name the principle biological system of the earth ? why are they all important .

The principal biological systems of the earth are four in number-fisheries, forests, grasslands and croplands or agricultural lands-which are the fundamental components of the global economic system. Their importance stems from the fact that in addition to supplying our food, these four systems are the main suppliers of all the raw materials for industry except minerals and petroleum derived synthetics. In large areas of the world, human claims on these systems have reached an unsustainable level, a point where productivity can be impaired. If this happens then fisheries will collapse, forests disappear, grasslands will be converted into barren wastelands and croplands will deteriorate. This would destroy the fine thread by which ecological balance hangs.