Friday, October 30, 2015

A Fall Walk in the Tallgrass Savanna

A slender footpath threads its way through an Illinois wilderness – as the growing season ends – a time to relish the passing richness – and to think about what comes next.

Scarlet oaks stand out, and the bur oaks among them are nearly invisible. But burs have secrets worth knowing.

In the foreground, a young bur oak's craggy limbs, already leafless. Bur oak foliage is the first to fall. Why is that?
Perhaps because burs are the most fire-adapted of our trees.
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 it - except for its weapon of fire. Raging fire is how burs clear the competition – young invading trees that would shade out and replace them. The sooner the leaves fall, the more chance bur oaks can employ their leaves' crisp, stored fire energy to burn the sap out of their competition. 

Indian hemp grows among the oaks.
The Potawatomi didn't smoke it. They used the fibers to make string and rope for their needs. We who love the savanna
are learning to re-inhabit and care for an ecosystem that has had people as a part as long as it's been here. 

Not only trees, grasses, and wildflowers - shrubs may be more key to the savanna than to any other ecosystem.
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, and for our soul.

In prairies, New England aster is seen as kind of a weakling, typical of young restorations, 
dropping out as the community matures.

But a curious thing happens on the way to the savanna. This shrub is 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 too, and it starts over.
Plants adapted to disturbance, like New England aster (leaves at lower left, 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 of a partly-burned-off nannyberry shrub.
Probably all the grasses, sedges, and flowers here have some 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 are 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
(and of course by the 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 oaks that surround it.
Scarlet oak, like hazel, has thin bark and under a natural fire regime is 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 the stewards are spreading 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.
Since most of the old oaks have met premature death, because of wounds suffered during nearly two centuries of invasive pressures, we wonder if we should rake around this one to keep in from burning up.
Sometimes we do it. Sometimes we don't. So far it survives. We're not sure what's best. 
This grand old wreck of a tree stands by itself,
framing views of dramatic scarlet oaks and hidden young burs in the distance. 
Nearby lichens, mosses, fungi, and animals are gradually turning the trunk of a fallen old giant back to soil and air. 

We remember when it fell. It was precious to us as a tree, and now it's precious as a log. We're glad it finally had a chance to reproduce, and we rejoice in its many saplings nearby. These organisms are our friends. As we learn and understand more and more about them, we enjoy being better neighbors. It's a good feeling to walk through all this thriving natural richness, season by season.