Wednesday, May 16, 2012

White oak -- the living dead?

White oak is still a common tree. But less and less. It doesn’t seem to do so well in parks and lawns, and in the forest, while 200 and 300-year-old trees may be frequent, in most woods the young white oaks nearby add up to zero. They’re not reproducing, except in temporary situations.

Oaks need fire. Bur and scarlet oak thrive on prairie and savanna fire. White oak does not. Consider the ones planted at Somme Prairie Grove “by mistake.” Decades ago, long before the science of ecology had learned much, foresters trying to restore forest planted white oaks here with birch and silver poplar and other questionable companions.   Now white oaks here are starting to look like the one below.

A controlled burn last fall killed the lower branches, although you couldn’t tell that until spring when the live branches leafed out.

The fires here may be very good for Leiberg’s panic grasses, great spangled fritillary butterflies, smooth green snakes, orchard orioles and hundreds of other fire-dependent species of the oak savanna. But the white oaks are on the retreat. They’ll gradually give way to nearby bur and scarlet oak, wild plum, hazelnut, and other savanna shrubs, trees, grasses and wildflowers.

You see the future starkly in another part of the same preserve.

Two beautiful white oaks standing just northeast of tall grass (that is, dense fuel) were killed outright by a fire years earlier. On one level, it seems a tragedy that these fine old trees died, but on a more profound level, the important thing that’s happening here is that a rare ecosystem, supporting thousands of rare species, is coming back into sustainable balance. White oak is apparently just not part of the long-term healthy savanna – at least in this part of this preserve.

Where will such a noble tree thrive? Not in the unburned forests, where it can’t reproduce in the shade. Not in people’s yards, where landscapers recommended other species better adapted to lawns.

Perhaps in the open oak woodland, another rare and poorly understood community. Here the fires are not as hot; there’s less grass in the dappled shade. Often there’s a more rugged, fire-disrupting topography. Open oak woodlands have their own specialized, beautiful communities of birds, mushrooms, butterflies, wildflowers, ants, walking sticks, nematodes, bacteria and biodiversity heritage generally). 

We still don’t know what it would take to restore full health and a secure future to this important part of our planet. It will be fun to find the answers. And it will take at least decades, so let’s do it while the ancient white oaks we have left still have life.

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