Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores and decomposers).

• Nature tends to increase the gross primary productivity so that it can utilise much of the solar energy and convert it into food.
• Man tends to increase the net primary productivity so that sufficient food is provided to the growing human population.