Net Primary Productivity

Net primary productivity (NPP) tells you how much new plant biomass is actually added after producers use some of the sugars they made for their own respiration. Plants capture energy from sunlight by photosynthesis, but not all of that captured energy becomes stored growth: some is immediately spent on maintaining cells, repairing tissues, and other life processes. Because of that, subtracting respiration from gross primary productivity gives the amount of energy left for plant growth and for the rest of the food web.

Use this formula when comparing how productive different ecosystems are, such as forests, grasslands, lakes, or crops. It is also useful for estimating how much biomass is available for herbivores and decomposers in an ecosystem.

• Adding respiration instead of subtracting it
• Confusing NPP with GPP, which is the total energy captured before respiration
• Forgetting to keep the units consistent, such as using g C/m^2/year throughout