Introduction : What is the relationship between production of agricultural and non-agricultural vegetation ? Bioman pools and primary productivity of natural and managed ecosystem types in a global perspective. The capacity of the World Land Area to produce agricultural products. Environmental contraints on productivity of the mediterranean selerophyll shrub Quercus coccifera. To what extent can agricultural production be expanded ? Primary production in agroeocystems. Net primary productions, net ecosystem production and nutrient availability. The effect of interlevel hierarchical system communication on agricultural system input-output relationships. Energy flows in agricultural and natural ecosystems. Input-output relationsphips on North China collective farms. The contribution of external inputs and intrinsec state conditions to agroecosystems productivity. Summary of the main arguments form a theoritical perspective.