Preemptory strike on eucalypti

Today, December 15, the city was set to begin removing three Coronado eucalyptus trees, longtime residents of Spreckels Park. An assessment by the city’s arborist found the sweet-scented trees, which are similar in size and age as one that shed a seven-ton limb in October, pose a public risk.

Several species of the Australian natives, imported in the 1850s, now flourish throughout the state. Popular in parks, the trees have led to property damage, injuries, and deaths. Their “widow maker” nickname was earned long ago.

By October 12 this year, the University of California’s Tree Failure Report program had received 5800 statewide accounts of trunk breaks, branch breaks, and uprooting. Among the four tree types most often involved were eucalyptus.

Many other incidents went unreported, like the October 15 crash-landing of the eucalyptus limb in Spreckels Park, which the city’s arborist, Mike Palat, attributed to “sudden branch drop.” Signs of decay were found, and the tree, considered likely to fail in the next two years, was destroyed. A reassessment of the trees now being removed found them weakened as well.

Is drought the cause behind the rash of falling branches?

“I don’t think that drought affected the trees too much since they are located in an irrigated park,” said Palat. El Niño wasn’t a factor in the decision-making, either. “The assessment was based on normal, seasonal weather conditions,” he said.

One sugar gum eucalyptus, with its large limbs stretched over the playground, was too weak to spare. Past topping of the tree has led to decay and fast growth, and no apparent way to reduce risks. A second sugar gum, on another corner of the playground, has a limb that appears to be dying, sprouting fungal fruiting bodies at its base. The likelihood of its failure in the next two years was also deemed “probable.”

The third tree is a red box eucalyptus near the park’s restroom. It was included due to a recent limb loss; a regular occurrence despite pruning, according to city documents. One break was mid-branch, “which could not be predicted or explained.” Since that particular variety of eucalyptus is uncommon in Southern California, “there is scant information as to the failure profile in the region.”

Which is exactly why the Tree Failure Report program was started in 1987. Understanding why, when, and where urban trees topple is the goal. Arborists statewide are encouraged to submit reports, which get entered into a database to build “failure profiles” for different trees that may one day help prevent the problems.

“Our hardest job is trying to convince arborists to document the failures they encounter,” says Katherine Jones, the program’s database manager. She admits it hasn’t been a banner year for reporting, with far fewer contributions than usual. “We’re working on getting an app,” she said.

In the 1980s a child was crushed to death by a eucalyptus tree at the San Diego Zoo, which then began replacing them with sturdier varieties like oaks. In 2011, a Newport Beach woman was killed by a falling blue gum eucalyptus while driving. Another driver fatality occurred in March 2014, in Solano County.

Eucalyptus trees are known to lose branches in the summer or tip over without warning. The blue gum, which grows very large and heavy, is considered especially prone to surprise drops.

“This happens when temperatures are high, with no wind or precipitation, and no obvious structural defects are noted,” Jones said. “Summer failures are less common for many species, but in the case of blue gum it’s about equal.” Winter failures often go with stormy weather.

But the causes of limb failure aren’t always obvious, even in parched California where 12 million trees died over the past year from lack of water, according to the U.S. Forest Service. Herbicides used to kill the understory and crowding by neighboring trees also leave their marks, for example. One problem can lead to another, weakening trees, making it harder to learn why they fail.