Energy from biomass can be derived from a variety of sources: trees, garbage, sewage plants, waste cooking oil, corn, switch grass,etc.  In other words, like fossil fuels, biomass is composed of hydrocarbons-- but they have not been fossilized.

Pictured right: Dead lodgepole pine, killed by pine-bark beetles, turn the mountains a shade of reddish brown near Granby. (THE DENVER POST | RJ SANGOSTI)