Fall Curtis Prairie
The grasses in seventy-five-year-old Curtis Prairie still reach skyward every autumn, but they can’t stretch tall enough to hide another worrisome trend. This grassland, the oldest restored prairie in the world, is slowly becoming a shrubland. A small mountain of willow now looms above the prairie’s eastern end, while grey dogwood — a native, but aggressive shrub — has grown almost as abundant as the prairie icon, big bluestem.
It’s a puzzling development for the Arboretum’s managers. Nearly from the start, they’ve set regular fires to burn off shrubs and other unwelcome plants.
Curtis Prairie is home, in fact, to some of the first experiments demonstrating the beneficial effects of fire. Seven decades later, however, fire doesn’t seem to be working anymore.
Paul Zedler, a UW-Madison environmental studies professor, Arboretum scientist, and Joy Zedler’s spouse, suspects that prescribed burns, which must be done for safety reasons during the cool, moist months of spring, don’t burn hot enough to kill shrub roots. Flows of nutrient-rich stormwater, the site’s legacy of farming — even global warming — could also be giving shrubs the edge. Or perhaps tall grass prairie always contained large patches of dogwood, sumac, and willow, Zedler muses, but settlers didn’t notice them as much when grasslands extended for hundreds of square miles instead of tens of acres. Whatever the explanation, Curtis Prairie is proving that, unlike a renovated painting preserved behind glass in a museum, “restored” nature is not so easily kept.
Few know this better than Steve Glass, longtime Arboretum land care manager. “The shrub invasion, of course, concerns us,” he says. “But in the face of climate change and the fact that ecosystems change anyway, we’ll have to keep learning and adapting. It’s how we advance restoration ecology.”