Beware of Falling Trees and Other Lessons from San Diego’s Weird Weather - Voice of San Diego

Science/Environment

Beware of Falling Trees and Other Lessons from San Diego’s Weird Weather

• During one stormy January weekend, 543 trees fell citywide; 374 were street trees, the rest were in parks and open spaces.

• The city released its draft Urban Forest Management Action Plan on Jan. 15, a working document intended to guide the city’s efforts to inventory, assess and maintain existing trees while making plans to plant more.

On an unusually wet and windy weekend at the end of January, San Diego’s ecosystem responded in a bizarre if inevitable way: Hundreds of trees fell over.

As wind gusts topped 60 miles per hour, the city of San Diego received more than 500 calls in a 36-hour period from citizens concerned about damaged and downed trees. City officials determined 543 trees fell citywide; 374 were street trees, the rest were in parks and open spaces.

The tree loss would be bad in any circumstance, but it was particularly disappointing since the city has been ramping up its efforts to boost the local tree population.

How Does This Happen?

Uprooted trees caused widespread property damage and at least one fatality that January weekend. Torrey Pines Golf Course lost iconic eucalyptus trees amid the Farmers Insurance Open, a 10News reporter and photographer on assignment in Mira Mesa were injured by falling eucalyptus and a woman was killed when her car was crushed by a toppled Torrey pine in Pacific Beach.

Local arborists and meteorologists say circumstances uniquely aligned for this type of large-scale tree failure. The ground was wet with rain while powerful onshore winds tested the strength of tree roots parched by drought conditions and state-enforced water use restrictions.

Even well-intentioned efforts to boost San Diego’s tree canopy likely contributed, said Robin Rivet, an arborist who sits on municipal forestry advisory boards in San Diego and La Mesa. Urban planners prefer to plant big, leafy mature trees, yet don’t always account for too-narrow plots, ill-advised irrigation and pruning, poor soil quality and roots coiled from spending too much time in small pots.

That’s why a tree species like eucalyptus – brought here in the 1800s for use as railroad lumber – undeservedly gets a bum rap, she said.

“It’s a beautiful tree if allowed to grow peacefully from seeds,” Rivet said. “There are no really bad trees, just bad placement and bad maintenance.”

Yet for all the varied factors that could have played part in San Diego’s recent tree disaster, the most indisputable element was prolonged wind gusts. On Jan. 31, there was a 12-hour stretch of 50 to 60 MPH winds blowing from the coast inland. It took down trees indiscriminately.

Alex Tardy, warning coordination meteorologist for the San Diego office of the National Weather Service, said those in his field consider the “magic number” for wind speed to be 57 miles per hour. That’s when damage is all but inevitable.

“When you see winds like this, it doesn’t matter what kind of tree it is. It’s going to take a beating,” said Tardy.

The Need for Trees

City planners have renewed their commitment to improving San Diego’s tree population. Goals for San Diego’s “urban forest” – government-speak for trees that grow in a city – were outlined in the 2008 General Plan. This month, San Diego was designated as a Tree City USA, a status awarded by the Arbor Day Foundation and the National Association of State Foresters to communities dedicated to trees in public spaces, including a willingness to invest at least $2 per capita to urban forestry.

The city released its draft Urban Forest Management Action Plan on Jan. 15, a working document intended to guide the city’s efforts to inventory, assess and maintain existing trees while making plans to plant more.

Jeremy Barrick, who took on the newly created role of urban forestry program manager for San Diego last August, said the draft plan is working its way through city planners. It could be put before the City Council this May, he said.

One of the biggest jobs of the plan will be to guide how tree data is compiled. Arborists want to know how many trees are here, and how much ground they cover when viewed from above. The last count in 2002 estimated more than 200,000 trees and palms along San Diego’s streets, with an estimated 1 million trees within the city limits, said Barrick. Estimates pegged to aerial and satellite imagery put San Diego’s tree canopy at between 4 and 7 percent.

Ideally, San Diego should have a tree canopy of 35 percent by 2035, Barrick said.

“How realistic is that? It depends on what we currently have. A goal like that starts with the preservation of trees. We won’t be able to plant our way there without preserving what we currently have,” he said.

The California Department of Forestry and Fire Protection, also known as CalFire, has allocated grant money to boost San Diego’s tree population as part of a greenhouse gas reduction program. CalFire has funded the planting and watering of 500 trees citywide over the next three years starting this fall. It has separately funded 300 new trees in Logan Heights alone.

“I hope people understand the benefits of trees and the importance of what it means to properly manage trees in an urban setting,” Barrick said. “A lot of people think that trees are a nicety, but they’re an infrastructure need. Trees are amazing multi-taskers – they clean the air, save energy, improve business, increase property values, reduce crime, reduce storm water runoff, cool the pavement. It’s a pretty low-cost piece of infrastructure.”

Tree San Diego, a nonprofit working to build an online database of San Diego trees, has estimated the economic benefit of the city’s 200,000 trees at $2.8 million in offset water and energy costs, the reduction of greenhouse gas and pollution mitigation.

The trees felled by January’s storm mostly went on to become woodchips, though some city contractors may have milled a few choice pieces of tinder, Barrick said. The city intends to explore better means of repurposing the wood in the future, he said.

What Should We Be Planting?

The occasional big storm shouldn’t dissuade San Diegans from planting trees, but we can certainly do it smarter knowing that sometimes the wind blows, sometimes pests attack a species and sometimes the concrete jungle is just too harsh for certain kinds of trees.

Plant experts often preach the benefits of native species, but that doesn’t always work for planting trees here. San Diego didn’t start as a forest of big trees, Rivet said, but as a landscape of scraggly chaparral and coast live oak. Neither does well in the median strip of a city street.

“When we’re in downtown, that’s not a native environment,” Barrick said. “With concrete and compacted soil, it’s tough for a tree to perform in that condition. If we’re in an open space, of course we prefer natives. But if we can’t do native in an urban setting, we have to look to something that grows well.”

Fortunately, there are hundreds of species of trees from all over the world that can flourish in San Diego’s dry, alkaline soil. Local arborists work from a recommended list of about 150 street trees. The Logan Heights tree-planting project, for example, has a city permit for 10 varieties, from California sycamore to Chinese pistache.

Species diversity is an important aspect of maintaining San Diego’s existing tree canopy. Weather, bugs and disease have been known to take out an entire species in a region.

It’s also worthwhile to be mindful of where trees are planted. Mike Reed, president of the Professional Tree Care Association of San Diego and an arborist for Escondido’s Green Horizons Landscape & Maintenance, said his crews noticed that a lot of the trees downed by January’s storm were planted on slopes.

Reed said he recommends preventative tree maintenance before inclement weather hits.

“We as a public need to maintain our trees and think of the future,” Reed said. “People sometimes say they don’t want the mess, the needles, the seeds. But if we remove our trees we miss out on the value to our property.”

Meteorologists can look to conditions elsewhere to forecast if we’ll have another tree-destroying weather event. The late January storm, for instance, was tracked from south of Japan, Tardy said. While significant rainfall is predicted for San Diego in March, it won’t likely be paired with the same kind of high-sustained winds, he said.

“The reason why we haven’t seen a storm like that for 10 to 15 years, and why we might not for years to come, is the stars have to line up just right,” Tardy said. “It’s still a good reminder for people to be a little more situationally aware. We don’t think of a tree possibly falling, but on those rare days when we’ve issued warning notifications, it’s good to have some type of plan. Spend minimal time near windows, garage your cars, and be aware of what’s around you. And you should be pruning your trees.”

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