Bark Beetle’s Bite Threatens Torrey Pines

The picturesque Torrey pines that cling to the sandstone coastal bluffs and hillsides north of La Jolla hold a dubious distinction: They are the rarest species of pine in the United States.

With a tiny coastal habitat stretching little more than 4 miles from Del Mar through the Torrey Pines State Reserve to the south, this singular tree is a revered part of the landscape, jealously protected from the whims of modern man like a rare jewel in a banker’s vault.

But the gnarled and shapely trees face a troubling new threat. Weakened by two years of drought and several days of hellish heat in late summer, the trees have been hit by a bark beetle infestation that, if unchecked, could seriously deplete the unique nature reserve.

The pest, dubbed the “confused five-spined beetle” because of the aimless path it bores under the bark of a tree, has already killed a dozen Torrey pines at the 1,750-acre park and threatens to lay low more than 100 others. State officials worry that the problem could spread further through the park’s Torrey pine population, estimated to number 7,000.

“We’re deeply concerned and a bit alarmed at the extent of the infestation,” said Bob Wohl, supervising ranger at the reserve. “It’s located in the heart of the park, the areas with the highest visibility and the most prominence.”

For now, park officials are sitting tight. They remain hopeful that rain will continue through the winter, bolstering the health of the pines and increasing the production of sap, which helps ward off the pests.

“We hope the rain we’ve had since Thanksgiving Day and the tremendous drop in temperature will knock the beetles off,” Wohl said. “Everyone in San Diego County wants good weather, but we’ve been sitting up here saying, ‘Freeze! Plummet! Give us rain!’ ”

If the pests are still prevalent by spring, however, authorities say they probably will have no choice but to launch a counterattack, even though park

policy encourages a laissez-faire management approach to help maintain the ecosystem of the reserve.

Bill Tippets, a state park ecologist, said officials would probably begin by thinning out unhealthy trees. Under that scenario, the bark on infested pines would probably be stripped to create an inhospitable environment for the beetles. If necessary, some of the affected pines might be cut up and hauled out of the forest.

May Have Served as Incubators

Authorities suspect that some weakened and fallen trees have served as incubators, encouraging the beetles to reproduce and send out new troops to plunder and pillage.

Insecticides would be considered only as a last resort. Tippets said authorities prefer not to use the chemicals because they usually are only partly successful and might kill insects that may serve as predators to pests such as the confused five-spined beetle.

The beetle, Ips paraconfusus, hardly looks the part of a feared invader. Less than a quarter of an inch long, it has a dark brown body and tiny antennae with rounded ends. The slow-moving, winged insect is capable of wandering among several trees during its lifetime.

It attacks a Torrey pine by devouring the cambium layer, the thin coat between the bark and inner hardwood that serves as the circulatory system for the tree, processing photosynthetic products as well as nutrients tapped from the ground.

A male beetle finds a tree that is susceptible--usually a pine weakened by drought or aging--and sends out a sex attractant that lures females. Together, they hollow out a larval chamberin the tree, where the female lays eggs. It is the hatched larvae that do most of the damage, burrowing a tortuous course through the cambium layer.

As a result, the clusters of needles that characterize the Torrey Pine begin to drop. If the larvae circumnavigate the trunk of a tree, severing the cambium layer, which connects roots and branches, the pine will eventually die.

A Doomed Tree

On a tour of the grove, Wohl pointed to a graying tree. Reaching up, he grabbed a small branch and, with an easy twist, pulled off a ring of bark, proof that the tree had been infested.

“I would say what we’re talking about here is a doomed tree,” he said.

Wohl said rangers noticed the problems in April, when the needles on several trees began browning and dropping off. The problems persisted through the summer, and Wohl figures the coup de grace came when several days of 100-degree temperatures produced a “blast-furnace effect on the trees.”

By Labor Day, local experts had isolated the beetles as the problem. In mid-December, a state forest pathologist came from Sacramento to conduct tests. His results concurred with the findings of local authorities: The drought had weakened the trees enough to allow the infestation.

Much like the continuous battle between a human’s immunological system and germs, Torrey pines fight a never-ending war with the beetle and other pests indigenous to the environment. A healthy flow of sap serves to repel the invading hordes, pushing their eggs out or encasing an attacker in a coat of resin.

“The bark beetles are always here, but the trees can normally repel them,” Wohl said.

Spread to Prominent Spots

The problem has spread to several of the most prominent spots in the park, along the Guy Fleming, Razor Point and Parry Grove trails. Those areas feature some of the oldest and most beautiful trees in the park. (Torrey pines can live about 300 years.) The beetles have also spread to several trees surrounding the old adobe lodge that serves as park headquarters.

Once known as the soledad pine, the trees were renamed in 1850 by Dr. C. C. Parry, a botanist for the U. S. Mexican Boundary Survey. Parry chose the botanical name Pinus torreyana, or Torrey pine, in honor of his former botany professor, Dr. John Torrey.

In 1883, Parry returned to the site and began urging that the land be acquired to preserve the species from what he feared would be certain extinction at the hands of man. The city of San Diego helped the cause in 1899, when 369 acres were designated public parkland.

Philanthropist Ellen Browning Scripps acquired adjacent groves in the years that followed, and those lands were added to the park in 1924, when it was enlarged to nearly 1,000 acres. In 1979, a 154-acre extension was formed on the sloping hillside to the north of Los Penasquitos Lagoon.

Infestations have probably occurred many times through the eons. Most recently, a bark beetle infestation killed 18 trees in 1984 and 1985 on the slope leading from North Torrey Pines Road to Los Penasquitos Lagoon. Eventually, rains helped bolster the surviving trees, and they were able to repel the beetles.

Some authorities suggest that Torrey Pines State Reserve’s trees have been weakened of late not only by the drought but by the increased competition for water among the pines. In addition, chaparral and other brush have spread through the forest, further tapping what nutrients and other resources are available.

Torrey pines are known to exist only one other place: on Santa Rosa Island, one of the Channel Islands southwest of Santa Barbara.

The minute range has helped propel the trees to the front of the hearts and minds of many San Diegans. The Torrey pine is, indeed, a home-grown tree, and many local residents chafe at the thought of even one falling to a predator.

But some experts say the infestation, although troubling, in many ways is simply Mother Nature at work thinning the forest, allowing the strongest to survive.

Wohl noted, however, that there is a “difference between thinning out and wiping out.” The beetles seem to be indiscriminately hitting young, middle-aged and old trees in certain sections of the park.

“You can get into a lot of Darwinian arguments about natural selection and such, but it seems to me this infestation has more to do with proximity than anything else,” he said. “It’s more like a contagion. If you live next door you’ll get it, but if you live down the block you won’t.”