Why We Burn

May 8, 2017 at 12:57 pm
By Keaton Tremble

Arb Crew and Fall Burn
As you may have noticed a few of the prairies around campus have been burned here in the last couple of weeks. Recently, I’ve overheard some of my friends talking about these burns and several of them (essentially all of them from California), really couldn’t wrap their heads around why we’re burning. I mean, the state of California is engulfed in flame on a yearly basis and these rampaging fires destroy hundreds of homes every year.

Fire is a key characteristic of prairies and savannas here in Minnesota and around the world. Essentially, these habitats have evolved to burn hot and often. When you’re standing in a forest versus in the prairies, where are you most likely to get sunburned (unless you’re me and then it’s possible everywhere)? Prairies, and the species that live there, thrive in high light conditions and have evolved ways to survive and support fires which maintain this light availability! When this light goes away, the grass cannot grow and the prairie no longer is a prairie.

Grass species such as Big Bluestem have huge root systems that can store a lot of energy for when everything above ground is burnt, allowing them to sprout after fire, and the dead stuff that accumulates every year is really flammable material. However, when the prairie hasn’t burned in awhile, trees can begin to encroach on the prairie. Because trees have a lot of their living “stuff” above ground at all times (the trunk and branches) and don’t die back every year like most prairie plants, trees are more vulnerable to damage by fire. When fire hasn’t occurred in a while, trees can begin to grow in the prairie, and shade out the grasses below them. When the grasses are gone, you don’t have the same amount of good quality fuel, which will prevent more fires in the future. This feedback loop where trees grow, prevent fires, and then more trees grow is called woody encroachment and is happening globally. Without fires on a regular basis, our prairies would soon become forests.

Keaton Tremble ’17 for the Cole Arboretum Naturalists
Photo credits: Teaser and On page- Berett Wilber '14

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