Black Walnut Tree Population Withers in Face of Development : Nature: Despite a colorful and useful history, the trees are becoming increasingly rare. Two of five remaining large groves, and part of a third, are in Ventura County.

For the Chumash, the black walnut tree supplied the dye they used to make baskets and the dice they threw in a gambling game.

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For farmers, the native tree proved the only walnut variety that withstood local pests and fungus. Onto its trunk they grafted the imported trees that would produce a larger, easier-to-crack nut.

Today, eroded by encroaching development, groves of black walnut trees remain in only five places within their entire native habitat from Santa Barbara to San Diego.

Two of those large clusters, each at least two miles long, are located entirely in Ventura County. A third straddles the Ventura-Los Angeles County line and two others are farther south. Individual native walnut trees are found infrequently, scattered throughout the natural landscape in the county, mixed with oaks, cottonwoods and sage.

Not yet threatened with extinction, the walnut woodland is nonetheless becoming increasingly rare.

“The walnut woodland is a unique environment,” said Rick Burgess, a botanist and rare-plant coordinator for the local chapter of the California Native Plant Society. “It’s been wiped out in many areas where it used to occur.”

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The Native Plant Society’s “Inventory of Rare and Endangered Plants” includes the Southern California black walnut on its so-called watch list, noting, “The walnut forest is a much fragmented, declining natural community.”

And the society has included the black walnut in a manual coming out later this month that is designed for consultants planning developments in areas of sensitive habitat.

“That should help,” said Burgess, who works as an environmental planner with the city of Thousand Oaks. “Walnut woodland is a significant habitat and planners should be aware of that.”

The state Department of Fish and Game has also listed the Southern California black walnut on its National Diversity Database, which outlines declining and sensitive habitats.

“There are very few areas of good, intact forest left,” said Mary Meyer, a plant ecologist for the department. In addition to the tree’s value as a plant with a declining population, “walnuts, along with acorns, are a major food source for an array of wild animals,” Meyer said.

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One of the large clusters of forest and woodlands grows on the north slope of Sulphur Mountain overlooking Ojai; another is in the Hopper Mountain National Wildlife Refuge in the Los Padres National Forest above Piru.

A third cluster is on the north slope of the Santa Susana Mountains from west of the Ventura County line to the intersection of the Antelope Valley Freeway and Interstate 5, while another is on the north slope of the Santa Monica Mountains in Los Angeles County. The fifth is in the Chino Hills in the northern part of Orange County.

The larger concentrations of the trees, with their whitish trunks and bright green leaves, are found on north-facing slopes and deep canyons, but smaller groves of the native walnuts can also occasionally be found in areas throughout the county.

One colony is located near North Ranch in Thousand Oaks. An offshoot of the Sulphur Mountain cluster grows west of the Ventura River below Casitas Dam.

Only about 10% of the land where the trees now grow is in public hands, mostly in the Los Padres National Forest, with the remainder held by private property owners, said U.S. Fish & Wildlife Service botanist Tim Thomas.

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That means the privately held land could be vulnerable to development, he said. But he said there are inadequate measures available to protect plants before they become rare and endangered.

“Why wait until things are relegated to the point where they will disappear with the next development?” Thomas asked. “Why not try to protect these systems before they get that far?”

The Southern California black walnut, whose leaves turn bright yellow before they drop in the fall, has a useful and colorful history that at least dates to the area’s native inhabitants, Thomas said.

The Chumash used the black, net-like husk inside the leathery skin that holds the hard shell and nut as dye for coloring baskets. They also used the nuts as dice for a gambling game after splitting them in half and decorating them with shells and designs.

In addition, the Chumash used the nuts as a supplemental food, Thomas said.

“It’s got a tasty meat,” he said, cracking open a nut he retrieved from under the canopy of one of the trees near Foster Park.

He pointed to one nearby tree, with five trunks, each about 10 inches in diameter, jutting from the ground.

“Their response to recovery from fire is to continue to put out trunks from their basal root systems,” he said. Many trees have five trunks, though some can have as many as 20 in various stages of life and death.

“They begin to look like an upside-down octopus,” he said.

The leaves also make the tree distinctive. Each leaf is actually composed of many long, thin leaflets. They are lighter in color than the leaf of an oak and catch sunlight more easily. On a recent trip, the sun’s morning light appeared to spotlight the leaves.

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The native walnut has also proved useful to growers who later settled the region. When they first tried to plant Persian or English walnuts in Ventura County several decades ago, a fungus wiped the trees out. The imports were not resistant to area pests.

The solution, which is still used today, was to plant native walnuts as rootstock and graft on branches from imported trees to produce the commercial-variety nut.

But there is another reason that the native walnut and its habitat should be preserved, Burgess said.

“It’s something that evolved over time and it has a right to live,” he said. “I just don’t think we can be so presumptuous as to destroy a species because we want another Target or Kmart,” Burgess said.