Trees are useful to man in three very important ways：they provide him wood and other products;they give him shade;and they help to prevent drought(干旱)and floods.

　　Unfortunately，in many parts of the world，man has not realized that the third of these services is the most important.In his eagerness to draw quick profit from the trees，he has cut them down in large numbers Two thousand years ago，a rich and powerful country cut down its trees to build warships，with which to gain itself an empire It gained the empire but，without its trees，its soil became bare and poor.When the empire fell to pieces，the country found itself faced by floods and starvation.

　　Even where a government realizes the importance of a plentiful supply of trees，it is difficult sometimes to make the people realize this.They cut down the trees but are too careless to plant and look after new trees So，unless the government has a good system of control，or can educate the people，the forests slowly disappear

　　This does not only mean that there will be fewer trees.The results are even more serious：for where

　　there are trees，their roots break the soil up，allowing the rain to sink in， and also bind the soil.This prevents the soil from being washed away.But where there are no trees，the rainfalls on hard ground and flows away on the surface，and this causes floods and the rain carries away the rich topsoil in which crops grow When a11 the topsoil is gone.nothing remains but worthless desert.

　树木对于人来说有3个重要益处：树木给人类提供木材和其他产物;树木可以让人们乘凉;树木可有效地防止旱涝灾害。

　　可惜的是，在世界上许多地方，人类没有认识到以上三个作用中，第三个是最重要的。人们急切于从树木上快速的谋取利益，于是大量的砍伐森林。

　　两千年之前，有一个富裕和强大的国家。为了建立帝国，砍倒了树木来造战舰。帝国建立了，但是，没有树木的土地变得荒芜和贫瘠。当帝国四分五裂的时候，整个国家发觉自己面临的是水灾和饥荒。 就算在政府认识到足够的树木储备的重要性时，有时却很难让人民也意识到这点。人们砍倒了树木，却疏于种植和照料树苗。因此，除非政府建立一套体制来控制或者教育人们，否则森林就会渐渐消失。

　　森林的消失不仅仅意味着树木的减少，还有更严重的后果。在有树的地方，树根不仅把土壤粉碎成小块，便于雨水的渗入，还可以牢牢的抓住泥土，防止泥土被冲刷走。但是在没有书的地方，雨水直接落在坚硬的地面，在土地表面流走。这不仅会导致洪水，雨水还会带走庄稼赖于生长的肥沃的表层土。当所有的表层土被冲走之后，除了毫无价值的沙漠之外，什么也没有了。