From forestry: Saplings & Fertilizer are placed in Fermenters to yield biomass which can be used in Biogas engines. It's possible to take Biomass into a Still to yield Biofuel to be used in combustion engines but it's less efficient than refining oil into fuel to be used in combustion engines.
In Forestry 1.0 you could have made a Tree/Peat farm setup that would have mostly self sufficient.
In Forestry 2.0, due to some weird mechanics (possible bug) the default tree farm (managed) produces even more saplings than the Foresty 1.0 tree farms.