A Fall Walk in the Tallgrass Savanna

The slender footpath threads its way through an Illinois wilderness. In deep, rich colors, this growing season heads toward its end. We relish memories of the growing season – and think about what comes next.

Scarlet oaks stand out, and the bur oaks among them are nearly invisible. There's a reason for that.

In the foreground, a young bur oak's craggy limbs are already leafless. Bur oak foliage is the first to fall. Why? Perhaps because burs are the most fire-adapted of our trees. Fallen leaves are their weapons.
Thick-barked bur oaks live on the edge of woodland and savanna – nearest the fire-prone prairie. Burs can’t survive in the shade of any other tree. All other species can outcompete them in the shade - except for its weapon of fire. Through raging fire, bur oaks clear the young invading trees that would shade out and replace them. The sooner the leaves fall, the more chance their crisp, stored fire energy can burn the sap out of their competitors. 

Indian hemp grows among the oaks.
The Potawatomi didn't smoke it. They used the fibers to make string and rope. And they burned to keep such resources coming. This plant is a big supporter of now-rare pollinators at a crucial time. We who love the savanna are learning to re-inhabit and care for an ecosystem that has had people as a native part as long as it's been here. 

Not only trees, grasses, and wildflowers - shrubs characterize some savannas.
This one is arrow-wood viburnum. Deer eat shrubs. Arrows kill deer. People maintained the savanna in part because it was so rich in the food, medicine, and other materials that they needed. Our society today needs it for genes to benefit medicine and science, for ecosystem services, for generosity to the planet, and because its richness and beauty make our souls happy.

In prairies, New England aster is seen as kind of a weakling, typical of young restorations, 

dropping out as the community stabilizes. But savannas have trees that stir the ecosystem - growing larger and later dying. They never get as stable as a prairie. This aster fits well here.

Another non-stabilizer is this shrub - hazelnut. As with bur oak, its leaves fall early
and burn hot. But without bur's armored stem, the above-ground parts of the hazel burn off too. After every fire, its hearty roots send up new stems, and it starts over.
Plants adapted to disturbance, like New England aster (you can see its now green-red leaves below the hazel, above) find their niche for a year or two, until the shrub grows back. 

The fringed gentian is a much rarer and more conservative plant than New England aster.
But it too seems to appreciate disturbance.

Here the gentians are just a couple of blue dots in the background behind a partly-burned-off nannyberry shrub.

Probably the grasses, sedges, and flowers here have many adaptations to their dynamic fire-pruned shrub neighbors.   

Briars are beautiful, delicious, and under-appreciated members of the shrub club.
This one is black raspberry, identifiable by its powder-blue canes. 

Many species of roses also support shrubland wildlife. Tangles full of roses are especially appreciated by birds for sequestering their nests. This one, with most leaves in fives, is swamp rose. 

And here, most leaves in threes, is Illinois rose, one of the biggest, sometimes climbing ten or fifteen feet up through the shrubs and saplings. Its hips (fruits full of seed) are eagerly sought by Shrub Club restoration teams (for planting) and of course by animals (that eat them). 

But in the savanna, the oak dynamic is key. Here a lone bur oak (no leaves, center) - with its thick, corky bark - can be expected to outlast and replace the scarlet or Hill's oaks that surround it.
Scarlet oak, like hazel, has thin bark and under a natural fire regime it's mostly a shrubby "re-sprout tree."

In many areas of Somme Prairie Grove, most of the trees are the "upstart" scarlet oaks.
They invade former pastures quicker than burs because their small acorns are spread far and wide by blue jays. Most survive our relatively-mild controlled burns for many years, but bit by bit they seem to be replaced by burs. Squirrels rarely venture out here, so hard-working stewards play squirrel and spread the fat bur oak acorns. 

Gradually some savannas become bur oak groves, very resistant to fire.
But oaks may live three or four hundred years; some here predate the coming of the Europeans. They are our elders.

Vestal Grove's biggest oak is this giant, now with a fire-scarred hollow trunk.
We rake around it before fires, to keep it from burning up too soon, so its acorns with their ancient genes will continue to rain down, as this ecosystem recovers.  

This grand old wreck of a tree stands by itself, limbs resting on the ground. Fire would most likely have burned them off in the natural landscape.  

Nearby lichens, mosses, fungi, and animals are gradually turning the trunk of a fallen old giant back to soil and air. 

This old giant had been precious to us as a tree. Now it's precious as a life-filled log. It has many saplings nearby. These organisms are our friends. As we learn and understand more about these organisms, large and small, we enjoy being better neighbors. It's a good feeling to walk through all this thriving and changing natural richness, season after season.