CG PARKS¹, EL BULL¹ and GM FILIP²

¹USDA Forest Service, Pacific Northwest Research Station, La Grande, OR 97850, USA; ²Oregon State University, Forest Science Department, Corvallis, OR 97331, USA

Background and objectives
Many species of forest wildlife depend on tree cavities for nesting or resting sites. Most cavities found in coniferous forests have been excavated by woodpeckers who make new cavities for nesting every year and excavate in dead or living trees softened by decay fungi. Woodpecker cavities, once abandoned by their makers, are used by many species of birds, mammals, and herptiles, who are cavity-dependent but unable to excavate for themselves. Managing for cavity-dependent wildlife is a major issue for forest managers in the United States. Managers of public forests are required to retain some decaying trees for habitat during timber harvests, but in some forests all appropriate trees have already been removed. There is great interest in developing ways to create suitably decayed trees for cavity-nesting habitat where it is needed. The objectives of our study in progress are to identify which fungi are naturally associated with woodpecker cavities in living trees and to develop an artificial inoculation method that can be used as a tool to selectively decay trees for wildlife habitat management.

Materials and methods
We sampled living conifers with woodpecker nest cavities by collecting wood cores adjacent to the nests [1, 2]. Sectioned cores were cultured on malt extract agar and the decay fungi (Basidiomycetes) associated were identified. Inoculum was developed by growing pure fungal cultures on wooden dowels. Dowels were inserted in trees 6 to 12 m above ground level. Trees are monitored annually for evidence of woodpecker excavations.

Results and conclusions
Preliminary results find that after 6 years all of the inoculated trees (n=60) contained decayed wood and 14% of trees are being used by woodpeckers and secondary cavity nesters. All inoculated trees remain alive with viable crowns. Because of the biology and natural abundance of airborne spores of the decay fungi used, there is no likelihood of spread into non-target trees. These preliminary results suggest that inoculation may be a viable tool to create suitable habitat for cavity-dependent wildlife in coniferous forests in greater abundance or at younger ages than would naturally occur.

Additional field trials are being conducted across the western United States to test inoculation in a range of different forest conditions and inoculation delivery methods, for example, ballistics. All trials use locally occurring decay fungi.

References
1. Parks CG, Bull EL, Filip GM, Gilbertson RL. 1996. Plant Disease 80, 959.
2. Parks CG, Raley CM, Aubry KB, Gilbertson RL. 1997. Plant Disease 81, 551.