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How can fungi discolor or decay wood after a tree is cut down?

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temperate softwoods and hardwoods selected to show variations — wood Temperate softwoods (left column) and hardwoods (right column), selected to highlight natural variations in colour and figure: (A) Douglas fir, (B) sugar pine, (C) redwood, (D) white oak, (E) American sycamore, and (F) black cherry. Each image shows (from left to right) transverse, radial, and tangential surfaces. Click on an individual image for an enlarged view.

Fungi can cause discoloration or decay in wood after a tree is felled, provided that environmental conditions—specifically moisture, air, and temperature—are suitable for their growth and activity.1

Discoloration (Stain)

Stain fungi primarily affect the aesthetic quality of wood, often causing a significant reduction in market value. A common example is blue stain (or sap stain) in pines, which turns the sapwood bluish or blackish in wedge-shaped patches. This process can occur rapidly, sometimes within hours or days of the tree being cut or processed, particularly in warm weather.1

Decay

Decay fungi are the most significant cause of wood loss. Their growth is inhibited if the wood's moisture content drops below 20 percent or if temperatures fall outside the range of 10–30 °C (50–86 °F). Additionally, wood submerged in water is protected from fungal attack due to the lack of sufficient oxygen. While some wood species possess natural resistance due to toxic extractives, no wood is entirely immune to these organisms.1