Biomass energy, from plants, is a rich source of carbon and hydrogen, and one that can be used within the natural carbon cycle. Fast-growing plants, such as switchgrass and willow and poplar trees, can be harvested as "power crops." Biomass wastes, including forest residues, lumber and paper mill waste, crop wastes, garbage, and landfill and sewage gas, can be used to produce heat, transportation fuels, and electricity, while at the same time reducing environmental burdens.