Tutored by the Snow - early winter 2025

November 29

Yesterday some fringed gentians were still blooming. Today, nothing distracts from the stark skeleton of the savanna ecosystem. Shorter-term thinking subsides. Underlying structures come to the fore.

First trees. Then animals. 

This young bur oak is an ongoing triumph. A farmer has cut the trees here, understandably, to make a short-lived cornfield. Then we went to work to restore the millenia-old savanna that still thrived in pockets here and there. Restoration of grasses, wildflowers, and many animal species is relatively speedy. 

But for decades we had no sapling oaks. Instead, what we had were oak bushes. In the photo above, there are at least ten visible. Oak reproduction suffered from two challenges. First, the necessarily frequent fires top-killed them, so after each fire they had to start over. Then, the deer ate the fresh shoots back so often, that for decades none got taller than a foot or two before they'd get burned back again. New plan: This one we protected from both fire and deer. It's on the way to playing the needed role of a savanna tree. 

The two closest oaks have immense limbs that stretch west. Surveys confirm that these trees mark the former line between prairie and oak savanna. To the west (left) was treeless prairie - tall grass and bison - to the horizon. To the east, bur oak savanna with deer and mountain lions.

These two trees probably date back to the early years of Euro-american settlement. The long, low limbs would not have survived the prairie fires coming from the west when this was Potawatomi land. They're an awesome and eery inheritance.  

But in the former cornfields, it's not obvious how to make oak management decisions. All the bushes and trees here still holding their brown leaves are Hill's oaks. They're the ones that reproduced when the corn field became a Forest Preserve. 

But bur oaks are the key tree species of the savanna that was with its thousands of interdependent animal and plant species. With fire, they're now coming back, by the hundreds in some areas. How many does the ecosystem want? If we let all the trees here grow, they'd shade out and kill off the understory of rare grasses and wildflowers - along with the rare animal species that depend on them. In the long run, we now believe we want structural diversity. In some areas, the fires are gradually top-killing all the tree species except the bur oaks. We see our challenge this way: let enough of them get sufficiently big to survive the fires most of the time, and then let the fires decide the rest. 

Thus, in areas of few burs, they now look like this: a cage protects from the deer, and a blue-and-white flag reminds us that this is an area where we'll first rake excess fuel away and later, during the controlled burn, set a back-fire downwind of it to reduce the intensity of nearby flames. We'll do this each year this area burns until this tree gets big enough to survive on its own. 

In some areas, with ten or twenty young burs, where there's only space for one big tree, we've stopped protecting them altogether.

But much of the site has none. So here, if you look close, you'll see a scrawny young tree protected from deer with a cage and from fire by a circle of fuel cut and raked away. Once again, if we didn't also back-burn, the thirty foot flames of a head-fire would top kill this youngster anyway. 

Animals also deserve some mention.

They're not immediately obvious today. In the photo below a deer blends with the grass and oak leaves. 

We don't see the white-footed mice, but they leave holes where they seem to come to the surface to take a look or breathe fresh air. Mice and meadow voles are under snow and grass thatch. But they're here by the thousands. 

For most of this walk, I don't see a single bird. I know there are woodpeckers, nuthatches, and chickadees back in the trees, but I'm mostly in the open. I don't see them, but most everywhere I see the scene below:

Scrub sparrows are feeding on the seeds of the tall grasses ... and leaving wing-marks on the snow. 

During the breeding season, when I monitor the birds, I find about forty individuals of about twenty species, spread everywhere. Today in he snow I finally come across the forty birds that live here in the winter. They're all one species and all in one flock. 

The poorly named "American tree sparrow" spends its summers on the arctic tundra and taiga ... and its winters among the grasses. It's a pleasure to watch their "popcorn" feeding behavior, as shown here. 

There were a lot more winter birds here before we cut the buckthorns. The birds that relish their berries are gone now. They were mostly robins but also some bluebirds and cedar waxwings. Our progress on restoring berry-bearing savanna shrubs has been slow. Something else to think about on winter days. But they're also beautiful, so this post will end with a sunset.

For a Somme snow animal tracks post by Rebeccah Hartz, click here. 

For a reminder of how this area looked in July, click here. 

Thanks to Eriko Kojima for helpful edits and proofing.

Thanks to All About Birds for the tree sparrow photo.