Street Science: The Mission’s Trees

Some of the Mission District’s oldest residents may also be the most overlooked. Originating from Eastern Siberia, Australia, Southeastern Europe and the Southern region of the United States, some are more than 100 years old and have been in the neighborhood for years. Yet you probably know very little about their history because these locals aren’t people, they’re trees.

Trees give the Mission its look and feel. Imagine 24th Street without its ficus trees, which provide shade, drop crunchy fruits on the ground and break up sidewalks (for a previous Mission Local article on these trees go here). Likewise, picture Dolores park without its slackline-wrapped palm trees, the South end of Folsom Street without its tall elms, or the neighborhood in the Spring without its brightly colored bottlebrush trees and cherry blossoms.

These non-native trees that provide shade, color, and oxygen to the neighborhood are now a big part of the urban forest, and have their own histories of residency and migration within the Mission.

So, how did they get here, and why did they come?

There are at least 6,859 trees planted in public spaces in the Mission, according to Urban Forest Map, a collaboration of groups that’s mapping trees in San Francisco. In a place that was once bare of trees, that’s now about one tree for every seven people.

“Most trees now are planted by Friends of the Urban Forest in collaboration with the City,” said Kelaine Vargas, project lead for the Urban Forest Map.

“Their choices are restricted by what will grow well in such an urban setting, what’s available, what people are interested in seeing on the streets, and years of experience about what works well and what doesn’t,” she said.

The Department of Public Works (DPW) has jurisdiction over all public trees, and is charged with planning, planting, maintenance and removal. In 2011, however, maintenance responsibilities of 23,700 street trees in San Francisco were transferred to property owners due to budget cuts, according to a DPW report. It will take time to see what the results of this are, said Doug Wildman, Program Director of Friends of the Urban Forest (FUF).

“The Department of Public Works, Friends of the Urban Forest, neighborhood groups, individuals, community gardeners and arborists all work to maintain street trees.  There are a lot of partnerships between individuals and cities, and also with parks and rec within the parks,” said Amber Hasselbring of the Mission Greenbelt Project.

To help decide what trees should be planted in selected areas of the neighborhood, the department lists guidelines which encourages climate-appropriate trees. Straight columnar trees are better for narrow streets and trees with overarching canopies are a better fit for wider, mixed-use boulevards. These rules can dictate what the landscape looks like.

“Whatever species are planted has also depended on their performance over time. They work well, and they’re tried and true,” said Wildman.

“Throughout the whole city, trees are selected if they’re good for the sidewalk, clean, longer lived, if the leaves keep in the winter, or for their environmental services like absorbing pollutants,” he added.

Some trees once considered ideal are now causing problems

Let’s look at the ficus trees on 24th Street again, for example. Although they were favored in the 1980s, they have generally not been planted since then because the surface roots cause sidewalk damage, and the city is losing many of them to an apparent fungal disease, perhaps moving in from root pruning activities. Nowadays, if a developer wants to plant a ficus tree, the city tends to shut down the request.

“But they’re great canopy trees, and they’re evergreens, so their leaves act as sponges, absorbing water and delaying a ton of storm water from running off into drains and causing floods,” said Wildman.

For these reasons, planners must have seen them as being beneficial for the city and planted a large number of them at one time. “They were the ‘ideal’ tree of the day,” Wildman said.

Many species are refused for some characteristic or another, allowing for only a select number of tree species to be planted. One city ordinance, for example, advises against planting fruit-bearing trees on streets, because the city doesn’t want trees to drop fruits on people, sidewalks or cars.

“This means that most of the trees planted are male, and therefore there’s a lot of pollen in the air here,” said Hasselbring.

Diversity is key

There can be problems if there’s a lack of diversity among trees, though.

“We can’t have too many of one species in an area or they could be wiped out by a disease,” said Wildman, “so it’s important to reduce large plantings of the same type.”

Nevertheless, a number of the ones that now live in the Mission seem to come in packs, as the map above displays. Toggle the legend to see that most palms were planted along Mission and Dolores Streets, most ficus trees were planted along 24th Street and Potrero Avenue, and most elms were planted towards the Southern end of Folsom Street.

Generally city planners love to have blocks of the same tree, Wildman commented, to define a given section of the city or a district. Friends of the Urban Forest tries to counter that, though, by continuing to request at least two tree species on a given block to prevent wiping out a single population of trees.

A guide to the trees around you

There are no native trees planted in the streets because most natives – like oaks, willows, and toyons – don’t have an upright, columnar form. They grow well if they have significant growing space, which city streets don’t tend to allow for.

Highlighted below are some of the most common street trees — along with a couple others that tend to stand out for their eye-catching flowers, fruits or bark — that define the Mission’s current urban forest landscape, starting with the most abundant species. The species mapped above and listed below by no means account for all the tree species of the Mission.

For a more thorough list, visit the Urban Forest Map website.
Brisbane Box, Vinegar Tree (Lophostemon Confertus)
Tree Count (in the Mission): 480
First Planted in the Mission: It’s been planted in the last 15 years or so, because it’s one of the few “well behaved” tall evergreen trees; there are no pests and diseases yet.
Native to: Australia.

Cherry Plum (Prunus Cerasifera)
Tree Count: 398
First Planted in the Mission: It’s been planted in the last 30+ years, but they’re short lived to 25 years or so.
Native to: Southeastern Europe or southwestern Asia.

Indian Laurel Fig, Chinese Banyan (Ficus Microcarpa Nitida)
Tree Count: 386
First Planted in the Mission: Planted heavily in the 1980s.
Native to: India, Malaysia.

Mexican Fan Palm and Canary Island Date Palm (Washingtonia Robusta and Phoenix Canariensis)
Tree Count: 306
First Planted in the Mission: Just after the 1906 earthquake.
Native to: The desert mountain valleys and canyons of Sonora and Baja Mexico.

Southern Magnolia (Magnolia Grandiflora)
Tree Count: 304
First Planted in the Mission: These have been in the Mission for a very long time because they’re good performers throughout the warmer parts of SF. There are very old, large specimens around Dolores Park.
Native to: Southeastern United States

Jacaranda (Jacaranda Mimosifolia)
Tree Count: 241
First Planted in the Mission: Unknown
Native to: Brazil, Argentina

Siberian Elm, Chinese Elm (Ulmus Pumila, Ulmus Parviflora)
Tree Count: 203
First Planted in the Mission: Unknown. One reason they were originally planted was because they were fast growing, but with that comes more frequent tree pruning.
Native to: China, Japan, North Korea, Eastern Siberia

Bottlebrush, New Zealand Christmas Tree (Melaleuca Spp., Callistemon)
Tree Count: 146
First Planted in the Mission: Unknown. They were originally planted because they’re good performers and relatively “clean” trees.
Native to: Australia

Ginkgo, Maidenhair Tree (Ginkgo Biloba)
Tree Count: 133
First Planted in the Mission: Unknown. These are long lived trees with no pests and diseases. Ginkgo Biloba is also one of the oldest tree species on earth.
Native to: Eastern China

Strawberry Tree (Arbutus Marina, Arbutus Unedo)
Tree Count: 113
First Planted in the Mission: Unknown
Native to: Not precisely known. Some say the Mediterranean, Western Europe, and the Pacific Northwest.

New trees being planted in the Mission:

Chilean Soap Bark (Quillaja saponaria)

Japanese Blueberry (Eliocarpus decipens)

Coast Banksia (Banksia Integrifolia)

Red Horse Chestnut (Aesculus Carnea)