In 1974, growing plums was still a viable means of making a living in Sonoma County, but farmer Lou Preston foresaw a better way to harvest an income. So he pulled out his 200 acres of prune trees from his family's Dry Creek Valley property and replanted the acreage with wine grapes. Preston was ahead of the times, doing what hundreds of other landowners would do 10 and 20 years later as California's wine industry exploded. By 1980, Sonoma County's prune industry was essentially gone. Olives and walnuts were also on the way out, and the county's apple orchards were shrinking.

And vineyards took over. Today, Sonoma County is planted with 56,522 acres of wine grapes, according to Sonoma County's 2010 crop report—up from about 12,000 acres in 1970. Other crops, including walnuts and prunes, have virtually vanished from the region (in 2010, there were just 79 acres of walnuts in Sonoma County, and 39 acres of prunes), and wine grapes now make up more than 90 percent of the cultivated land in both Sonoma and Napa counties. Though prices of grapes have fallen some in the past several years, farmers still have a huge incentive to keep growing grapes; at about $2,000 per ton on average, local wine grapes are by far the region's most valuable crop.

But Preston, who founded Preston Winery in 1981, has taken a dramatic—and voluntary—step backward. Though he and his family helped spark the region's vineyard explosion, they are now converting their property into a diverse farm, and to do it they've removed 40 percent of their moneymaking vines and replanted the acreage with fruit trees and vegetables.

For Preston, the change came when he started farming organically about a decade ago. In doing so, he says he simply became cognizant of better ways to manage the land. He saw the sustainability issues in monocropping, especially in using petroleum-based fertilizers to replenish the soil every season and in using poisons to kill insect pests.

"We began to wonder whether we ought to be a monoculture," he says. "It's not good for the land, and it's not good for the ecosystem."

Preston now grows 50 acres of peaches, walnuts, olives, pineapple guavas and many annual fruit and vegetable crops among his grapevines. He also has grazing animals and chickens roaming the farm. Fruits and vegetables are sold at a produce stand outside the tasting room, while some of his harvest goes to farmers markets and another portion goes to area restaurants.

Wine sales still pay the bills, Preston says, and quantifying the virtues of his business model is difficult. Preston says that "the land seemed to respond positively" to the diversity of crops after he began converting his vineyards. For one thing, the diversity of plants now hosts insect populations, which keep each other in balance, and he says that significant pest outbreaks haven't occurred since he diversified his farm. "It feels right," he says. "It seems like a perfectly natural way to manage land."

For Kevin McEnnis, co-owner of Quetzal Farm in Santa Rosa, crop diversity provides security against harvest failure of one crop or another. His eggplant crop, for example, failed last year due to cool weather, but his dozen other crops did not. "If we'd been an eggplant monocrop, we'd have needed crop insurance," he says.

At Orchard Farms in Sebastopol, owner Ken Orchard says this spring produced his first good spinach crop in six years. "If I'd been depending on spinach alone," he says, "I wouldn't have done well." Orchard, who farms organically, also says his wide array of about 50 fruits and vegetables attracts shoppers at local farmers markets in Sebastopol, Santa Rosa and San Rafael.

But on the macro market, the forces of economics pull in a different direction and have drawn much of the world into a system of monoculture. The grain fields of the Great Plains are a monoculture. So is the almond industry of the Central Valley. Citrus groves in Florida, banana farms in Ecuador, olive orchards in Spain, coffee plantations throughout the tropics and alfalfa fields in Southern California's Imperial Valley also amount to monoculture.

As do the North Bay's grids of grapevines.

"A monoculture is a factory model," explains Frederique Lavoipierre, coordinator for the entomology outreach program at Sonoma State University and the manager of the school's organic garden program. Monocultures, she says, allow for a streamlined industrial use of the land, which can be planted, sprayed or harvested all at once, with the crop sent en masse to local processing plants. "There are obvious cost benefits to farming that way in the short term," she explains, "but we know it's not sustainable."

Soil quality suffers, for one thing. In diversely planted areas or in those where crop rotation occurs, essential soil nutrients can be maintained naturally in the soil via photosynthetic processes. In most large-scale farming scenarios, though, heavy use of petroleum-based fertilizers is the norm. These, in turn, can have negative impacts on a region's ecology. So-called oceanic dead zones, like the sterile region in the Gulf of Mexico, result when fertilizers washed to sea via rivers cause algal blooms that in turn use all the oxygen in the water, depriving other organisms of life.

Monocultures also render croplands vulnerable to massive pest outbreaks—the answer to which is the use of pesticides and fungicides. Honeybees, too, may starve if left to live in a monocropped region, where nectar flows occur only several weeks of the year.

Still, it isn't feasible to grow everything in small, multicropped plantations. As McEnnis says, "Small-scale wheat is really neat, but, boy is it expensive. So we may need monoculture farming at some level."

Ted Lemon calls petroleum dependency and chemical contamination "the hidden costs" of maintaining the modern agricultural model. Lemon and his wife, Heidi, own and operate Littorai Wines west of Sebastopol. Lemon farmed conventionally for about 15 years before, as he says, he "became frustrated with the Western agronomic model, which is essentially based on mineral fertilizers." He tuned in to the practices of biodynamic farming, and today, the Littorai vineyards are surrounded by companion plants, hay and woodland, with animals grazing over certain quarters.

Monocultures may come in varying sizes, and Lavoipierre notes that defining a monoculture is a tricky matter.

"At what point do you call something a monoculture?" she asks. "Is it 10 square feet or a hundred square feet or an acre or a hundred acres? I would say that something isn't a monoculture until we begin seeing negative impacts."

In the North Bay, we may have passed that point. According to Lavoipierre, problems associated with Pierce's disease, devastating for grapevines, could have been largely averted had more grape growers left vacant buffer zones between their vines and riparian stream zones, where the bacteria's vector insect naturally lives.

Beekeepers also say that monocultures have negative effects on bee populations and are perhaps even a major cause of the much-discussed phenomenon of colony collapse disorder, or CCD, which has seen the decline in numbers of bees worldwide. Healthy bee populations, so essential to many food crops, depend on landscapes that are botanically diverse, producing flower blooms year- round.

"Vineyards are basically starvation zones where the bees can't get any food," says Liz Russell, a beekeeper in Forestville. She and her husband, Joey Romo, have found it increasingly difficult to maintain their bee colonies and have had to move their hives twice in the past four years, in each case because a small, multicropped organic farm was converted into a vineyard.

Rob Keller, a beekeeper in Napa, says farmland, especially of the monoculture sort, makes notoriously poor habitat for bees, while urban areas provide the diversity of flowering plants that can keep bees fed all year. The problem with this counterintuitive paradigm is that urban gardens and greenways occupy just a small portion of the overall land area, severely limiting the regions in which bees can thrive.

"Basically, the further out of the urban area you go, the harder it is to be a bee," says Keller, who recently watched female worker bees forcibly eject male drones from several hives he was keeping among some vineyards, a sure sign, he explains, that a bee colony is short of food.

Keller says two acres of fallow, wild land for every 10 acres cultivated would provide plenty of food for bees. He says the Napa Valley Reserve in St. Helena is a rare example of a bee-friendly vineyard. Here, buckwheat and safflower, hundreds of fruit trees and vegetable plots grow between the grapevines. The vineyard's manager, Mark Griffin, is transitioning the property to organic and keeps 20 beehives on the land.

Griffin uses some organic pesticides but says he prefers maintaining a diversity of insects, which feed on both flower nectar and on each other and, in effect, bring populations into balance naturally. Such a system, though, will always include some pest insects.

"When you're using biological controls, you have to have some threshold for damage," Griffin explains. "Some people have zero threshold for damage. They say, 'Oh, I have a spider mite. Let's bomb this place.' Then you might not have a spider mite anymore, but you have nothing else, either."

Lemon at Littorai Wines says the North Bay's wine country is nothing like the severe situations seen elsewhere in the world, and that the use of the word "monoculture" must be used carefully.

"This is not Iowa," he cautions. "This is not an uninterrupted landscape of corn as far as the eye can see. The heart of our grape industry is, what, the Napa Valley, and that's maybe five miles across?"

Still, Lemon believes that diversifying our agricultural landscape is a requirement for the future, but the change, if it ever comes, will be a slow one. "It will depend on the locavore movement," he asserts, "which needs to convince people to support an agriculturally diverse landscape with their dollars."

Food grown in small quantities, as any farmers-market-goer knows, is relatively expensive, a function of a downsized farm system and increased dependence on manual labor. Preston, too, knows the challenges of marketing small-production food crops. "There aren't markets in most places for small-scale produce," he explains. "What do you do if you have a tenth of an acre of strawberries?"

Sell them at a farmers market, of course. This venue, in fact, may be the chief hope for sustainably farmed, locally grown and sold food. Preston believes so, as does Orchard, though McEnnis says Quetzal Farm has successfully cultivated relationships with numerous small retailers and even Whole Foods.

Though diversification efforts of small farmers like Lou Preston deserve honorable mention, they may be offset by ever more opportunistic vintners and the county governments that abet them. Witness vintner Paul Hobbs' controversial expansions in Sebastopol and Guerneville; or the proposed 154-acre redwood clear-cutting in Annapolis by Codorniu Napa's Artesa Vineyards for even more Pinot Noir; or the 1,769 acres eyed for vineyards by Premier Pacific Vineyards in the northernmost part of the county, and one sees examples of the continued growth of the industry.

Statistics tell a story, too. Of the 101,000 acres of vineyards in Napa and Sonoma counties, more than 5,000 are nonbearing young vineyards recently planted. And though the value of grapes is dropping in both counties, the planting of them goes on and on.

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