The net primary productivity is the biomass that is available for consumers (herbivores and decomposers) for consumption. Respiration is the use of biomass to release energy that can be used to do work. It returns to the environment the carbon dioxide that had been removed by photosynthesis. In respiration, an organic compound is combined with oxygen to release energy and produce carbon dioxide and water. Thus, when the carbon lost by respiration (R) is deducted from the GPP, we obtain a measure called NPP NPP = GPP - R where, NPP is the net productivity; GPP is the gross primary productivity and R is respiration