The street trees have really four jobs to do and that's it: To spatially denote the pedestrian realm, to protect the pedestrians from the vehicles in the carriageway, to filter the sunlight onto the sidewalk, and to soften the hardscape of the buildings and to create a ceiling -- a vaulted ceiling -- over the street, at its best.
行道树有四项职能，仅此而已： 空间上划出人行道区域 保护好行人不受机动车道上车的影响 过滤照到人行道上的阳光 以及柔化建筑的人造生硬感 最好的话，形成一片天顶——一条街道上方的拱顶