6.1 Net primary productivity
Net Primary Productivity (NPP) is the net amount of energy a plant accumulates during a time period. Because there is a direct relationship between the energy a plant accumulates and the mass of the plant, one can also think of NPP as the amount of mass a plant gains over some period of time (or better yet, how much the plant grows over a given time frame). NPP is calculated by taking the gross primary productivity (the total amount of energy/mass taken in by the plant) and subtracting the plant's respiration (the total amount of energy/mass lost by the plant as it breathes).
By knowing the NPP of a given system, scientists can make predictions about how much carbon dioxide the plant (or on a large scale, region) will pull out of the atmosphere. These predictions can then be used in climate change studies, where people talk about sources or sinks of carbon.
This dataset talks about NPP in units of kg-Carbon per square meter per year, or the net amount of carbon the plants in an average square meter of the gridcell take up during an average year.