The general interest and attention paid to the use of the renewable natural resources of the world have increased greatly during the last decades. This is due to the environmental dilemma into which mankind has got itself by the total disregard of ecological facts and laws, the underprizing of natural resources and the overemphasis on economic develop ment, coupled with unimpeded rapid population growth and the preponderance of material istic consumption-oriented attitudes. The management and use of natural resources such as forests, grasslands, rivers and lakes were formerly considered...