Practice question

The ratio NPP/biomass compares how much new producer material an ecosystem generates relative to its existing standing biomass during a specified time. It is closely related to production-to-biomass ratio and biomass turnover rate. A grassland may have modest standing biomass yet replace a large fraction annually, producing a high ratio, whereas a mature forest stores enormous amounts of wood but adds a smaller fraction each year, producing a lower ratio. Normalizing production by biomass therefore enables comparison among biomes that differ greatly in size and growth form. NPP alone measures absolute net production per area and time; biomass alone measures the stock, not its renewal. Leaf area index helps explain light interception but does not directly express whole-ecosystem productivity relative to stock. Respiration per CO2 is not a standard biome productivity ratio. Care is needed to use matching units, spatial boundaries, and time intervals. Mechanistically, NPP/biomass indicates how rapidly the producer carbon pool turns over, linking ecosystem productivity to the amount of living material that generates it.