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Features May 2004: Volume 1, Number 2
   

Tree Wars
The Secret Life of Eucalyptus
By Heather Henter

 
     

Some people love them, some people hate them. But after years of assault by man and insect, it looks like these Aussie interlopers are here to stay.

The University of California, San Diego is not an urban campus with an edgy feel. It is not a campus with hundred-year old buildings or broad manicured lawns divided into traditional quads. UCSD is a campus with eucalyptus trees. Tall and columnar, pungent, with bark so gray it almost blends in with the surrounding concrete, eucalyptus trees are more than a leafy backdrop. They are part of the University’s history, character and ecology. The trees, as symbolized by Terry Allen’s talking “Trees” sculpture, speak to us, sometimes quite literally. But what people hear is different.

To some people, what the trees say is the essence of the campus. “The eucalyptus grove helps to define the place,” says Sue Peerson, director of Physical Planning for the University. “I think it is what people identify with UCSD.”
To others, what the eucalypti say is environmental blasphemy. Like many residents of California, eucalyptus trees are not from here. That is a problem, according to those concerned with protecting California’s natural environment. Simply by being here the eucalyptus trees preclude native vegetation, and the animals that go with it. “The people I know think of them as giant weeds,” says Cindy Burrascano, conservation chair for the San Diego chapter of the California Native Plant Society.

But despite such criticisms, as well as onslaughts by insects, bulldozers and vandals, 220,000 eucalyptus trees remain on campus. Beloved by some, loathed by others, the eucalyptus is the quintessential survivor. How can these trees be an artist’s inspiration as well as the focus for such condemnation?

A Long History
Eucalypti, also called gum trees, are native to Australia, where more than 700 species have evolved in geographical isolation over the past 40 million years. Nurserymen and horticulturists initially brought the trees to California in the 1850s as a new source of fast-growing timber. Parts of California had relatively few large trees, and the burgeoning population was quickly chopping those down. Community leaders forecast an impending timber famine and the eucalyptus was seen as the salvation.

The early supporters of eucalypti in California zealously promoted the trees with the fervor and faith of evangelists. An article in a 1910 issue of San Francisco magazine states: “By the possession of a few acres of this timber all fear of the future may be stricken from a man’s life.”

The supposed uses of eucalypti were far-ranging. As a source of lumber they could save the shipbuilding industry; they could be a source of firewood, coal and potash, and they would make California a hub of furniture manufacturing. The healthful vapors could even prevent malaria.

Early reports refer to it as the “fever tree” because there were reductions in the number of malaria cases where it was planted. The decline in malaria was probably real, but not because of the trees’ salubrious odors. Malaria is transmitted by mosquitoes, which breed in standing water. Fast-growing eucalyptus trees use a lot of water. When they were planted in marshy areas the swamps dried up, eliminating mosquito-breeding spots and thus reducing transmission of the disease.
In San Diego, eucalypti were planted for timber, for windbreaks and as ornamental shade trees. “In the 1860s and 1870s eucalypti were planted everywhere,” relates Iris Engstrand, specialist in San Diego history and professor at the University of San Diego. “They were hardy, easy to grow, and you could chop them down and they came right back.” In Rancho Santa Fe the trees were planted for railroad ties, but it cracked and split, proving no more suitable for the railroads than it had for shipbuilding and furniture making. In the end, most eucalyptus timber in San Diego was probably used for firewood.

UCSD’s Eucalyptus Trees
Around the turn of the century, San Diego was a boom-and-bust place. The year 1910 was the bust part of the cycle. Unemployment was high and the jail was overcrowded. The city had recently abolished the use of the city rock pile as a make-work project for prisoner chain gangs. In this climate the city set up a municipal penal farm on unused public land to the north. It is called Torrey Mesa and it is where UCSD now stands.

The city hired 23-year-old Max Watson, son of a Unitarian minister, as the city forester. Watson advertised that he would pay 50 cents and room and board for a day of honest labor and a chance to get back on one’s feet. Over the next several years 400 destitute men, and prisoners on a rudimentary work release program, made their way to the municipal farm. Newspapers referred to the farm as Watson’s “Hobo Camp.”

The workers planted subsistence crops as well as anything that Watson thought could make a profit for the city. At one point Watson suggested a “drug farm,” a farm for plants such as foxglove and ginseng that had medicinal value. That plan never materialized, although the idea seems a precursor to the current concentration of pharmaceutical research companies on the same mesa.

What those indigent men did plant, however, were 300,000 eucalyptus trees, mostly sugar gums (Eucalyptus cladocalyx). Citizens had high hopes that the great profit from the timber could reduce taxes. A San Diego Union headline on New Year’s Day, 1912, read, “Trees to Defray Taxes in Future”. A national magazine called Technical World was equally optimistic: “San Diego is one of the first American cities to inaugurate a great forest enterprise in the expectation of speedily lessening the burden of taxation borne by its citizens and possibly of ultimately relieving them of all tax levies for the support of city government.”
It did not quite turn out that way. According to David Kuntz, a former University of San Diego graduate student who did research on Watson, the city never realized a profit, either because of poor city management or changing economic times.

That said, the trees on Torrey Mesa were used for something because they have been cut down and regrown from their stumps. “Around 95 percent of the trees were coppiced before the campus was here,” says Phil Peters, head tree trimmer for the University. “Some of them have been cut two or three times.”

There are exceptions. The sugar gums in front of the Chancellor’s complex and the towering blue gums, a different species, between Urey Hall and the Main Gym are among the few eucalyptus trees that survived the century without ever meeting the wrong side of an ax.

The last remnants of the trees from San Diego’s municipal farm now wind their way through the UCSD campus. In some places, such as the grove behind the Student Health Center, the straight rows of trees in a grid pattern are a window into the former industrial plantation. What had once been a cash crop planted by a group of destitute men now forms an architectural reference point for a university.

A Battleground
Although early San Diegans thought the eucalypti on Torrey Mesa were salvation itself (in the form of a lower tax bill), the trees have often been under attack. One of the most serious battles has been against an insect.

When horticulturalists first brought eucalyptus trees to California, they arrived as seeds and were not accompanied by any of the herbivorous insects that feed on their leaves or wood. For more than 100 years, eucalyptus trees in California were pest-free.

All that changed in 1984 when an Australian beetle, the eucalyptus longhorned borer (Phorocantha semipunctata), showed up. Scientists first discovered the beetle in Orange County, but they found an infestation at UCSD shortly thereafter. No one knows how it got here. There has been speculation about eco-terrorists determined to right the wrongs of non-native tree species, but it is just as possible that the beetles inadvertently hitched rides in shipping crates made out of eucalyptus wood. Whatever way they arrived, the eucalyptus groves at UCSD were hard hit, and entomologists had to employ a creative type of pest management to do combat.

The eucalyptus longhorned beetle is striking—a large, shiny black beetle with bold stripes and long antennae that stick out like the ends of a handlebar mustache. The beetles are attracted to airborne chemicals produced by injured or stressed trees. Like reporters hovering outside a high-profile court case, the beetles swarm to a vulnerable tree. The adult females lay their eggs under the bark and the beetle larvae do all the damage as they chew their way through the cambium layer of the tree and quickly girdle it. There can be so many larvae feeding in one tree that you can hear them. “They sound like Rice Crispies after you put the milk on,” says Larry Hanks, an entomologist at the University of Illinois. “Snap, crackle, pop. All those innumerable little mandibles chewing on wood.”

Once beetles attack, a tree dies quickly, in as little as two weeks. After the larvae metamorphose into adults, thousands of them will emerge from a large tree, filling the air with flying beetles. “It’s like a plankton bloom,” says Peters, the tree trimmer.

In the late 1980s and early 1990s, hundreds of trees were killed on the UCSD campus each year, including many large and stately individuals. “I have taken care of these trees for my whole career,” laments Peters. “When we lost some, it was like losing old friends.”

But in 1992 there was a breakthrough. A scientist working in Australia found beetle eggs that were parasitized by a tiny wasp, not much bigger than a grain of black pepper. The wasp, Avetianella longoi, is a specific type of parasite, a parasitoid.

Charles Godfray, an entomologist at the University of London, likens the biology of parasitoids to that of the creature in the 1979 sci-fi movie Alien. While their space ship is traveling back to earth crewmember Kane (John Hurt) unknowingly becomes infected with the immature form of an alien being. After a time in the sick bay Kane recovers, only to have the adult alien burst out while he and the crew are eating breakfast, killing the hapless Kane in the process. Parasitoids do the same thing here on Earth, but fortunately only to other insects. In the case of A. longoi, its hosts are not space travelers but rather the eggs of the eucalyptus longhorned borer.

Parasitoids are the darlings of biological control, which uses natural enemies, such as diseases, parasites, or predators, to fight a pest. Like many parasitoids A. longoi has a narrow diet, it only parasitizes a few species of hosts, which reduces its impact on the rest of the environment.

As the beetle spread throughout Southern California, a team of scientists at UC Riverside, where Hanks was at the time, imported A. longoi from Australia. Some eucalyptus opponents looked askance at this project—an introduced parasite used to fight an introduced beetle that was attacking an introduced tree. Others felt eucalyptus trees were too valuable to jeopardize.

In 1993, the team at UCR, which besides Hanks included professors Jocelyn Millar and Tim Paine, devised a plan to distribute these wasp carnivores to sites around Southern California, including UCSD. The first task was to collect beetle eggs. That was easy. The beetles, apparently desperate to reproduce, will lay their eggs on virtually anything. Hanks provided the beetles with filter paper in a Petri dish, “You can’t get more bleak than that,” he notes.

Hanks then exposed the egg-covered paper to wasps, so the wasps could lay their own eggs in the beetle eggs. Finally, Hanks brought the parasitized eggs to campus, slipping the paper under tree bark.

Hanks used the rather desolate grove north of Geisel Library as a study site. There are trees, running paths and a sports track in this grove but not much else. Counting bugs, crawling through the bushes and peering under tree bark is unusual adult behavior under any circumstances, and Hanks got his share of strange looks.

“When I emerged from the bushes, sweaty and with sticks in my hair, I think I startled a few people doing their push-ups,” Hanks remembers. But no one ever disturbed him while working. “When you do something weird, people don’t stop to ask questions. They just walk somewhere else.”

Then it was up to the wasps. And they attacked the beetles voraciously. Hanks found naturally parasitized eggs almost immediately after the releases. But a large hurdle remained. Winter. Lab tests showed that the wasps could stand temperatures colder than those San Diego had to offer, but a more vexing problem remained—what would these tiny creatures do throughout the colder months? The beetles become completely inactive in the winter, so no new eggs are produced.

“We didn’t think it would be too cold here, but it could be too warm,” says Hanks. “If the wasps came out in January, there would be no fresh eggs and the wasp population would go extinct. The adults only live for a few days.”

The only way to answer this question was to wait. And wait. When they found freshly parasitized eggs the following spring Hanks and colleagues breathed a collective sigh of relief. Not only were the wasps established, possibly the most critical stage of any biological control project, but they also were parasitizing hosts in ever increasing numbers. By the following year, about 90 percent of the beetle eggs that Hanks found were parasitized. The eucalyptus longhorned borer is no longer a problem on campus.

Like most science stories, however, reality is complicated. The champagne had barely stopped flowing in celebration of this biological control success before another pest showed up. A beetle very closely related to the eucalyptus longhorned borer was discovered, and this beetle’s eggs are mysteriously resistant to parasitization by A. longoi. No similarly effective biological control agents have been found for this pest, but tree mortality is nothing like it was a decade ago. Both Peters and Hanks speculate that the most stressed, and thus vulnerable, trees have already been killed; tree resistance is now as important a pest control factor as is biological control. Other eucalyptus pests have since appeared on campus and across the state, however, such as the red gum lerp psyllid (Glycaspsis brimblecombei), the eucalyptus tortoise beetle (Trachymela sloanei), and the lemon gum lerp psyllid (Eucalytolyma maideni). And the eucalyptus trees soldier on.

The Besieged Trees
While entomologists are trying to save the eucalyptus, other people seem to have a grudge against them. Vandals have pulled trees down with their cars, stomped on new plantings, ripped off limbs and even injected herbicides into trees. Poison killed about 50 trees in the north grove. No one knows who is responsible for this vandalism or exactly why.
Bulldozers have also taken their share of the trees. Whenever the campus grows, open space shrinks, although the current campus land-use plan dictates that whenever trees are cut replanting must occur elsewhere. But that has not always been the case. In the early days, the few buildings on campus were surrounded by a forest of eucalyptus. That has changed.

But the major criticism of the eucalyptus is that wide-scale planting has displaced native vegetation, such as the coastal sage scrub and oak woodland, which flourished on UCSD land before 1900. As can be easily seen in the UCSD eucalyptus groves, there is little or no understory of shrubs below a Californian eucalyptus forest. The groves are almost “totally devoid of other species,” says Burrascano, of the California Native Plant Society. “I think of it almost as a dead zone.”

Eucalypti inhibit the understory in two ways. They suppress other plants both chemically and by the sheer quantity of duff or leaf litter. Other plants simply cannot germinate. This is probably exacerbated by the high density with which the trees were originally planted on the UCSD campus.

Although some native fauna now depend on eucalyptus groves, there are undoubtedly many other animal species whose populations have been hurt by the monocultures of this exotic tree. “An oak woodland has a much wider variety of plants and animals,” says Burrascano.

What Does the Future Hold?
Clearly eucalyptus trees are an important part of campus history, but will they be part of its future?

Yes. Whether you love them or hate them, the eucalyptus trees at UCSD are here to stay. The campus land-use plan emphasizes the rustic environment the trees create and the historic significance of the grid plantings. Campus planners hope to replant that grid where necessary to maintain the historic feel of an industrial plantation. They also hope to reduce the density of overcrowded trees in the outlying groves, which will invigorate the remaining trees and might also help native understory species to infiltrate.

Peerson from Physical Planning summarizes her feelings about the trees: “Even though it’s a man-made environment, the remnants of that (the historic grove) have really become a signature open space that weaves its way through campus. It’s something we want to protect and preserve.”

So what do the trees say to us? Two of Terry Allen’s talking “Trees” sculptures play an eclectic mix: country, jazz, Navajo chants, some David Byrne. But the third tree sculpture in front of Geisel Library, which is molded around a tree cut down to build the Jacobs School of Engineering, is strangely, and gracefully, silent. Is that tree reminding the campus that the history of a place is more than its buildings? Is its silence asking the community to imagine what the campus would look like without the trees?

Peters, who has the job of cutting down the trees the campus does not want, has thought a lot about what the eucalyptus trees bring to the University. “Without the trees and the open space that UCSD has,” he says, “the campus might look like, well ... UCLA.”

Heather Henter is a freelance writer and a researcher in the Section of Ecology, Behavior, and Evolution at UCSD.

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Terry Allen - Trees
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"Despite onslaughts by insects, bulldozers and vandals, 220,000 eucalyptus trees remain on campus."