One of the favorite restoration techniques among managers of remnant prairies is fire.
Fire was a natural part of the original prairie ecosystem, so it seemed logical to us to use it in the restoration process. We did several burns in the first few years after we bought our land, but now we’ve come to the conclusion that it’s not a very good tool for us.
The biggest concern I have about fire is that it kills most of the insects in the burned areas. If the insects are flying, they might be able to fly away, but in most stages of an insect’s life, they can’t fly, so they are trapped when the fire comes. When the Indians were burning prairies, there were prairie and savanna areas all around, so the insects could easily repopulate the burned areas. Now most of the prairie is gone – the remnants that are left are like islands in a sea of woodland and cropland. So there are no nearby places for the insects to repopulate from.
People tend to think that plants are the most important part of a prairie, but in an acre of prairie there are more individual insects than individual plants, and more insect species than plant species. Some insects are generalists – they live in many different kinds of environments. They can probably repopulate prairies fairly easily after a fire. But there are other species that depend on these tiny islands of prairie, and can’t live in other environments. We don’t know much about these prairie specialists – which species they are, which species we have here, and what their responses to fire might be.
Ann Swengel has done extensive research into the effects of fire on butterfly populations. She concludes that fire is especially hard on the butterflies that specialize in prairie habitat. The populations of prairie specialists are declining in prairies that are managed primarily by fire.
Another problem with fire is that it doesn’t easily solve the problem of eliminating the invading brush and trees from the prairies. Our remnants have been neglected for so long that the trees and brush are too big to be killed by burning.
And some of the brush is actually stimulated by fire, so we would need to burn annually to keep plants like Sumac and Dogwood under control.
Another big problem with fires is that they can only be done when conditions are just right, and when there are enough people to monitor them so they’re safe. Since we’re so far from everywhere, it’s difficult for us to find helpers, and especially difficult when we can’t tell them exactly which day to plan for. Once we had planned a big burn with 8 or 10 people to help, and that day the DNR put a burning ban in effect for Buffalo County, and we had to cancel everything. So we’ve done almost all our burns with just the two of us.
We’ve burned one of our planted prairies, and two of the remnants, but I don’t think we’ll do more unless it seems necessary.
This was a burn we did on Indian Grass Prairie (a remnant) in the spring of 2004.
The burn a few weeks later.
The results of the burning on this remnant were interesting. In the summer following the burn we saw much more Big Bluestem and less Indian Grass. The grasses grew much taller and thicker than before the burn. Some of the Sumac – but not all – was top killed, and most of the blackened plants sprouted back from the base.
More flowers bloomed, especially Monarda and Purple Prairie Clover.
Hundreds of Yellow and White Sweet Clover seeds germinated (troublesome biennial weeds in prairies).
The second summer the grasses and flowers looked the way they had before the burn – growing shorter and less thickly. The sumac came back from the roots, and seemed as thick as before the burn. And there were hundreds of blooming plants of Yellow and White Clover.
White Clover stalks in the prairie
My conclusion from this experiment is that this one burn didn’t help the prairie in the long run. It would probably help if we did a burn every year, but we have so many remnants, and I’m so concerned about the effects of the burns on insects, that I think it’s better for us to manage our prairies without fire if we can.
If you do plan to use fire on your remnant, I’ve come across some suggestions that may make the burns easier on insects and other invertebrates:
1) Don’t burn every year. Give the plants and animals a chance to recover.
2) Divide your remnant into several sections and only burn one section in any one year. That leaves unburned areas where the insects can repopulate from.
3) Fires usually skip over some areas. Leave those areas unburned – they’ll be refuges where insects can survive.
4) One way to be sure the fire skips some areas is to water them before burning.
5) Leave some areas that are never burned.
The main thing I’ve learned from all my reading is that patchy management may be the best solution – using management tools differently in different places, creating many different kinds of habitat.
I’ve been talking with other people how we manage our prairies, and have read and heard some interesting arguments for and against using fire. Here are a few links to information I’ve found about the use of burning as a restoration tool, and how that affects biodiversity in prairies.
This is a blog post by Ted MacRae about burning remnants. He’s not against burning, but he’s concerned that we’re not doing it carefully enough – leaving enough refugia and paying attention to the insects that live there.
Are We Loving our Prairies/Glades/Woodlands to Death?
Here’s an article about the decline of prairie dependent butterflies, with suggestions on how to change our management practices to do better at preserving rare butterfly populations. ( By Scott R. Swengel, Dennis Schlicht, Frank Olsen, Ann B. Swengel)
Declines of Prairie Butterflies in the Midwestern USA
Ann Swengel has just done a Web Book of her findings and thoughts about conservation of butterfly populations in the midwest. To get to it, go to this page, and scroll down to the section called Butterfly Habitat Management.
Grass-skipper (Hesperiinae) trends in midwestern USA grasslands during 1988-2013 – Ann & Scott Swengel
Managing for Lepidoptera – from the Wisconsin DNR – Great that the DNR is taking this issue into consideration, but it would be even better if they would leave more unburned area – e.g. for Poweshiek Skippers they leave only one unit in five of skipper habitat unburned. This doesn’t seem like enough for a state endangered species. Shouldn’t we be trying to help their population increase?
Michigan Natural Resources Inventory article (PDF) about Papaipema sciata (Culver’s Root Borer Moth) – and other rare Papaipemas – says that Papaipema eggs are very fire sensitive, and fall, winter, or spring burns cause high mortality. “No Papaipema site should ever be entirely burned in a single year. ”
Articles by Andrew Williams, Department of Entomology, University of Wisconsin, Madison
In praise of grazing – Encouraging the use of grazing as a management tool for prairies
Fauna Overwintering in Prairie Stems
A New Paradigm for Prairie Management
Prairie Insect Conservation
Missouri Natural Areas Newsletter – Vol.14, No.1 2014 Prescribed Fire in Missouri
Articles by different authors on the role of fire in prairies, savannas and woodlands of Missouri.
A book just published by the USDA Forest Service: Rare, Declining and Poorly Known Butterflies and Moths of Forests and Woodlands in the Eastern United States, authored by Dale F. Schweitzer, Marc C. Minno, and David L. Wagner has a long section about the effects of fire on Lepidoptera.
Some of their conclusions:
– Sites should be divided into several burn units, and only some of the units burned in any one year.
– There must be sufficient time between burns for recolonization – five years would be a good interval between fires on any one unit to give populations a chance to recover, and for them to start exporting immigrants to other burn units.
Another conclusion they come to – in burning as well as other kinds of management issues – is that patchy management – a mosaic of different treatments – may be most successful.