So, forests and plants are the most important sources of food for man. In the tropics, of which Thailand is a part, forests and plants not only provide watersheds but are also the largest source of of oxygen. Compared to a human body, forest is the lung. Apart from keeping the earth's climate 'balanced', forest also controls the flow of water year round. This is reason why denuded areas suffer more severely from floods.
Rivers are arteries that feed all living things.
Many fertile rivers are in the tropics that encompasses major world civilizations. In the rainy season, rivers overflow their banks and deposit silt or natural fertilizer from watershed areas to river basins enriching the soil. Plants and aquatic life, such as fish, are important protein sources and provide income for the world's population. If man know how to use them wisely, these large kitchens of the world would be able to sustain him forever. The fact that man dissociated himself from the ecosystem recently, through industrial revolution, over exploitation of natural resources has resulted in the destruction of our ecosystem.