Reading Stumps for Clues

A stunning record of violence, disease, and more is recorded in the stumps of trees.

When we cut over-abundant trees to restore space for oak reproduction and to generally restore health to the woodland, a graphic history emerges.

Here, in Somme Prairie Grove Nature Preserve, the stump above was the first to catch my eye. A hickory in an oak woods needs to contend with burns. This one was severely scorched twice - and then largely recovered. In those thick black areas, the living phloem and cambium were dead. If you look carefully, you can see the very wide growth rings where the tree was racing to heal the wound. 

Conservation note: if burns are mild (not very hot), large numbers of hickories may replace oak reproduction. Oaks win out only under the influence of hot burns. 

In the case of this tree, the wound was so severe that it hasn't healed yet, after more then fifty years. If those widening rings had successfully met and healed the tree's circumference, it would have ended up as a hollow tree (perhaps to the pleasure of flying squirrels, raccoons, bats, and others who like to live in them). 

In the case of this one, I've hyped up the contrast so we can see the rings better. After two thirds of the living outer wood was killed, it took 16 years, by my count, for the tree to heal all the way round. Where it did heal, a little black scar sticks up to mark the spot. The impacts of less severe burns now and then show up here and there.

This one shows a lot of purple - and many burns and many healings. The purple is herbicide - to prevent this stump from re-sprouting and healing again. Why, some people will ask, would anyone cut and herbicide trees in a Nature Preserve? Or burn the place, for that matter? For more on that, check out The Somme Experiment and Why Cut Trees?

The stump above is of a bur oak. We cut down dozens of trees - oaks (bur, white, red, and Hill's) and hickories (shagbark and bitternut). In this preserve, restoration management has gone on for just over 40 years. Decades ago we cut most of the the invasive buckthorn, box elder, black locust, and others. We didn't expect to still be cutting here, as the controlled burns would likely do all the thinning needed. But they didn't.

This "before" photo ...

... shows the problem. The old trees (wide trunks and horizontal limbs) typify the natural trees of an open oak woodland. The surrounding scores of thin, limbless young trees are a pathological result of no fire for many decades and, more recently, insufficiently hot fires. Bur oaks are much less likely to be damaged by fire as seriously as a hickory (or even most other oak species, to a lesser extent). Because of safety concerns in the metro area (or anywhere these days?) it's not possible to do prescribed burns on sufficiently hot, dry, and windy days to thin out the bur oaks. We could wait until most of them were killed off by the others, but that doesn't work for the rest of the ecosystem. The grasses, wildflowers, pollinators, ants, soil biota and myriad others that comprise the rare biodiversity of the oak woods would be increasingly lost, as some already has. Thus we cut.

This is a bur oak stump cut a few years ago, where bur oak pole trees were dense. Today I count at least 27 young, aspiring trunks rising out of it. This is what bur oaks do, after fire or saw. They're accustomed to setbacks. In the photo below of the same stump...

... you can see a couple of those trunks now reaching six feet high. There are still too many trees (too much shade) for a fledgling bur oak to be altogether happy. But a more natural process is under way. 

The oak above has had more adventures than I can figure out. But one story this stump tells is that early in its life it was damaged and put up two trunks. Both grew separately for a few years and then fused together. Then they burned again and recovered again. The tree before cutting looked kind of miserable. But if there weren't so many others competing with it, it may have triumphed.

This hickory also had two trunks for a while, and a lot of challenges, including more burns and rot.

May it rest in peace.

This stump has another message. It has suffered ...

... some fire damage over the years, but the next fire could well obliterate it. A dead tree has fallen against it that could burn with a lot more intensity than a leaf fire. In the case of ancient trees of the most precious species (to biodiversity conservation), we stewards try to clear away such hazards before the controlled burns. 

This hickory stump was cut but not herbicided years ago. We thought that a more moderate approach. It's now rotting away, and out from it were growing two healthy new trunks. But bitternut hickory was probably not a substantial component of this bur oak woodland; there are way too many here. This time we'll herbicide them. 

The photo above shows yet another approach. Here, where bur oaks were damagingly close together, we girdled some. Girdling will kill them. Woodpeckers will appreciate those standing dead trees, as will the many insects that eat such dead trees, as will the bluebirds, great crested flycatchers, and flying squirrels that will raise their young in the holes the woodpeckers abandon. 

Once we thought we'd soon mostly just be "letting nature take its course." Now we find there's still more to it. 

Acknowledgements 

The stalwart Somme volunteers did the fine work that left these tell-tale stumps.

Thanks to Eriko Kojima for proofing and edits.