FRIENDS OF EDGEWOOD NATURAL PRESERVE

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RARE BUTTERFLY RETURNING TO EDGEWOOD

By Carolyn Strange

Photos by Ed Ross

Edgewood County Park and Natural Preserve is renowned for its spring wildflower displays, but the buzz in 2007 will be about what’s fluttering above the flowers, and munching below. Edgewood’s famous butterfly is coming home.

Neither big nor showy, the orange, black and white Bay checkerspot butterfly (Euphydryas editha bayensis) ranks among the most studied insects in science. Edgewood owes its status as a preserve to this butterfly, which federal officials listed as threatened with extinction in 1987. But legal protection didn’t stop an insidious chain of events that ultimately wiped it out at Edgewood, its last stand in San Mateo County. It was gone by 2003. The butterfly holds on at Coyote Ridge in Santa Clara County.

Backed by government agencies and advocacy groups, ecologist Stuart B. Weiss, Ph.D. sought to not only to understand the Edgewood extinction, but to also reverse it. "It's time for a win on the endangered species front," Weiss says.

But first he had to solve a mystery. Weiss found nonnative Italian ryegrass (Lolium multiflorum) taking over, crowding out native plants, including critical caterpillar food, California plantain (Plantago erecta). But soils derived from nutrient-poor serpentine rock (California’s State Rock) usually thwart nonnative plants, providing havens for natives. That’s why Edgewood dazzles with native wildflower carpets. What had changed?

Ryegrass encroached because soil chemistry shifted. Weiss has shown that vehicle emissions from nearby Highway 280 deposit nitrogen, essentially fertilizing the soil, and tipping the plant community balance. Weiss dubbed this disastrous freeway effect “drive-by extinction.”

Fortunately, well timed mowing effectively tips the balance back in favor of native plants. Now, nearly 15 acres host a homecoming. This winter Weiss has been transferring caterpillars from Coyote Ridge. By April, checkerspot butterflies will take wing again at Edgewood. Friends of Edgewood docents will share this exciting and hopeful story as part of weekend wildflower walks.

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