From Little Acorns

There’s at least some good news from El Nino’s drenching rains. And it’s plainly evident all over the rolling hills and fields of Sedgwick Ranch, in the lush Santa Ynez Valley 35 miles north of Santa Barbara.

Thanks to the downpours, for the first time in years, acorns are sprouting by the hundreds on the 6,000-acre-spread, a seemingly happy reaffirmation of the old saw about little acorns yielding mighty oaks.

“I can hardly keep count of all the seedlings,” said Claudia Tyler, a UC Santa Barbara ecologist who planted the oaks with student volunteers last fall to help solve a nagging scientific puzzle: Why aren’t these icon trees of the California landscape reproducing without human help?

Still, while delighted with her crop, she can’t proclaim an arboreal bonanza--yet. Before her 3- to 6-inch seedlings become full-fledged oaks, in a decade or more, they must overcome a host of hurdles--the summer’s heat, inevitable drought, grazing cattle and many predators. “But,” she added, “it’s a start.”

It’s a crucial start for a threatened part of the state’s natural heritage--what biologists call a “signature” species giving a place its special feel. For some time now, oaks have been in trouble--and not just on bucolic Sedgwick Ranch, which recently became part of the UC Natural Reserve System--a collection of about two dozen unspoiled areas scattered across the state. The crisis exists in the 48 California counties in which oaks are found.

For more than a century, oaks have been relentlessly chopped down for fuel, farmland and urban expansion. “We’ve really done a number on our oak resources,” said Rosi Dagit, a conservation biologist for the Reserve Conservation District of the Santa Monica Mountains who has been trying to help communities restore some of the oaks that once dotted the Los Angeles area.

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Indeed, the oaks’ plight appears to be worsening. In the last 15 years, about 300,000 acres of oak woodland have been lost, according to a new study from the U.S. Forestry Service.

A major reason is the explosive growth of California’s wine industry. It is turning wooded hillsides into vineyards at an accelerating pace, not only in traditional grape-growing northern counties like Sonoma but also on the Central Coast.

Last fall the Kendall-Jackson Co. bulldozed 843 ancient oaks on nearby ranchland to make way for its new Camelot Vineyard--and touched off a local furor among oak lovers.

But California’s oaks are also endangered by a more subtle--and ultimately more serious--threat. Even in places where they have been protected from chain saws or bulldozers, as on Sedgwick Ranch, the trees are not reproducing.

Comparing recent aerial photographs of the property with photos dating back to the 1940s, the UC Santa Barbara scientists found that the ranch’s oak population had declined by nearly 20%--even though the late sportsman-sculptor Frank Sedgwick, who bequeathed the ranch to the school, allowed only occasional cutting. Worse, many of the trees, especially the majestic valley oaks--which grow as high as 75 feet and live for three or four centuries--turned out to be mostly old and gnarled, near the end of their lives.

“There’s simply no replacement for trees that are dying,” said geographer Frank E. Davis. Similar declines have been observed elsewhere in the state. In several cases, harmful fungi appeared to be killing coast live oaks. But lack of regeneration of oaks on ranch lands is another matter.

The chief culprits have always been thought to be cattle. As they graze, they often trample budding acorns, eat seedlings and browse on leaves of larger saplings (trees about 6 feet high). Even so, something else must be afoot, because poor oak regrowth seems to continue even after cattle are removed.

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That baffles scientists. A mature tree typically produces hundreds of acorns, shedding them in the first autumn rains. “Only one [acorn] has to succeed every century or so for a tree to reproduce itself,” said botanist Bruce E. Mahall. “Why isn’t that happening?”

In part, it’s because acorns face steep odds. Even if they aren’t crushed by cows, they are likely to be gobbled up by ground hogs, wild pigs, squirrels and other rodents, or birds, though scrub jays, acorn woodpeckers and western gray squirrels often accidentally help oaks propagate by forgetting to collect acorns they’ve stashed in “granary” trees or in the ground. Later, as seedlings and saplings, surviving plants run other hazards: for example, the voracious appetites of smaller browsers such as rabbits and grasshoppers, not to mention cattle and deer.

So how did acorns manage to make it in the past? Biologists believe the environment may once have been more favorable to oaks. Before large-scale ranching, seedlings didn’t have to compete for sunlight and water with aggressive exotic grasses that have been imported for cattle grazing. Also, populations of ground squirrels, gophers and other acorn-eaters were kept in check by natural enemies such as hawks, eagles, bobcats and mountain lions.

“Predator populations probably still haven’t recovered from the days when people shot everything in sight,” Mahall said. Other factors that could have helped oaks: higher water tables, more favorable rainfall patterns and better soil conditions, allowing the beneficial fungi and bacteria on which their roots depend to flourish.

To get some answers, Davis and Mahall began their experiment in planting oaks. As field manager, Tyler laid out 52 study sites across the ranch on different types of terrain. Each site was about half the size of a football field and had a mature oak on it.

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To provide controls, the sites were set up in adjoining pairs, with one left open to the cattle that Cal Poly San Luis Obispo runs on the ranch, the other closed off by electric fences. In some places, the acorns were entirely unprotected, marked only by a steel plate to help Tyler find the spot with a metal detector. Elsewhere, they were enclosed in mesh cylinders that shielded them from rodents, birds and other acorn-eating animals, as well as burrowing animals such as gophers and wild pigs.

When the tedious job was finished, the researchers waited out the winter’s heavy rains to see what would happen. To Tyler’s astonishment, when she began surveying the sites a few weeks ago, she found nearly half of the acorns had germinated into seedlings. Even more surprising, success was almost as great (30%) for unprotected acorns as for those protected from cows (30%-40%) and small predators (60%-80%). “Apart from predation by the likes of gophers, it seems clear the level of rainfall was the key--at least with this year’s crop of acorns,” she said.

Even so, the results are only a start. “We have to see whether the seedlings survive the summer months, when rainfall is likely to be scarce and the lush spring grasses begin to wither and dry. Then cows and other browsing creatures may turn to the leafy little oak seedlings for a snack,” Tyler said.

She and her colleagues know they won’t solve the riddles of oak regeneration soon. The trees grow much too slowly for quick answers--a valley oak, for instance, may stand only a few feet tall even after 10 years.

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But the scientists are willing to wait--if it helps the oak survive. As a “keystone” species, oaks provide habitat and sustenance to countless other life forms. “Without oaks you would lose some 5,000 different kinds of insects, 58 species of reptiles and amphibians, 158 birds and 105 mammals,” Dagit said.

Even dead trees offer nesting sites for woodpeckers and other birds. Oaks are also vital to our own well-being. With their long, sinuous roots, they stabilize slopes, reduce runoff during floods and protect the level and purity of the water table.

“We’re just beginning to appreciate their importance to the ecosystem,” said Janet Cobb, executive officer of the California Oak Foundation, whose 10-year-old organization recently persuaded the Legislature to declare the first Friday of November as Native Oak Day. “We’re finally beginning to persuade people it’s not a weed tree.”