A leafy canopy shades about 30 percent of the average American city. But in many cities only one tree is replaced for every four that die.
A leafy canopy shades about 30 percent of the average American city. But in many cities only one tree is replaced for every four that die.
树木的绿色枝叶搭成的天蓬大约遮盖了平均30%的美国城市。但是在许多城市，平均每死掉4棵树，补种的只有1棵。