If you’ve ever walked through natural parks in the spring or fall in Minnesota, you may have encountered blackened areas where the vegetation is charred and burned away. Perhaps you’ve also seen fire scars in trees in areas that seem too well managed or too urban for wildfire to get loose. Both these conditions are indicative of an area that is managed with prescribed burning. 

Prescribed burning, also known as controlled fire, is a restoration and land management technique that has been growing in popularity over the last few decades. It is used for managing prairies, forests, oak savannas, and wetlands all over the country. In Minnesota, prescribed fire helps manage and restore prairies and central hardwood forests. You may have even encountered a prescribed burn during the spring or fall, or seen the large smoke clouds rolling over your favorite natural area as the seasons transition. Here at NRP, we just wrapped up our fall burn season. So as we transition into winter, let’s take an in-depth look at why prescribed fire is so important and so useful tool in the ecological restoration toolkit.

Introduction to Fire Ecology

Fire has been a part of landscapes for centuries. Between lightning-strike caused fires to fires purposely lit for land management by Indigenous peoples, many ecosystems have evolved naturally with fire. In Minnesota, our tallgrass prairies and central oak forests both evolved to depend on fire. Native plants and animals in these habitats are adapted to fire, allowing them to survive blazes that kill off other unadapted species that might outcompete them. Indeed, many plant communities actually encourage fire, or a particular kind of fire. For instance, many native perennial prairie species retain old growth in the form of thick duff layers from previous growing seasons. This grassy duff creates ideal conditions for hot, fast burning fires which kill off shallow-rooted, quick growing weed species. Due to their long root systems, the native species survive the top kill with enough root complex to keep growing and take advantage of the new growing conditions provided by the fire. Without fire, these strategies do not provide the ecological advantage they normally would, and may hurt these species’ ability to compete with weedy and invasive species. Looking at habitats across Minnesota, there are many species in this category--species that have developed adaptation to fire, without which they lose resilience. 

After European settlement, wildfires were often heavily suppressed due to concerns over safety to people and property. Due to these centuries of wildfire suppression, a shift occurred in many fire-resistant habitats. Oak trees became outcompeted by faster-growing maples, hickories, and aspen. Oak savannas became encroached by other woody species. Prairies became prone to weed establishment. All around, invasive and weedy species found a foothold where previously they would have perished due to recurring fire. These shifts in habitats and plant communities occurred all over the country with fire suppression, not just in Minnesota. Fire suppression also led to an increased risk of wildfire due to large accumulations of fuel and dead vegetation material that normally would have burned up with frequent fire activity. 

Faced with these issues, ecologists and land managers began to realize the need for fire to preserve and restore these ecosystems. As a result, the last 50 years or so has witnessed an increased attempt to return fire to these fire-dependent ecosystems through controlled burns. These burns, also called prescribed burns, are purposely lit fires in specific habitats that are allowed to burn under controlled conditions. A team of technicians uses weather conditions, fire equipment, and wildfire management techniques to control the perimeter of a burn unit, preventing fire from escaping into other areas while allowing it to burn naturally in the center of the designated burn area. This allows us to ensure that habitats that need fire to sustain themselves are burned, while minimizing risk to neighboring properties. 

The role of fire in ecology is a topic deserving of a thesis paper--multiple in fact--and there are ecologists and scientists that specialize exclusively in fire behavior and the role of fire in ecosystem management. In short, there’s too much to say about fire ecology in one blog post. Between specific plant adaptations, fire history, the role of Native American tribes in shaping fire importance, fire suppression, differing fire behavior, fire regimes, and prescribed fire techniques, we could write a whole series on fire alone (stay turned, perhaps we will!). For now, though, we will stick to the basics of why and when NRP uses fire for our restoration activities. 

If you are interested in learning more, let us know! You can also check out our website, contact us, and continue following our social media all December for more snippets and photos about prescribed fire.

Why Burn?

We use prescribed burns as a versatile tool for many restoration activities such as site prep, maintenance, or ecosystem recovery. Here is a list of a few of the most common reasons we conduct a prescribed burn. 

Limit Invasive Species: Most non-native species are not adapted to the natural fire regime of this region, while many of our native species are fire tolerant due to adaptations like long root structures or thick bark. Therefore, burning can be useful for controlling invasive or non-native species by giving native species a competitive advantage.

Soil Nutrients: When plant material is burned, the nutrients can be returned to the soil. Prescribed burns act like a reset, enriching the soil with more nutrients.

Site Prep: A recently burned site makes the perfect canvas for planting or seeding. Burning before seeding is a way of mimicking natural successional processes, but allows us to control what kind of plant communities return to the site, allowing us to restore native habitats. The blackened earth also absorbs more sunlight, improving growing conditions.

Oak Regeneration: Oak trees are impressively fire resistant. Their thick bark protects them from low-intensity fires, and their seedlings can survive even partial burning from fire. The hardwood forests of the upper Midwest were historically oak dominated because of fire. Oak trees are very slow growing, and their seedlings can easily be crowded out by faster growing species like maple and aspen. Frequent fire helps oak regeneration by knocking back seedlings of faster growing species that are not adapted to fire. Returning fire to forests through prescribed burning is a key part of oak forest regeneration.

Prairie Maintenance: Prairies are fire-friendly ecosystems. Native prairie grasses and flowers have long root structures that allow them to easily survive fast burning surface fires. Fires also burn off old, dead plant material, returning it to the soil and opening up light for new growth to thrive.

When to Burn?

Every ecosystem is different. Many prairies need frequent burns every 3-5 years, while hardwood forest systems may only require burns every 5-10 years, and boreal forests even less. If the site is a new restoration that has a lot of invasive species present, burning more frequently may be necessary to give native species a competitive edge. 

Burn season in the upper Midwest is typically in spring (March-April) and Fall (October-November). Spring burns prepare plants for the growing season by clearing dead plant litter from the winter, releasing nutrients into the soil, and increasing light availability. Fall burns release nutrients into the soil and can prepare sites for a dormant-season seeding. Summer burns are often ineffective because humidity is too high, or are too risky if hot, drought conditions are present. Winter is often too cold and snowy to burn.

Conclusion--for now

NRP recently finished our fall burn season after a number of successful prairie and woodland burns. These burns prepared sites for dormant seeding, and are readying sites for renewed growth come spring. As the days get colder, we are replacing our fire gear for chainsaw gear as we move into winter tree removal work. However, our fire gear will return in spring for one of our busiest seasons--spring fire season. Returning fire to the natural landscape is not an easy feat, but it’s importance for ecology and habitat restoration is monumental. With each renewed effort to encourage fire in a controlled manner comes a renewal of habitats, plant communities, and ecosystems. NRP is proud to be a part of that renewal effort, and we can’t wait to see what the future holds for fire restoration in these landscapes we love.