Fall on the savanna.

We’re not New England. No one rides by in buses to check out the pastel colors of the leaves.

But, in person, to someone with a feel for it, our natural ecosystems are:

Rich, beautiful, subtle, meaningful, deep.

 

We walk slowly, notice patterns that develop, and hypothesize about what’s causing them. (In some cases, we take actual data to prove or disprove.) 

 

It’s fun to watch – like a novel or a movie – but one where the plot develops over years. Like watching the course of a human life or a social movement. In this case, life is good. 

This is a patch of "shrub prairie" - one component of the savanna. 

Here the shrub in the foreground is hazel (the plant that makes hazelnuts), and most of the rest are bur or Hill's oaks, both species that often burn off in fire and become shrubs.

This photo reminds us how central regular fires are.

The one leafy tree and many leafy shrubs are all Hill's oaks (also called scarlet oak).

The bare young tree with heavy branches (on the left) is the bur oak.

Bur oak runs the tallgrass savanna. It's the first tree to drop its leaves, perhaps as a fuel weapon against the other trees. Heavy bark protects it. Fires of grass and oak leaves burn off its woody competition. In time, all the Hill's will be shrubs, and the bur will be a mighty tree. 

The hazel too is quick to burn off.

In this photo you see last year's naked dead stems, much taller than this year's leafy ones.

If it now doesn't burn here for a year or two, those three-foot live stems will be six feet, or nine.

Then they'll produce lots of delicious nuts.

But the hazel's bank account is in its roots. It expects to burn. Without burns, trees would shade it out; its home is the frequently burned savanna and open oak woodland. 

In October and November, the waning of life pulls on our heart strings. 

Beautiful, partly painful, a kind of death, and a feature of our temperate climate. 

Big dry leaves here are prairie dock. Peachy are the leaves of rigid goldenrod. Red-wine-colored are the leaves of azure aster. Pale yellow for the moment is northern dropseed grass. Tawny is little bluestem. Most of these colors will drain out as winter sets in - unless all turns deep black from fire.

Kinds of diversity.

There is diversity within species: 

For example, some of these dropseed clumps are still green, some yellow, some already winter tan. 

And there is diversity between species: 

The early goldenrod leaves, despite this being the first goldenrod to bloom, are now still green (upper left), photosynthesizing full blast and taking advantage of their preferred cooler weather. The purple here is gray dogwood. Notice at least two small Hill's oaks as well. The dogwood and Hill's will outcompete the herbs in years between fire ... then get knocked back into dynamic equilibrium. 

If this site were burned every year, sometimes in the summer even, might the woodies go and the ecosystem gradually become all herbs - a prairie?

Above is another competition.

The tall grass here is cordgrass. The tall woodies are Hill's oaks. 

But the little green/yellow bur oak in the foreground will likely be the actual tree here in time. 

And the fine leaves of dropseed grass likely will replace the cord grass, which spread here from a nearby wetland while the slow-growing dropseed was getting bigger with every burn in this dry-ish spot. 

We'll watch. 

Stripes and patterns form.

The stripes in the middle distance follow contours. 

Species win out where the hydrology, soils, and fire regime are just right for them.

Here the front stripe is willow aster -

a brocade of subtle colors where a month ago all was green.

The black stripe behind it is woodland sunflower. 

Why do some species just turn black?

Behind that is a stripe of mostly white oaks, not native here, planted here long ago on former prairie.

In some areas, the fires have been knocking off the white oaks, killing them dead.

They're not like Hill's. 

In the space between these two stands of planted white oaks, we see original open prairie in the distance.

This savanna stood on the edge of the prairie. 

The seventy-acre Somme Prairie immediately to the west is being rapidly and profoundly restored. 

In the future, healthy tallgrass savanna and prairie will connect here, a rare thing ...

... also potentially important for some species that use both habitats.

Once such species, the rusty-patch bumblebee, has been found here. 

Here we see bur oaks, the true, original, natural tree here, a little further up the slope.

The oldest of these burs have heavy, spreading lower limbs, indicating that they grew as young trees in the open. Some are old enough to have been walked beneath by Potowatami, bison, bears, and the first Euro-American explorers. When natural fires stopped, subsequent young trees grew thin, straight, and tall. Removing the buckthorn was good, and now we also remove too dense pole trees, often of species native to the region but not to this ecosystem, or even too-close-together bur oaks, that today's weaker fires can't thin. We plan and study. No bur oaks reproduce in shade this dark. This former savanna may need to have fewer, shorter, wider-spreading trees to be all it can be, for biodiversity and a thriving future. 

At the other end of the shade continuum is this larger patch of "shrub prairie." 

Here, hundreds of bur and Hill's oaks and hazels burn back to square one with every fire.

Finally, a last photo of today, October 22, 2020.

More of a characteristic savanna,

scattered trees amid warm-season grasses.

In coming months, rich Fall color will turn to the sere of Winter ...

as we and other animals and plants prepare for

 another growing season of richness and drama.

Acknowledgements

Thanks to Christos Economou and Eriko Kojima for many helpful edits. 

Thanks to Cook County Forest Preserves staff for excellent burns in recent years. They make the difference.