The productivity(or production) of an ecosystem is the amount of biomass produced by that ecosystem each year.
- Productivity can be measured in units of biomass (e.g. kg m-2 y-1), or units of energy (e.g. MJ m-2 y-1).
- We can measure the amount of plant biomass produced (primary productivity), or the amount of consumer biomass produced (secondary productivity).
- The amount of energy fixed by producers in photosynthesis and stored as chemical energy in glucose is called the gross primary productivity(GPP), while the amount of energy absorbed by consumers is called the gross secondary productivity(GSP).
- Some of this gross productivity is lost as heat (via respiration) and so is not available to the next level in the food chain.
- The amount of energy actually accumulated in producer or consumer biomass, and available to be passed on to the next trophic level, is called the net primary productivity(NPP) or net secondary productivity (NSP) respectively.
- Gross and net productivity are related by this equation:
Net productivity = Gross productivity – Losses due to respiration and heat
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