Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account.Plants respire all the time, using some of the sugars they make to release energy for active transport, synthesis of molecules and other processes. This energy is eventually lost to the environment as heat. NPP is what is left.NPP is important because it is the energy actually available for:• the plant's own growth and reproduction;
• the other trophic levels in the ecosystem, such as herbivores and decomposers.Like GPP, NPP is usually given as a rate (net primary productivity) in units such as kJ m−2 yr−1.Example: A young, fast-growing forest has a high NPP, because a large proportion of the energy it captures is stored as new wood and leaves. In a mature forest there is far more living tissue respiring, so a larger share of the captured energy is lost in respiration and NPP is lower.NPP is highest where producers are not limited by light, water, carbon dioxide or temperature, for example in tropical rainforests. Deserts have low NPP because of lack of water, and open oceans have low NPP per unit area mainly because of low mineral ion concentrations.Farmers are really interested in NPP rather than GPP, because it is NPP that becomes harvestable crop or food for livestock.
• the other trophic levels in the ecosystem, such as herbivores and decomposers.Like GPP, NPP is usually given as a rate (net primary productivity) in units such as kJ m−2 yr−1.Example: A young, fast-growing forest has a high NPP, because a large proportion of the energy it captures is stored as new wood and leaves. In a mature forest there is far more living tissue respiring, so a larger share of the captured energy is lost in respiration and NPP is lower.NPP is highest where producers are not limited by light, water, carbon dioxide or temperature, for example in tropical rainforests. Deserts have low NPP because of lack of water, and open oceans have low NPP per unit area mainly because of low mineral ion concentrations.Farmers are really interested in NPP rather than GPP, because it is NPP that becomes harvestable crop or food for livestock.