Forest trees are not just sources of building material and paper pulp but are also sys­tems for carbon dioxide sequestration and a source of biofuel. It is proposed that genetic manipulation could increase carbon partition to woody tissues, and increasing cellulose availability for digestion. Lignin content can be changed by modification of gene expression (Groover, 2007). Plant material having less lignin is more digestible when lignocellulose needs to be broken down into sugars for ethanol production. Reduction in lignin content has been achieved in trees in order to reduce the bleaching required when making paper pulp. Changes in lignin content have been carried out in maize, sorghum, poplar and pine (Gressel, 2008). Some concerns have been aired that a reduction in lignin content will weaken plants, causing flattening of crops (lodging), but the evidence for this is limited as many of the crops used now are short stemmed.