Refugia

What is Refugia?

Refugia must be intentional and planned. It cannot be left to chance. Why? Prescribed fire kills every insect that is above ground in the area being burned. Immobile insects overwintering in stems, leaf litter, or seedheads are killed when the fire moves through the landscape. If the fire is hot enough, that heat could penetrate into the top few centimeters and harm those soil insects. Knowing this, it’s common sense to plan areas of no disturbance — refugia.

These surrounding undisturbed areas (aka refugia) are how insects repopulate the managed area.

Implementing planned refugia can have complexities, yet these are not overwhelming. Since we are restoring our land to native, we clearly care about our wildlife and insect biota, so overcoming these is a simple matter of planning. We must accept every aspect of this responsibility. We cannot assume our neighbor’s land will provide that refugia. Nor can we assume a contractor will write it into a burn plan. 

Another aspect of refugia is leaving “like habitat;” this is a must. This means the refugia must be the same as the habitat being burned with the same type of plants. At Driftless Prairies, we divide our ecosystems by soil moisture and shade type in order to maintain similar refugia. We have full sun prairies, partial shade in the oak savanna, and a shady woodland area. Within these there are soil moisture levels that grade from dry to wet mesic. We work in sections so no more than half of an ecosystem is affected by the disturbance. When managing our plantings, we divide management areas within that particular planting. Several areas have similar sun and soil moisture levels as other areas but they are different ages and support different plants. It’s prudent to not assume these different areas support the same insects.

Each year we tour our land and review our management strategy; revisions are generally made because nature changes. We do not plan our burns based on the calendar because, as one example, if we have a drought year, less thatch builds up and a burn would be unnecessary and detrimental. As I work on our management plans, I realize I’m hearing fewer discussions today about refugia than 15 years ago. Yet, refugia is more consequential than ever. We’re losing our insects, which makes planned refugia more critical than ever. We cannot live without insects.

Prescribed burn refugia

This drone photo shows about 1/4 of the remnant was burned (the lower right hand corner). It also shows another small management unit outside of the remnant burned. The unburned areas will remain as refugia.

Why is Refugia Important?

Our native ecosystems are more than plants. In fact, plants make up a very small percentage of the biota found in prairies, savannas, woodlands, and wetlands. Of the biota, if we solely look at insects, we have names for about 20% but we do not know the biology for all those 20%! This lack of knowledge makes it imperative that we ensure a safe place (aka refugia) remains when planning all management activities.

When refugia is considered, it’s normally been in the context of prescribed fire but we include it in other management activities, such as herbicide applications and mowing.

Planning refugia when mowing and herbiciding is important. Mowing won’t kill every aboveground insect, it could kill some. Spot herbiciding would be the same but broadcast herbiciding (which we don’t do) could kill many if not all. 

We live in the Anthropocene (a geologic time when humans are the principal force on climate and the environment)  and are experiencing wildlife extinctions at a quickened pace. We can only count extinctions for those we know about, yet what about those unnamed, unidentified species. We don’t know what we don’t know.

We provide this native habitat for the wildlife, therefore we make land management decisions to protect them. Balancing management activities and refugia takes time and planning but we want both the habitat and the wildlife healthy and reproductive.

How Much Refugia is Needed?

This is a question that researchers and science have yet to answer. Because we have no definitive answer to this, we tend to leave 30-50% of like habitat undisturbed.

Hoping small patches don’t burn within a burn unit is too unpredictable and leaves too much to chance. Insects don’t uniformly overwinter in a habitat. We can’t be sure those random patches are where the insects overwintered. Are those patches of the exact same plant composition? Our habitat units often have differing soil types, grading from dry to wet mesic; these support different plants, which support different insects. This is why like habitat is emphasized.

We have an understanding that disturbance in our native ecosystems is beneficial and that management of these important wildlife habitats is imperative if we want them to exist. While there has been research instructing us how often based on litter accumulation, this is ignored in favor of dogma.

Fire management and insects is controversial and divisive, yet it doesn’t need to be. Our insects are imperiled with climate change and habitat loss. Why would we not protect them while we’re simultaneously preserving the very ecosystems they need to survive? If intentional refugia is planned alongside management activities, this controversy is minimized. Respecting the value of our insects by ensuring they have like habitat to repopulate the burned or disturbed area is common sense, caring management.

Prescribed burn refugia

The photo to the left is from our 2024 prescribed burns. We burned about 1/2 of the oak savanna to the left of the road. The other half of this already restored oak savanna remained as insect refugia. 

Then we burned a dry prairie section to the right of the road. We have over 30 acres of “like habitat” prairie that will remain unburned this year. 

We have found that rotating our burns and burning small sections works very well for us. We are not overwhelmed with days of burning. We protect our insects. And because every prescribed burn requires follow up, we don’t burn more than we can handle afterward. It’s a win-win-win for us, the insects, and the ecosystems.

These photos from Winona County, MN reflect the hard work of caring for our wildlife and ensuring there is a safe place for insects to survive and repopulate the area. This burn break was painstakingly put in with a brushcutter and a backpack blower. 

What I love about these photos is how clearly is shows the refugia remaining and the terrain. It precisely shows great understanding and care for the entire ecosystem!

Gabe Erickson took these drone photos.