explain the extirpated Cedarburg Bog population). Maybe we can slowly bring back the summer flights of the regals and add more romance to peoples’ lives, if we also consider the other key elements (fire, violets, and nectar, all things we get from well-managed prairies), and think beyond the species.
As an addendum, I can’t help but think of the Powashiek Skipperling, a much less charismatic, but no less important, lepidopteran that is federally endangered. Several miles to my south, years of burning and brush cutting brought back some prairies from the brink, and the poweshieks, which apparently had persisted in low numbers came back. Then came concern. Burning in the core areas stopped. Powashiek’s primary host is prairie dropseed, a very conservative grass with high affinity to high quality, undisturbed prairies. Prairie dropseed thrives with fire. Without it, it burries itself in it’s own litter; it survives, but in a much less productive state. Also, many of the potential nectar species while Poweshiek’s are in flight flower much more abundantly in years after fires.
The last flight of the Poweshiek Skipperling in that place, despite survey efforts, was four or five years ago now. Poweshieks are grassland butterflies. I can’t help but suspect that the best intentions squandered that opportunity. There is some, but not much, research that addresses Poweshiek’s response to fire. I have to say it’s dubious in terms of inference, given the type of data collected. The greatest deficit, I think, has been a failure to consider the resources that species depends on and what actually happens to larvae, and how many, when their prairies are burned.