Which ratio helps compare productivity in different biomes?
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
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 17