Grasshoppers Take Bite Out of Plan to Save Oaks : Environment: Insects ravage seedlings planted by state to preserve species. Endangered trees have not been restocking themselves.

It was fine until the grasshoppers came.

Up to that point, the state was finally managing--on a gentle slope of forest, after two failed attempts--to grow the imperiled Engelmann oak, whose seedlings no longer seem to mature in nature.

Caltrans has launched a planting program of 780 oaks that employs a solar-powered drip irrigation system similar to one used by marijuana growers. The project could become a model statewide, officials said.

Although foresters thwarted the seedlings’ traditional enemies--parched earth and the gnawing teeth of cattle, deer and gophers--they neglected to plan for an unusual seasonal guest: grasshoppers.

In Love Valley, a meadow of Cleveland National Forest dotted with mature oak trees, occasional deer saunter by, and squirrels zigzag amid the grass browned by summer. Large yellow and black spiders, called argiopes, spin webs that glint in the sun.

The valley seemed still when Roger Wong of the U.S. Forest Service recently surveyed the 20 acres of foot-tall Engelmann oak and coastal live oak seedlings planted in May. But as Wong stepped forward, a small cloud of grasshoppers sprang up out of the tall grass. And clearly, the voracious insects have wreaked havoc, stripping bare some seedlings, leaving half-eaten leaves on others.

Wong can only groan. Before the grasshopper infestation hit last month, he had estimated that about 95% of the tiny oak trees would survive--a bold prediction, considering the past.

The first effort by the Forest Service had managed to grow 10% of the trees planted. Foresters at UC Agriculture Extension tried again in 1989, planting more than 600 seedlings and giving them a squirt of water and fertilizer, Wong said. That time, none survived.

So for this latest effort, foresters coddled the trees with protective mesh screens and a drip irrigator.

“We thought of everything, everything. Except grasshoppers,” Wong said. “I never had to deal with grasshoppers before. I never thought that would be a problem.”

Centuries ago, the Engelmann oaks grew throughout southeastern California, Arizona and Baja California. But as civilization and urbanization spread, the territory of the Engelmann oak has diminished further.

Today, the Engelmann oak persists in scattered groves, 93% of which are in San Diego County and 6% in Riverside County, all in the general area of the national forest. They occupy the smallest range of any mainland oak. But, perhaps scariest of all for oak enthusiasts and conservationists, the Engelmann oak has become extremely vulnerable because it is not restocking itself--the population of older Engelmann oak trees is not being replenished by young saplings.

“It’s very much a case of dwindling numbers in terms of Engelmann oaks,” said Jim Dice, president of the San Diego Chapter of the California Native Plant Society. “We don’t know what we are losing when we wipe something out. We do know we are losing open space and things we once took for granted, like the Engelmann oak.”

Experts say there are a number of reasons why the Engelmann oak is not replacing itself. Pocket gophers, mice, ground squirrels and other rodents that enjoy munching acorns and tender young oak roots have proliferated in the absence of their natural predators--bobcats, gray fox, coyotes and badgers--said Pavlik, author of “Oaks of California.”

Throughout the Southland, indigenous grasses have been overtaken by non-native weeds that form a thick herbaceous carpet. The dense layer of growth vies with oak seedlings for the soil’s nutrients, often choking the young Engelmann oaks.

“No matter where the acorns fall, if they are not eaten by critters, they are going to be competing with these weedy grasses,” Pavlik said. “We think it’s a major factor.”

Historically, grass fires opened up the weed layer, enabling oak seedlings to poke through. But the reluctance to burn areas in recent years has allowed the weeds to become entrenched in many regions, Pavlik said.

Widespread grazing and cattle movement have packed the soil, making it difficult for rainfall and oak roots to penetrate. The livestock also enjoy nibbling oak leaves.

To further complicate matters, about 80% of the state’s oak woodlands are on private land--putting them out of reach of conservationists, Pavlik said. Foresters now realize that they have omitted the oak in their preservation efforts.

“The state spent so much time and effort on conifers. Protecting hardwoods is something we neglected for a long time. Only now are we beginning to realize we’ve eliminated a lot of hardwood,” Wong said. “We didn’t look into regenerating oaks until now. Oaks are very difficult to regenerate--that’s another one of our problems.”