How are the earth's principal biological systems being depleted?

Mr. Lester Brown pronounced in his book, The Global Economic Prospect, that the earth's [roncipal biological systems are four – fisheries, forests, grasslands and crop lands – he called these the foundation of the global economic system. Not just food, all the raw materials for various industries, other than minerals and petroleum-derived synthetics, are provided by these. It is claimed that these systems are reaching an unsustainable level. Those that used to known as renewable sources are now at the verge of becoming non-renewable as their productivity is being impaired. Thus, fisheries collapse, forests disappear, grasslands are converted into barren wastelands and crop lands deteriorate.

Our world is protein-conscious and protein-hungry, this is a great cause for over-fishing every day. In third world nations, local forests are being decimated in order to produce firewood for cooking. One might be astounded to find out that in some places, firewood has become so expensive that what goes under the pot is costlier than what goes inside. Several species now face the threat of extinction due to the destruction of tropical forests, which were called “the powerhouse of evolution” by Dr. Myers.