What does the pyramid of biomass for a grazing food chain represents?

In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level.So there is gradual decrease in biomass from producers to the tertiary consumers.