[慢速VOA] 防风林保护庄稼(2)[080804]
Building a Windbreak to Protect Crops (2/2)
For this reason, a windbreak is best if it has only sixty to eighty percent of the trees and plants needed to make a solid line. An easy rule to remember is that windbreaks can protect areas up to ten times the height of the tallest trees in the windbreak.
There should be at least two lines in each windbreak. One line should be large trees. The second line, right next to it, can be shorter trees and other plants with leaves. Locally grown trees and plants are best for windbreaks.
If the quality of the land is not very good, studies have shown that one kind of tree that can grow well is the white pine. Another is the loblolly pine. Windbreaks not only protect land and crops from the wind. Surplus trees can be cut down and used to provide wood.
Trees reduce the damaging effects of wind and rain. Their roots help protect soil from being washed away. And trees do something else -- they can provide grazing animals with shade from the sun.
