Woodpeckers excavate nest cavities in trees with soft interior wood (Lorenz et. al., 2015). By degrading lignin and cellulose, wood-rotting fungi decrease wood density in potential nesting trees, decreasing excavation time for woodpeckers (Jackson and Jackson, 2004). Cellulose must be broken down into single glucose molecules for fungal metabolism by a variety of cellulases. Cellobiose, a product of cellulose digestion, is hydrolyzed to two glucose molecules by cellulobiase (β-glucosidase). We measured fungal cellobiase activity in wood from woodpecker nest trees and control (non-nest) trees using a p-nitrophenol glucopyranoside enzyme assay. The breakdown of p-nitrophenyl glucopyranoside by cellulobiase in extracts from the wood samples released p-nitrophenol. We measured absorbance of the resulting solution to determine cellulobiase activity. Because woodpeckers excavate in trees that are less dense than random control trees in forests of Eastern Washington (Lorenz, et. al., 2015), we predicted that cellulobiase activity would be higher in nest trees than in random control trees.
Samples from nest trees had higher total cellulobiase activity than control trees after 24 hours of incubation (p=0.025) and total cellulobiase activity had an inverse relationship with wood density: higher activity was associated with lower wood density (p<0.026 ). Cellulobiase activity may be a good indicator of whether a tree or snag would be suitable for cavity excavation by woodpeckers.