城市里有防护林存在的必要吗?有,它们不但有防风作用,还有消音、遮荫、净化空气和疏导交通流量等作用。由于许多居民和团体认识到防护林为城市提供的这些利益,他们正在城市里栽植成行的树木。最常栽植的是单行防护林。每行树木可由铅笔柏或落基山桧组成;也可由阔叶树和 Are there any shelterbelt in the city? Yes, they not only have the function of wind-proof, but also silence, shade, purify air and divert traffic flow. As many residents and groups recognize the benefits that shelter offers to cities, they are planting trees in the city. The most common planting is a single shelter. Each row of trees can be composed of Penaeus or Rocky Mountain cypress; also by the broad-leaved trees and