San Francisco is the unusual case among large American cities: it had almost no tree cover to begin with. The peninsula was sand dune, coastal scrub and grassland, so essentially the entire urban forest is planted, and almost all of it is exotic. Species that thrive here were chosen for tolerance of cool summers, salt-laden wind and near-permanent fog on the western side, which is why the palette leans so heavily on Monterey cypress, Monterey pine, New Zealand Christmas tree and Victorian box rather than the oaks and maples common elsewhere.
Permitting is stricter than anywhere else in the region and catches people out. A permit from Public Works is required to remove any street tree, meaning any tree in the public right-of-way. Beyond that, a tree on private property counts as significant — and also needs a permit — if any part of its trunk is within ten feet of the public right-of-way and it exceeds one of three thresholds: a foot in diameter at breast height, twenty feet in height, or fifteen feet of canopy width. Landmark trees designated by the Board of Supervisors have further protection. Replacement or an in-lieu fee is normally required.
Much of the city's Monterey cypress and pine was planted in the same era and is now ageing together, which is a maintenance problem arriving all at once.
Tree service questions in San Francisco
- Do I need a permit to remove a tree in San Francisco?
- Almost certainly, and more often than owners expect. Every street tree — any tree in the public right-of-way — requires a Public Works removal permit. A tree on private property also requires one if it qualifies as significant. Landmark trees have additional protection and are difficult to remove at all. Replacement planting or an in-lieu fee is generally a condition of approval. Check before any work is scheduled; unpermitted removal is expensive.
- What makes a private tree significant here?
- Two things together. Any portion of the trunk must be within ten feet of the public right-of-way, and the tree must exceed at least one of three measures: over one foot in diameter at breast height, over twenty feet tall, or a canopy more than fifteen feet across. A large tree at the back of a deep lot generally falls outside the definition; the same tree near the pavement does not.
- Why do so many trees here look wind-sheared and one-sided?
- Persistent onshore wind off the Pacific, carrying salt. Growth on the exposed windward face is repeatedly damaged and buds die back, so the crown develops asymmetrically downwind. It is a normal response to the site rather than a defect, and pruning to even the crown up cosmetically usually makes the tree less stable, not more.
- Why is so much of the Monterey cypress in poor condition?
- Age, largely. Big plantings went in across the city and its parks within a relatively narrow window, so a very large cohort is reaching the end of its reasonable lifespan at more or less the same time. Monterey cypress is also naturally short-lived away from its small native range on the Monterey Peninsula. Decline across a whole stand is usually the cohort ageing rather than an outbreak of anything.