Biodiversity means the living organisms themselves and the diversity and variability of the ecological complex which living organisms depend on for their survival. We may realize it and arrange it both macroscopically and microscopically into 5 levels, namely：ecosystem diversity, association diversiity, species diversitiy, cytological diversity and genetic diversity. Biological resources are the material expression of biodiversity and the material things are evaluated to supply food, medicine, raw and processed materials for industry and energy resources for the existence of mankind and the develo pment of national economy. Yet, the living things, including plants, animals, microbes and human beings, together with their environment, i.e., the atmosphere, water and soil, form an interdependent and interacted circulatory system （the ecosystem ） in the biosphere. Nowadays every ecological problem is closely related to human ecology. Whether human as a coordinator in the ecosystem, or as a destroyer depends on what strategy they adopt and what kinds of ecological processes of exploitation and utilization they choose. Therefore the rational utilization and protection of plants should become the key of solving problems of the six ecological crises. These crises we are facing are the consumption of energy, the exhaustion of resources, the explosion of population, the shortage of food and water, the degradation of environment and the imbalance of ecological circulation. From the past geological ep ochs up to the present, no green plants （especially higher green plants） means no any other living things and no human society, and any irrational cleeaning of plant covers on the earth would lead to an ever worsening condition of our environment, and thus cause the six ecological crises successively or simultaneously and seriously, which would result in the extinction of quite many biological species, even including Homo sapiens itself. The only way of preventing the degradation lies on the rational use of plants. The degree of the compromise attained between mankind and plant kingdom may be a measurement of rationalization. We believe that modern agriculture is the common goal. In this ＂Great Agriculture＇, ecology and economy are combined togetther, and as many as we can use the multifarious biological resources from different levels of biodiversity. However, their nucleus is agro-forestry, being an ecological arrangment of several kinds of regenerable resources from various biodiversities, with resources in the form of agriculture and forestry playing the major role. The rational measure will be gradually formed during the full application of every kind of modern and scientific means for cultivation.