Which productivity measure indicates the biomass produced by primary producers that is available for consumption by herbivores?

The measure that indicates the biomass produced by primary producers available for consumption by herbivores is net primary productivity (NPP). This is calculated by taking gross primary productivity (GPP), which is the total amount of biomass produced through photosynthesis, and subtracting the biomass that is used by primary producers for their metabolic processes, primarily through respiration.

Essentially, NPP represents the energy or biomass that is stored in plant tissue and can be transferred to herbivores when they consume these plants. Therefore, NPP reflects the actual energy available to the next trophic level, which is crucial for understanding ecosystem dynamics and energy flow. Gross primary productivity represents the overall production but does not account for the energy lost to metabolic activities of the primary producers, while net secondary productivity is concerned with the biomass produced by consumers after accounting for their own metabolic processes.