Standing crop biomass divided by net primary productivity.
That is, it is the total amount of primary producer biomass within an environment divided by the amount of new primary producer biomass ( / NPP). The greater the fraction of biomass this is new biomass then the faster the ecosystem must be "turning over", that is, renewing itself.
Note that the biomass of primary producers is depleted particularly by the action of primary consumers. Environments that have high turnover times (e.g., aquatic biomes) consequently can have more biomass associated with than with primary producers as relative to environments which instead have lower turnover times (e.g., terrestrial biomes). These trends can be visualized using .
See by contrast turnover rate, which instead is a property of enzymes