Why are so many Bay Area trees turning destructive and deadly in recent storms? The answer is years in the making

Weakened by years of drought, Bay Area trees toppled over in wind, rain and snow. Are certain trees more at risk?

The same urban canopy that provides so much relief in the Bay Area’s summer is now exacting a winter toll, with hundreds of trees weakened by years of drought collapsing in relentless rain and wind — claiming lives, buildings and roads.

“Like for us humans, it takes a little bit of time to recover from stress, the lack of water and high summer temperature,” said UC Davis ecologist Alessandro Ossola, who specializes in urban areas. “Some of our trees are failing to adjust to newly wet soil and atmospheric conditions….they’re simply unable to cope when climate and environmental conditions revert too fast.”

In nature, downed trees are not a problem, but a benefit. They renew the forest by creating a home for fungus, insects, wildlife and sunlit space for new seedlings.

But in neighborhoods, they have been destructive and deadly. On Tuesday, during the last in a series of strong atmospheric river storms, trees claimed the lives of five people in the Bay Area — from every walk of life, in different circumstances.

In San Francisco, 36-year-old Ryan Taylor, visiting from Las Vegas, was killed by a toppled tree at Post and Polk streets. Qiaoying Han, 55, of San Francisco, was waiting at a bus stop near 23rd Avenue and Lincoln Way by Golden Gate Park when a large branch snapped in the wind and landed on her.

Walnut Creek-based attorney Thomas Huster, 79, was killed driving home from dinner with his wife in the retirement community of Rossmoor when a eucalyptus tree crushed their Tesla. In Portola Valley, 29-year-old Jesus Ivan Cruz had just finished a plumbing job when a tree fell onto his white van on Alpine Road west of Interstate 280. At Oakland’s Lake Merritt, Louisiana native Tyrone Butler, who was devoted to church and music, was killed inside his tent.

At least three others have died from falling trees since the storms began walloping Northern California late last year, including a 2-year-old child.

Trees have also damaged homes, crushed cars, blocked roads and pulled down power lines. Arborists are scrambling to keep up with the demand.

“Every day, we’ve had one emergency after another after another,” said Blair Glenn of Saratoga Tree Service. This week, with ropes and chainsaws, Glenn and his crew worked like aerial surgeons, removing a redwood from an elegant Mediterranean home and an Atlas cedar from a church. “I’ve got a list of 20 more calls and I can’t get to them all. And a lot of these jobs are pretty tricky.”

In Concord, Shelley Mack counted up her casualties throughout the winter: A gazebo. Koi pond. Fences. Animal pens. Water pipes. A PG&E transformer and power lines. A carport. Part of a patio. A Ford Fusion Hybrid car. A white SUV.

“Every time it rains, we freak out,” said Mack of BBB Pet Rescue, where nine of 40 eucalyptus trees toppled this winter — and the rest are leaning precariously. With her elderly landlady unable to afford the cost of tree removal, and no help from the city, county, Red Cross or FEMA, she is desperately fundraising.

Some of the region’s grandest trees have met their fate. Lost was the giant oak at Napa Valley’s V. Sattui Winery, where thousands of visitors once picnicked. In Palo Alto’s Mitchell Park, a venerable stone pine — a perch for generations of children — also fell. San Francisco’s Stern Grove lost about 120 trees.

Winds sheered off the trunk of one of the oldest plants at UC Berkeley’s Botanical Garden, a redwood that pre-dated creation of the campus. When it fell, it struck an ancient buckeye.

“One historic tree took out another historic tree. There are splinters and logs everywhere,” said Andrew Doran, director of collections at the garden. The storm also claimed an endangered Picea spruce, part of the Garden’s only Parana pine, an unusual species of Eucalyptus and a gum-leaf cone bush from Southern Africa.

A strong prevailing wind with saturated soils can eventually overcome a root system’s anchoring, especially if a tree has been stressed by drought, said Dave Mason, spokesman for the East Bay Regional Park District.

Even healthy trees can be damaged by sustained winds above 50 miles per hour, said experts. But wind from unusual directions can cause damage at lower wind speeds. Short bursts of wind can snap trunks if there is a point of weakness.

Limb breakage may not be a flaw, but a tree survival strategy, said Mark Vande Pol, who has a decades-old native plant restoration project on his Santa Cruz Mountains land. He said that some trees, such as a genetic variant of the Coast live oak, have bark “crotches” that seem designed to drop under extreme loads.

High rainfall and winds are particularly problematic for some large evergreen tree species that keep their leaves “on” during the winter storm season, said experts. The leaves store water and act as a sail for fast winds. Dense canopies of oaks and buckeye trees also capture snow, which caused chaos during February’s storm. In contrast, deciduous tree species are much less prone to weather damage.

But no particular species topples over more often than others, according to Cal Poly botany professor Matt Ritter. For instance, while eucalyptus have a bad reputation, there’s no data to support that. Their problems are just more apparent because they’re so widely planted, he said.

“We’ll move on,” said Doran, as he plans how to best restore UC Berkeley’s famed garden. “It’s an enormous loss, and we do get emotionally attached to plants. But it clears the way for quite a number of other things.”