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If You Mow It, They Will Come

Stu Weiss and I are strolling at Edgewood Park and Preserve, a bucolic swath of greenery just south of San Francisco in San Mateo County, California. Here, Weiss and his fellow scientists from the Creekside Center for Earth Observation aid and abet the citizenry in helping to resuscitate populations of the Bay Checkerspot Butterfly and the San Mateo Thornmint, both endangered species. Weiss’s team has laid out a transect in which they are counting up thornmint stalks. Their focus on the sparse plants is so close, they look like surgeons at a green operating table.

Weiss and I walk over to a hillside facing Interstate 280, the very road by which I had travelled to meet him. Cars wing endlessly past. I used to commute along what some call the most beautiful highway in America, with the Santa Cruz Mountains on the one side and the golden hills on the other. But listening to Weiss tell me about his work here, I realize I have never quite seen this place before.

Weiss points out that behind us the hillside getting full sun “could be Southern California.” There is a tangle of chaparral, sage, chemise and deer wood. Beyond the highway, the mountains are full of oak woodlands and Doug fir. It’s a different microclimate over there. Weiss points out a small smudge of lighter vegetation in the dark green tangles. “There’s a stand of chaparral,” he says. “Ready to take off.”

What I might describe as ample purview for a traditional California landscape painting Weiss sees perhaps as Seurat or Van Gogh would have done. One pretty scene to me is to Weiss a mosaic of geology, vegetation type, aspect in relation to the sun and rainfall, and atmosphere – not only full of too much CO2 but thanks to the steadily streaming cars, too much nitrogen.

And not only does Weiss see the invisible gases, he sees into the future. Weiss and other scientists studying what global change is doing to biodiversity wrangle over the concept of “climate space.” When he says the chaparral are ready to take off, he means that as temperatures rise and the landscape gets drier, much of the mixed hardwood forests we are looking at could disappear, and plants like chaparral could take over. Microclimates result from a myriad of inputs, and these are being reshuffled. The future will be a different picture altogether.

Weiss reminds me that the highway is built along the San Andreas fault line, the result of the two converging tectonic plates, the Farallon and the North American. Some of the resulting rocks from the mash-up of the plates between 35 and 165 million years ago are serpentine – California’s official state rock. Serpentine is why we are standing here. Nutrient-poor, the limitations of serpentine soil have created a refugia for endemic plants and animals, including Plantago erecta, upon which the Bay Checkerspot depends.

The trouble for the Bay Checkerspot right here is the traffic. Nitrogen in the cars’ exhaust actually fertilizes the soil, making it hospitable to the invasive Italian rye grass that grows up higher than the Plantago erecta. Eventually the grass thatches over and suffocates the natives beneath. The butterfly can’t get to its favorite food and perishes.

Oh the world and our woes! But there is a solution, here, and Weiss figured it out. “Grazing and mowing,” he says, simply. In other beleaguered Bay Checkerspot habitat Weiss has successfully argued for cattle grazing to keep the rye grass low enough that the native flowers can get some space. This piece of habitat is too small for cattle so the county mows it once a year. “It’s really like gardening,” says Weiss. “You have to take care of each piece of land.” And then the butterflies will come.

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