Which fungi might contribute to the structural weakening of wood?

Wood decay fungi are the primary organisms responsible for the structural weakening of wood. These fungi break down the cellulose and lignin in wood, which are the key components that give wood its strength and stiffness. As wood decay fungi metabolize these materials, they not only lead to a reduction in the integrity and durability of the wood but can also create visible signs of decay, such as discoloration and softening of the wood.

In contrast, blue mold and sap stain fungi primarily affect the aesthetic quality of wood rather than its structural properties. Blue mold typically causes a bluish stain on the wood surface, and sap stain fungi discolor the wood but do not contribute to its degradation. Non-decay fungi, as the name suggests, do not cause decay in wood at all. They may exist alongside decay fungi but do not contribute to the weakening of the structural integrity of wood. Therefore, when considering which category of fungi poses a risk to the strength of wood, wood decay fungi is the clear choice, as they fundamentally alter the wood's composition and structural soundness.