20世纪末,美国西部一个州的一场森林大火,使上万亩森林遭灾。事后,人们发现罪魁祸首是森林中的那些枯枝朽叶。于是,州政府对森林中枯萎、干枯的树木、草叶进行了清理,以杜绝隐患。在随后的两年里,再没有大的火灾发生,但一种由云杉卷叶蛾引起的虫害,大面积地暴发了。美国农业部 At the end of the twentieth century, a forest fire in one of the western states hit the forest by 10,000 mu. Later, people found that the culprit is those dead branches in the forest. As a result, the state government withered, withered trees and grass leaves in the forest were cleaned up to eliminate hidden dangers. In the ensuing two years there was no major fire, but a large pest outbreak caused by a spruce-leaf moth. U.S. Department of Agriculture