GPP is the rate at which biomass or organic matter is produced by producers during photosynthesis per unit area over a time period. It is expressed in terms of weight as or energy to compare the productivity of different ecosystems. Net Primary Productivity (NPP): It is defined as gross primary productivity minus respiratory loss (R).
NPP = GPP - R
Net primary productivity is the available biomass for the consumption of heterotrophs i.e., both herbivores and decomposers. Secondary productivity: It is the rate of formation of organic matter by consumers.