The efficacy of fungal inoculation of live trees to create wood decay and wildlife-use trees in managed forests of western Washington, USA

Abstract Decaying wood plays a vital role in maintaining biological diversity and ecological processes within forest ecosystems. One enhancement that may help to maintain wood-decay processes in managed forests involves the inoculation of healthy trees with fungus to create potential habitat trees to enable excavation for foraging and nesting by primary cavity nesters (i.e., woodpeckers); however, this approach has only received limited evaluation. We evaluated the inoculation of Fomitopsis pinicola into live trees in managed forests in western Washington in 1997 and 1998. In 2006, we revisited trees that were inoculated with live fungus or sterile controls, and inspected each tree for the presence of fungal growth and woodpecker activity. Of 650 trees inoculated with fungus ( n  = 330) or a sterile control ( n  = 320), 528 (81.2%) were alive and standing in 2006 ( n  = 276 with fungus, 83.6%; n  = 252 control trees, 78.8%). Trees had been lost to harvest (11.1%), blowdown (3.8%), breakage (2.9%), and had died of undetermined causes (0.9%). A higher proportion of treatment trees displayed F. pinicola conks (0.200) and mycelia (0.073; inferred to be F. pinicola ) than did control trees (0.004 conks [unknown species], 0.012 mycelia), although the difference for mycelia was marginally significant. We also found that western hemlock ( Tsuga heterophylla ) had a higher proportion of conks (0.313) and evidence of any fungal growth (conks or mycelia; 0.393) than Douglas-firs ( Pseudotsuga menziesii ; 0.064 and 0.112, respectively). Further, we observed evidence of significantly ( P  = 0.010) more woodpecker excavations and sapsucker ( Sphyrapicus spp.) foraging holes associated with the fungal inoculations (6.2%) than at control trees (1.2%). Although use by woodpeckers was limited, we suggest that this finding is ecologically significant as we observed no woodpecker use, except for limited sapsucker foraging, when we inspected trees in 2002. The fungal inoculations completed 1997–1998, to some extent, were successful as F. pinicola was documented in at least 36.8% of the treated trees. In addition to F. pinicola , an ensemble of fungi and other microorganisms was established into the inoculation wounds of both control and treatment trees, suggesting that wounding of a healthy tree under the right circumstances may be sufficient to initiate this natural process in younger-aged forests as it occurs in old-growth forests.