Cubic Rot - caused by diverse wood-rotting fungi
Fungi are the best wood rotters in the natural world. Breaking down lignin and lignified cellulose is the primary role of a large number of forest fungi. Many wood rotting fungi attack the wood at the lines of weakness such as the vascular rays and the junctions of the annual rings. As it is decomposed and dries out the wood cleaves along these lines. Small sections of the circumference give the illusion of a straight line and the pieces of wood appear to have broken at right angles, hence the term "Cubic Rot".