A lumber mill is a primary Industries that only appers in the Climates. It produces Wood which should be delivered to a Factory, but does not accept any cargo.
Lumber mills are a special industry that are not generated automatically but can only be funded by the player. They can only be built in rainforests where they will cut down trees in the surrounding area. Once all trees in this area are chopped down, production will drop to 0. As a result, some manual tree-planting may be required to sustain this industry.