Fire For Woodland Restoration and Management

I received this question from John in Minnesota:

“I have a small patch of maidenhair in a woodlot I’m restoring. ‘Restoring’ means getting rid of buckthorn over the last few years. Maidenhair Fern, Jack-in-the-Pulpit, May Apple, Bloodroot, Hepatica, Wild Ginger and 1 Trillium have showed up. I was wondering what fire would do in this situation. I didn’t get to burn it this fall and wonder if fire would kill the fern and the other spring plants if I burned in spring. I didn’t notice the new ferns coming up this fall as is shown in the YouTube video but they look very vulnerable to fire in the fall as well.

I answered:

Burning can certainly help to rehabilitate a woodland. All woodlands had some sort of a historic fire regimen. Perennials such as the Maidenhair Fern will not die from a single fire. The growth point of most natives is about an inch under the ground. You can damage initial growth and that may set the plant back a bit for that season but generally one hit from fire on most herbaceous perennials is no problem. Certainly the timing of the fire can minimize the damage. Prescribed fires for managing a native ecosystem can occur in the fall through winter and spring. You really just need dry (but not too dry) conditions.

Burning management can help the health of a native woodland for several reasons. By clearing the leafy detritus, soil is bared which provides the forbs and other herbaceous perennials with maximum sunlight for a period early in the next season. Seedlings benefit the most. Woodland forbs can take several years to come to maturity in a garden situation where the competition for light and other resources is limited. In a true woodland setting where the leaves are covering the seedlings it can take many years for a seedling to become a mature plant and it will have many opportunities to die during those years. Light and the warmth the fire provides at the ground level will also help seed to initiate germination.

Another way that fire can be a tool to help restore a native woodland is by setting back the woody encroachment: native, not native and invasive-exotics alike. It doesn’t happen as fast nor as thoroughly as one might hope. The buckthorn is going to come back. A fire may kill back the smallest of seedlings. I am often struck by the small girth of woody species that seem unfazed by the fire. It seems to me that any buckthorn tree that is over an inch or two in girth needs quite a hot fire to be damaged. A regular burn cycle may be needed for several years while the ecosystem continues to heal.

Burning a woodland can be very different from burning a more open ecosystem such as a prairie. I think of the time Bill Carter and I allowed a prescribed prairie fire to slowly creep into the adjoining woodland. The raging prairie fire quickly tamed down into a slow trickle of flames that slowly danced through one leaf at a time. We had to encourage the fire over downed logs. We eventually had to stop the slow progression and go home. Mostly we just stepped the fire out with our boots. It had advanced maybe fifty feet into the woodline after an hour or so. I can’t imagine the low intensity of a fire such as that setting back any but the smallest woody seedlings.

I also remember watching from across the valley as an old dead oak snag that was probably twenty feet high and maybe three feet in girth was shooting flames into the sky like a Roman candle. If a woodland has not seen fire for over one hundred years there will be tremendous tinder build-up. Long-burning hot fires can sterilize the soil of the native seed bank and any living plant. Physical restoration and removal of the fuel may be the first very hard step in a woodland restoration. It could certainly be argued that the downed timber acts as habitat but most of our woodlands have too much of that kind of habitat and could be the reason why we have such a plethora of certain species like rabbits.

It can surprise people that fire was historically a part of natural woodland ecosystem management. Woodlands evolved with fire. The composition of these ecosystems is a result of a regular occurrence of fire over thousands of years. In most cases, do not picture a cataclysmic canopy fire, although that was certainly one kind of fire that may have occurred in some woodlands historically. Fire would burn just the ground layer typically.

The aesthetic appeal of a healthy woodland that has had an occasional fire is very different from a woodland that has accumulated decades of brushy brambles and volunteer trees that fill in every bit of the canopy. A degraded woodland can be rendered impassible with brush, especially now with the very aggressive woody species such buckthorn, barberry, and honeysuckle. The ground level species in a woodland can suffer from this filling in. If a woodland was historically fairly open,it may have had a species composition on the ground level that was fairly light dependent. When the woodland then fills in, those light-dependent species will eventually die out and if there was no appropriate seed bank of shade-tolerant species available to replace them, you can end up with a very low-diversity woodland floor that is vulnerable to encroachment from invasive species. It is not uncommon to see “natural” woodland situations where the ground level is dominated by just a few species. This is most likely a situation where the trees fast filled in when fire succession came with the settlers. Early unbridled grazing also probably influenced the low diversity.

Fire is a tricky phenomenon as management tool. The social and safety concerns make it a near impossible option in many situations. In a small woodland that is actively being restored to appropriate (and attractive) native vegetation, small highly controlled spot fires that are immediately extinguished are an option. It is always important to follow local fire ordinances with all due caution.  (we sell this book ‘Managing Small Prairie Fires’ in our online store for $6.)