The “after” images in my recent proposal to narrow a residential street such as McAllister didn’t emphasize any street trees or other greenery. The general lack of greenery was one of the more common issues raised, even among many supporters of the broader narrow streets proposal.
Of course, plants of all kinds certainly play a role in making a street more pleasant and livable, and there’s no reason they can’t be incorporated into a narrow street. The key is to use them as a way to embellish a properly sized Street For People, not to serve as filler on an excessively wide street.
In real world examples it’s common to see a simple arrangement of potted plants, placed in front of a house or business and cared for by the occupants.
Trees show up occasionally, both in smaller urban villages and larger cities like Paris. They tend not to be as massive as some of the trees we see in San Francisco today, which the city struggles to care for, and which have an unfortunate tendency to fall and cause damage.
Some of the best streets use a mix of everything — hanging or potted plants, flower boxes, bushes, trees. It’s really up to the residents of the street to choose what they want and what they’re willing to maintain. Interestingly, smaller streets often seem to encourage a greater sense of care and ownership among residents. And with fewer big trees, there can be less of a public safety need for the city to get involved in trimming and maintenance.