Currently, the aims of a biomass studies are to elucidate energy and nutrient cycles. The available data concerning biomass and nutrients mostly refer to conifers and a few other major commercial hardwood species, while little information exists regarding other less important forest species of scant commercial value. Furthermore, the information concerning forest biomass is obtained from inventories where only the commercial volume of biomass is taken into account and hence the total biomass is underestimated and other fractions, such as branches and leaves - useful when size and shape is not important - are not considered. Such studies are also used to observe the effect of the vegetation on the global CO2 cycle. Some CO2 models include the estimation of biomass as the volume, its components, or some related parameters in order to establish the flows of gas between the vegetation, soil, and the atmosphere.