San Diego — On January 6, 2003, Suzee Vlk, a 49-year-old resident of Linda Vista, was walking her small dog around the plaza at Old Town San Diego State Historic Park. It would be her last walk. The 49-year-old was crushed by a 100-foot eucalyptus that fell in a Santa Ana wind.

Four more eucalyptus trees are on the plaza. Old Town is the busiest state park in California, with over six million visitors a year. How likely is it that another person will be killed by a falling branch or a failing tree? Are the remaining trees accidents waiting to happen?

I asked John Sevier, a certified arborist with 30 years of experience. "Yeah," he said, "accidents waiting to happen again." What drew him to trees was his interest in safety. He had been in the Air Force from 1966 to 1970, working in flight safety. "I was always intrigued by safety," he said, "and the more I worked on trees, the more I began to realize that trees are nothing but a big series of levers, and if the weight out on the limbs surpasses the strength of the attachment point, you will have a limb failure. Limb and tree failures happen very, very often with eucalyptus trees, and has caused some of the most tragic accidents in San Diego history -- not going back very far to the mid-1980s, when Frieda Williams was killed by a falling eucalyptus limb in the San Diego Zoo."

Sevier was an expert witness in the trial that followed that accident. This part of his business started in 1979, when a lawyer in town contacted him. "A eucalyptus limb hit his client," Sevier said, "Put him in a wheelchair for life. The lawyer simply wanted to know if the accident was preventable. That was back in '79, and I would say from 1979 to 2003, I've probably worked on over 160 tree-accident cases of one type or another."

"What percentage of those were eucalyptus trees?"

"Oh, the majority of either whole tree or limb failure were eucalyptus. The main player in big-tree accidents seems to be the eucalyptus."

"Why?"

"The trees are from Australia. They're used to struggling and reaching out with their roots, under very adverse conditions, to explore the soil to find nutrients and moisture. And when the eucalyptus trees are transported here, to a place like San Diego, and put in places like city parks and state parks, then when the area is irrigated with sprinklers, like here in Old Town, you've got a compromise of the root system. The trees are used to struggling and reaching and surviving without being fed the moisture of the sprinkler system.

"And so two things happen. One, the roots tend to get 'lazy'; they don't reach out and explore, they don't have to go very far to get their moisture. And the other problem with the lawn and irrigation system over eucalyptus is that the lawn acts like a kind of wetting agent, and it keeps the ground soppy around the roots. It never totally dries out. The strength of the roots can be compromised by rot. So you're maintaining a lawn and you're feeding a monster, which is an overwatered eucalyptus tree. What you have is really a very attractive atmosphere to come under and walk under and to be under that is, in fact, a death trap."

Sevier and I were standing next to the tree that had fallen. I pointed to it and said, "So you're saying this tree had a shallow root structure and its roots had rotted?"

"Yes. We can tell by looking at this root ball right here. It's a very, very limited amount of roots that were actually sound and strong and holding the tree, versus the compromised roots -- it just wasn't enough to hold the tree."

"Had there been any warning signs with this tree?"

"Well, certainly experts in the area of eucalyptus trees, which the state park system has -- some very highly qualified experts -- they know that sprinkler systems, lawns, massive root systems, very heavy foliage, and very heavy limbs is a recipe for disaster. What it amounts to is a gamble. It's not a matter of if there'll be a limb failure -- something's going to happen, either a tree failure or a limb failure. The concern I have now after this fatality is that after seeing the park headquarters building over here, if that other tree [he pointed to the nearest eucalyptus] were to fail, it would cut the building in half. The people standing here would be severely injured or killed."

"Do you think the remaining trees present a threat?"

"The remaining trees are in danger either from a whole tree failure or a limb failure. These trees need hazard-reduction pruning, and until that work can be done, the area should be roped off, because people are walking under the remaining trees here, and what it's like is having a bus in your bus fleet that has bald tires and blows out and causes a fatality, and then the rest of the buses in the fleet are still rolling down the road with bald tires! From looking around here, the rationale seems to be, 'Well, we had one blowout, so we're probably good for a while.' "

Representatives from the park had a different view of the potential danger. I spoke with Stephen Bakken, a forester for the state park system. His job is to inspect trees and to train ecologists to recognize and mitigate hazardous ones. I began our conversation by saying, "I assume you pay particular attention to eucalyptus trees."

"Well, no more so than any of the others. Each species has its own problems and attributes."

"So you don't consider the eucalyptus more dangerous?"

"As a general rule, no. Some species we are treating more aggressively now because of the summer branch-drop problems those species tend to have."

Bakken said their usual policy is to examine trees every two years. Some parks do it every year, such as those hit hard by sudden oak death. The program of tree evaluation has been going on for over 35 years.

I mentioned Sevier's contention that it was dangerous to surround eucalyptus trees with irrigated grass. I asked if Bakken agreed. "No," he said. "That's the case with some species of native oaks in California, but it's not necessarily an issue with eucalyptus. I mean, you can obviously overwater something."

"Do the four remaining trees at the Old Town plaza cause any concern for you?"

"Oh yeah, we inspect for root pathogens. That's what we do all the time, especially in a landscaped area."

"Would the tree that blew over be a sign of potential problems with the four remaining trees on the plaza?"

"Possibly. I had inspected the trees in December and didn't find any problems that gave me concern. And I looked at them again after the failure, and I came to the same conclusion."

"When you looked at the one that failed, you didn't see any pathogens?"

"Oh, there were some there. But I recognized that before when I looked at it. I had some concern about the tree, so my recommendation -- and I put it on the records -- was to have the crown worked on. And the tree had also been worked on earlier in the year. The crown had been reduced as well, last spring. We treat each tree on an individual basis and look at its structural integrity and its health. We know we are coming back in one to two years to look at it again."

Again, I expressed Sevier's concern about the danger of eucalyptus trees in public places. "I take it you disagree with him?"

"Well, we've had 30 years' experience. And what do we get? Seventy million visitors a year to our parks. We've had very few deaths, very few injuries. You know, a modest amount of claims. But I'd say, all in all, the program's working reasonably well. Each species has its own attributes, and some of them are compatible with a developed area, others are less compatible with a developed area. You basically have to take that into account if you are planting or replanting or whatever."

"Are the trees in Old Town, then, more compatible?"

"We didn't plant them."

That point was also stressed by John Quirk, chief spokesman for Old Town San Diego State Historic Park. The trees were not originally on the plaza but were planted in the early 1920s, at the latest, by the city. They have been regularly inspected, Quirk said, and "There has never been anything indicated by our internal or external consultants that would predict the massive tree failure that happened in that windstorm. Now that we've had that type of failure, we are evaluating the future of those trees."

Trees Australians have nicknamed "widow makers."