Extreme chemical or biological degradation leads to physical degradation, i.e., loss of the artifact. Wood can be degraded by fungi or bacteria. Fungal degradation can be divided into brown rot fungi (BRF), white rot fungi (WRF), and soft rot fungi (SRF). WRF, which mainly affects hardwoods such as oak, can degrade all the components of wood (lignin, and the polysaccharides hemicellulose and cellulose) but may be selective in which components it removes. BRF mostly affect softwoods and mostly degrade the polysaccharides with only minor alteration of the lignin. BRF act through dealkylation, demethylation and demethoxylation, but do not degrade the aromatic rings. SRF are generally common in waterlogged and aquatic environments and, similarly to BRF, mostly degrade the polysaccharides, with only minor alteration of the lignin.