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In our four-plus decades of planting and caring for street trees in San Francisco, we've heard a lot of myths and misconceptions. Here are a few of the most common... along with the relevant facts you need to know.
MYTH: IF IT’S BY MY HOUSE, IT’S MY TREE
It’s easy to understand why the sidewalk in front of a house seems to “belong” to that house and its owner. After all, the property owner is legally required to maintain that portion of the sidewalk in good repair and condition. But the city owns the sidewalk and the trees planted in it — even if the adjacent property owner chose the species and planted it. The good news is that San Francisco Public Works is responsible for maintaining street trees and repairing tree-related sidewalk damage — not the property owner. This is thanks to a voter-approved initiative that Friends of the Urban Forest helped pass in 2016, which requires the city to allocate sufficient funds for that purpose. Read more about the city’s street tree maintenance program here.
MYTH: TREE ROOTS RUN DEEP
Do you envision that a tree’s root system is like a deep, mirror image of its branches? Actually, roots usually stay pretty close to the surface – the roots of most of the trees we plant are within 12 inches of the soil surface. But they can spread out wider than the tree is high. That’s why Friends of the Urban Forest cuts basins (rectangular holes in the sidewalk) as large as possible (and legally permissible) when we plant trees.
MYTH: TREE ROOTS BREAK SEWER LINES
Friends of the Urban Forest and utility companies collaborate on identifying sites where trees can be planted without interfering with existing above- and underground utilities, including sewer laterals (the pipes that connect homes and other buildings to the municipal sewer line under the street). City code requires a minimum of 5’ of clearance between a tree and a sewer lateral. Tree roots don’t break into intact pipes. However, they’re attracted to moisture, and they may indeed grow into a cracked or broken pipe that’s leaking water — and then cause further damage to the pipe. Older sewer laterals were often made of clay, which cracks more easily than newer plastic or metal pipes. Therefore, property owners with trees located near old sewer laterals may be able to avoid problems by checking for cracks and leaks. See this page from the San Francisco Public Utilities Commission with tips for keeping sewer laterals in good condition.
MYTH: A STREET TREE'S JOB IS JUST TO LOOK PRETTY AND PROVIDE SHADE
We agree with anyone who admires the beauty of trees — and it’s true that by providing shade they perform a vital service. Did you know that San Francisco is the third-fastest-warming city in California? A study from American University showed that neighborhoods with over 50% tree canopy coverage are significantly cooler than those without. That's why a robust urban tree canopy can help us survive a warming planet. But street trees do SO much more than that! They fight climate change by storing carbon, and they produce oxygen, reduce pressure on our storm/sewer system by capturing rainwater, provide habitat for wildlife, calm traffic, dampen noise, and relieve stress. Read more about these benefits here. Thanks, trees!
MYTH: A TREE'S BRANCHES RISE AS IT GROWS
Consider a newly planted, six-foot-tall street tree that has lower branches just four feet off the ground. Years from now, when the tree has tripled in height, do you imagine that those lower branches will have risen along with the tree, perhaps out of reach? Nope. They’ll get thicker but they’ll stay roughly where they are as the trunk rises and more branches form above them. That’s why our Tree Care Team does structural pruning during the tree’s “establishment period” to ensure that the tree has a good, sound form, including appropriate clearance for vehicles and pedestrians.