Bioproductivity

Bioproductivity is the rate at which living organisms produce biomass, giving a measure of how efficiently ecosystems convert energy into organic matter. In ecological studies it usually refers to primary productivity, the production by photoautotrophs like plants, algae, and cyanobacteria. Bioproductivity can be described at different levels: gross primary productivity (GPP) and net primary productivity (NPP). GPP is the total amount of carbon fixed by photosynthesis per unit area per time; NPP is the portion remaining after plant respiration, available to promote growth and to support heterotrophs. Secondary productivity refers to biomass produced by consumers.

Measurements: GPP and NPP can be measured directly by harvest-based methods for local plots or indirectly via respiration measurements, or inferred from eddy covariance flux towers, which estimate ecosystem-scale CO2 exchange. Remote sensing using satellite data and indices such as NDVI and EVI approximate GPP over large areas. Units include grams of biomass per square meter per year (g m^-2 yr^-1) or energy terms (kcal m^-2 yr^-1). Temporal scales range from seasonal to interannual and longer.

Variation and controls: Productivity is influenced by light, temperature, water availability, nutrients (especially nitrogen and phosphorus), and disturbances such as fire and grazing. Tropical forests and algal blooms often show high production; deserts and tundra show low productivity. In oceans, marine productivity is patchy and often limited by nutrients rather than light, with phytoplankton driving much of the GPP.

Significance: Bioproductivity is a central component of the carbon cycle and climate models, affecting atmospheric CO2 levels. It informs agricultural planning, forest management, and restoration. Limitations include methodological uncertainties and differences between measurement approaches.