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Cattle grazing aids seasonal wetlands
Destruction seen as only way to preserve the last vestiges of vernal pools ringing the bay
FREMONT -- Cattle started trampling some of the rarest, most sensitive wetlands abutting San Francisco Bay on Monday, ripping up grass and scattering hoof prints and cow pies across the landscape.
The destruction brought nothing but smiles to the faces of federal wildlife biologists looking on, because it's the only way managers at the Don Edwards San Francisco Bay National Wildlife Refuge know to preserve and restore their fragile vernal pools.
"This is our biggest opportunity," refuge manager Clyde Morris said as 17 Black Angus cows and two calves scurried free of the holding pen. "Every other seasonal wetland or upland (ringing the bay) has been developed."
Vernal pools, once ubiquitous in the Central Valley and around San Francisco Bay, are little pockets of land that fill with water in the winter, slowly evaporate in the spring, and spend summer and fall as dry as a piece of stale toast.
The unique ponds offer shelter for a variety of rare and endangered species: tadpole shrimp, which hatch, grow, reproduce and die inside of two months; Contra Costa goldfields, a bright-yellow flower found only in four California counties; and the California tiger salamander, which spends summer lying dormant underground.
And while most vernal pools in California have succumbed to either the developer's spade or the farmer's blade, these at the refuge face a different threat -- non-native grasses and weeds, which alter the landscape and snuff out the pools' ability to hold water.
That's where the cows come in.
Cattle knock back the weeds, reducing thatch, opening up the landscape not just for the shrimp and salamanders and flowers but also burrowing owls and other creatures.
"Grazing seems to be the best long-term plan with impacts desirable for this habitat," said Sally Reynolds, a botanist with the refuge's Warm Springs seasonal wetlands unit. "While the pools are full and the grass is growing is when we want to hit'em with the cows."
Refuge managers will start slowly, grazing less than 20 pairs of cows and calves on 105 acres for about six weeks. They hope to graze 40 or 50 pairs over a larger area in the spring and fall and compare grazed sections with ungrazed control plots for at least three years.
Reynolds and others say the outcome shouldn't be a surprise. Cattle had grazed the 255-acre parcel for at least a century until the federal government bought it in 1992 and kicked the animals off. Since then federal biologists have seen a steady decline in the size and quality of the land's vernal pools.
"The impacts of removal are visible pretty quickly," said Sheila Barry, a natural resources and livestock adviser for the University of California Cooperative Extension.
Once brush and nonnative grasses and thistles get established, she added, "it's real hard to go back."
The refuge has tried spraying herbicide on thistle and pulling batches of pepperweed by hand. If grazing doesn't work, Reynolds said, the only other recourse is fire.
But a short, unpredictable burn season and dense development surrounding the refuge means maybe 20 acres could be burned every two years, Reynolds said.
The unorthodox decision to graze has brought approval even from those who oppose grazing on public lands. They like the management plan's comprehensive scope and plentiful controls but fear the cattle could trample the very landscape they're supposed to save.
Years of study on vernal pools elsewhere have Barry and Reynolds convinced the cattle can only help.
Said Reynolds: "We've realized the habitat needed to be more closely managed."
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