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Drought Threatens Major Ecosystem Shift on the Carrizo Plain

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Giant kangaroo rat | Photo: USFWS/George Harrison

It seems pretty much everyone in California is keeping their fingers crossed that the rainstorms approaching the state later this week will alleviate at least some of the drought's worst impacts. And according to one UC Berkeley ecologist, those impacts are hitting one of California's signature landscapes pretty hard, making those rains all the more important.

In wetter years, there's so much wildlife on the Carrizo Plain in San Luis Obispo County that observers sometimes call it "California's Serengeti." But a wildlife species that helps hold the whole ecosystem together is on the verge of blinking out of existence in this year's drought. If it goes, it could take the Carrizo Plain as we know it with it.

"Carrizo is already on the edge of converting to an entirely new system," Justin Brashares, associate professor of wildlife ecology and conservation at UC Berkeley, told Glen Martin in UCB's alumni publication California Magazine. "All of the values that make Carrizo so remarkable, the very reasons that so much energy, time and money that has been put into preserving it, would be lost."

The Carrizo Plain is already semiarid, so you might not expect the drought to be making as much of a difference there as it it's making in wetter places like Northern California's salmon streams. But this year is just one in a string of bad years for the Carrizo Plain's native grassland, Brashares tells Martin. Last year four fifths of the soil in the Carrizo Plain National Monument was bare, up from less than ten percent four years ago. This year's worse. And less grass means less food and cover for the giant kangaroo rat, the linchpin of the Carrizo Plain's ecosystem.

The Carrizo is no stranger to rare and imperiled wildlife, from the pronghorn and tule elk that have been reintroduced to the valley to the sandhill cranes that visit Soda Lake when rains fill it. But as Brashares tells it, it would be hard for a grassland to have a better ally than the giant kangaroo rat, Dipodomys ingens, a federally Endangered species. The giant k-rat eats exotic plant species, keeping the native vegetation intact. It digs burrows that are used by other animals, including the rat's companion on the endangered list, the blunt-nosed leopard lizard. The San Joaquin kit fox, another listed Endangered species that might be the most imperiled Californian mammal of all, finds a large proportion of its diet in the large rodents.

In other words, the k-rat functions as what ecologists often call a "keystone species." If the drought does in the giant kangaroo rat, the Carrizo loses all the ecosystem services it provides, and the grassland will likely unravel.

But aren't droughts like this year's part of the California landscape as well? If this is a 500-year drought, didn't the ancestors of the giant k-rats in the Carrizo weather it somehow? Martin answers that implied question succinctly yet eloquently:

Prior to Spanish colonization, the state was ecologically inviolate. There was plenty of room for various habitats, and the plants and animals that characterized them, to shift around. Back then, humanity existed in small redoubts encompassed by wilderness. Now the obverse is true. Our wildlands are islands surrounded by urban development or intensive agriculture. There is, in short, no place to move.

Despite almost 250,000 acres of the plain having been protected in the BLM-managed National Monument, says Brashares, the giant k-rat's habitat in the land beyond the Monument has been fragmented by solar development and agriculture. If the Plain's k-rat population gets pushed over the edge by the drought, there are no new recruits waiting in the surrounding mountains to repopulate the Carrizo.

All the more reason to cross those fingers.

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