In Mold, Housing and Wood, wood products experts at the Western Wood Products Association write:
Fungi evolved over 400 million years ago (Sherwood-Pike, 1985) and references to mold in buildings suggest that molds have always been present in human environments. At present there is growing public concern about the potential health effects of mold in homes and structures that has been heightened by media reports and litigation.
There are a host of materials in and around the home that, under proper conditions, can become breeding grounds for mold. Molds can grow on organic materials such as drywall paper, wood panels, lumber and carpet backing. They may grow equally well on inorganic materials such as concrete, glass or plastics that may have nutrients on the surface. In all cases, the presence of moisture is a critical condition for the growth of mold.
Lumber is an organic material. In situations with adequate moisture, mold can become established on wood. However, in all cases involving mold, the underlying problems such as flooding or water leaks affect many materials in the structure, including lumber.