Gross primary productivity (GPP): It is the rate of production or synthesis of organic matter by producers during photosynthesis per unit time and area. A considerable amount of GPP is utilized by plants in respiration.
Net primary productivity (NPP): Gross primary productivity minus respiration losses (R).
NPP = GPP – R
Net primary productivity is the available biomass for the consumption of heterotrophs i.e., both herbivores and decomposers.