Mark's Burning Questions
Mark H left some great questions in response to my post earlier this week about the fen burn, and I thought I’d respond to them in a full post rather than just replying in the comments. Paraphrased, Mark’s three questions are:
1. You burn annually. Isn’t that a lot?
2. Doesn’t burning remove the ability of decaying vegetation to produce humus and enrich the soil?
3. Does the burning damage other organisms, like animals, on your site?
These questions really get to the heart of why, when, and how we burn.
1. Although we hold prairie burns annually, we do not burn the entire prairie annually. We practice rotational burning, and only torch off a section of the prairie each year. Prior to the burn, we carefully plan which sections of the preserve are to be burned and which are to be left unburned each year. We can control the extent of each burn with remarkable precision. Any given spot on our preserve burns on average once every three years.
2. Part of the answer to the question about humus is also our use of rotational burning The main answer, however, involves differences between prairies and the temperate rain forests around Mark’s home in the Pacific Northwest. Unlike a forest, a significant part of the vegetation biomass in a prairie is actually underground. Dense root systems penetrate 10 to 15 feet beneath the soil. Prairie soils are famously deep and rich- much more so than soils of forested ecosystems. A large part of their formation is the result of growth, death, and decay of these underground root systems. The prairie burn releases a lot of nutrients into the soil, too. The summer after a burn, vegetation in burned areas will be visibly more lush than in adjacent unburned areas. Later this summer, I’ll try to find some good examples of this and post pictures.
3. The effect of burns on animals is a big and complicated question. The concern is greatest where insects are concerned, and therefore is of particular interest to me. A full response is beyond the scope of a blog post. A lot of the work on this issue has been done by my mentor, Dr. Ron Panzer of Northeastern Illinois University. Ron showed that prairie insects are initially strongly suppressed by prairie fires, but that they show great ability to rapidly re-colonize burned areas from adjacent unburned ones. We make use of this information in planning our burns. For example, there are three major remnant habitat types at the fen: fen, gravel hill prairie and bur oak woodland. We never burn all of any of these habitats the same year. We do not go back and re-light patches of unburned vegetation within a burn zone. These are left as insect refugia. And we leave areas where I am doing butterfly restoration alone, particularly while the fledgling population is still small and vulnerable.
Burning is essential for prairie ecosystems, and a useful tool for management. Like all tools, it can be misused and must be handled carefully and with concern for safety, both of the operators and of the prairies that it is being used on.