Biomass production at all trophic levels is ultimately dependent on the quantity and quality of resources comprising the basal trophic level. Experimental manipulations have generally found that biomass at all trophic levels increases with increased NPP. The ecosystem-level importance of bottom-up control is further underlined by the fact that global patterns of NPP correspond generally to predictions generated by models using only data on abiotic factors such as light, temperature, and water availability. There are also many systems, however, where top-down control clearly acts as a regulatory force; when unchecked by natural enemies, herbivores are capable of population outbreaks that can devastate producer biomass. In agricultural systems, the biological control of crop pests is predicated on the ability of natural enemies to suppress herbivore abundance, reduce producer damage, and increase overall yield. Given that bottom-up control is essential to determining biomass production, the critical issue becomes understanding the conditions and systems in which top-down processes are also important. The open access journals are peer reviewed scholarly journals of Biochemical engineering. The top open access Biochemical engineering journals are freely available on the public internet domain, allowing any end users to read, download, copy, distribute, prink, search or link to the full texts of the articles.