By Bill Kleiman
Oak species in our area thrive in landscapes with frequent fire. White oak, bur oak, black, Hills oak…. In full sun, bur oaks will grow like this one above with characteristic outspreading limbs. Fires bring sunlight. Oaks love sunlight.
Above, an oak that grew in the open is now crowded in with invasive brush and small trees. The ground layer is reduced to weeds. Oak reproduction stops in such conditions. Brush clearing followed by frequent low intensity fires can reverse this situation.
But oaks can also be damaged a bit by fire when dead branches sit against the base of the tree. When those branches burn they can heat the thick bark of an oak and damage a portion of the cambium layer. The tree likely won’t die. The bark will heal over the fire scar. For sure, it is better to burn the landscape and accept some bark damage than not to burn. If an oak woods is not thinned, or burned the oaks will die out.
Above, is a tree “cookie” that I viewed last week at a fire ecology class in Arizona. We were visiting the University of Arizona Tree-Ring Lab which is the biggest such lab in the world. I forget what tree species it is. Each of those years there was a landscape fire that left a small fire scar that healed over with new bark, but the fire left its tell tale sign.
We toured the lower level where thousands of tree cookies are stored for researchers to come and look at fire scars. Something like 250,000 tree cookies from around the nation have been carefully studied. The story they tell is a continent of landscape fire set by humans and lightening for thousands of years.
So fire scars are ok, but I really like this old oak. Let’s save it from that nasty scar. The branches in this tree are abundant. It takes a chainsaw and a few minutes to move those branches off the base of the tree. If you have just a handful of oaks perhaps you can justify this effort. I enjoy clearing them, having conversations with trees. ”Your welcome” I say with a pat.
In this restoration we found about two dozen small bur oaks growing on several acres where we brush mowed and sawed out cherries, mulberry and box elder. I used the leaf rake to clear around them. It took about 15 minutes. I am using a fire leaf rake from Forestry Suppliers. They work great and hold up to vigorous use. If I had not raked around this young tree the heavy thatch that had built up might have top killed the oak. The tree would re-sprout which is what an oak does, but then I would have to wait several years for it to reach this size again. Bur oaks have become uncommon enough to motivate my raking.
Susan K helped me clear some cherries from this area. We bucked them up for fire wood for next winter.
All those shrubs out there are bur oak, in this case planted as acorns in this prairie restoration by us a decade before. This prairie is frequently burned and the oaks simply re-sprout each time. They must have prodigious roots by now. At some point in the future we won’t burn for several years and a bunch of those oak shrubs will become small and then perhaps large majestic oaks.
grassland restoration network 
At some point you might miss a single year or two years and find that some of those bur oaks get through it. At Sugar River Savanna near Madison, which has been burned 47 of the last 50 years white oaks are having to be manually cut to reset them, because they are resprouting vigorously and even the very low rate of them getting above fire is proving to be too many–a first world problem that took several decades of that management to become evident.
Sounds right. I have another unit where we burn frequently and maybe one percent of the oaks have left the shrub stage and are small trees. They may end up as those majestic adults. And I have a few places where the black oaks are “dog hair thick”. A bit of this is fine. I don’t want every prairie to turn into a savanna. I know you had an essay about embracing shrublands as that is what is coming. That also sounds right. Some grassland birds and others want no trees nearby.
Embracing shrublands had to have been someone else. Brush has its place, but I don’t believe that we have to or should embrace. I do a lot of telling people to cull out over-abundant oaks. Most people have trouble bringing themselves to do it.
Maybe not you, or I read your essay backwards, but the writer was not happy about shrublands… but pointing out that is can be hard to keep prairies free of shrubs.
Are these tiny oaks grubs or planted seedlings?
In the handful of reconstruction sites I manage, scattered seedlings were planted in the forb heavy prairie planting. Each fall we clip 6 feet around each tree. Deer protection had been in plastic tubes–a bad idea. Now we use wire cages which don’t melt. While little fire reaches the stems, the radiant heat often top kills. One practitioner in Missouri suggests a 15 to 20 yr burn moratorium. Not an option for reconstruction. Beginning this year, we will try annual burns rather than every 3 or 4 yrs. The thought being to reduce heat by reducing thatch build up. If any one is interested in exploring effective practices to keep fire on the ground yet allow planted oak seedlings to thrive, let me know.
When we plant bur or white oak is usually is by acorn, as in that one photo with all the shrubs. The oak hand holding is for small areas.
Hi Mark, to reduce the fire intensity on planted trees in savanna reconstructions, we have been experimenting with burning under “cool burn” conditions – i.e., humidities above 50-55%, moist ground, and using backing/flanking fires only to reduce radiant heat (no head fire). It has been challenging to get our fire crews to have patience with burning like that (it’s slow!… and we like to burn fast), but it has worked well where and when we’ve managed it. We have also mowed breaks around the trees as an extra layer of insurance, but that takes a lot of time and I’m not sure if it’s that helpful since the unmowed tuft of vegetation right around the tree often catches fire under normal burn conditions. Also, as a longer term measure to reduce fire intensity around planted trees, we’ve been planting wood betony around them, but (up to 10 years later) the wood betony colonies are not yet big enough to reduce fire intensity enough to keep the trees from top-killing during fires. Good luck with your savanna reconstructions – they’re challenging!
Thanks Bill, Good information as always. fran
Great tutorial, Bill
Waiting for seeding oaks to attain sufficient size to survive a prescribed burn can take more than “several years.” After more than a decade I grew impatient and constructed “heat shields” which I place around small oaks prior to a burn. I construct them from 4-5 ft high rolls of heavy-duty galvanized corrugated roofing metal. I double wrap them around the tree staying 2 ft from the truck and secure with rebar. Double wrapping and leaving an air space between the two layers is crucial because it prevents radiant heat transfer. Requires a bit of work but survival rates are high.
Hi Bills,
Thanks for the article. I just planted a young burr oak here and am very excited and hope it will do well. They are an amazing species. I wish I had the funds to plant a million young trees! This one is about 8′ tall so I don’t know how old it is.
Which place are your photos from?
Suzanne
Across from our HQ driveway on north.
Thanks, but I don’t remember, is this at Nashua grasslands?
Yes. Nachusa
Great thx. I haven’t been there but it looks great.
Suzanne
Hi there – This note is for Bill Kleiman. We met last fall at the annual festival at Nachusa. I am interested in bringing my seed team down from Taylor Creek Nursery sometime in the late Spring. Would that be of interest? I was hoping for a tour of your seed refining area as we have had a great seed refining season and have made some pretty impactful upgrades that might be of interest to you. Let me know what you think! Thanks – Matt Sheaffer
Matt, email me bkleiman at tnc dot org