Fungi evaluated for increasing habitat diversity in managed conifer forests

Standing trees with internal decay or “heart rot” are an important habitat component for some birds and wildlife in Washington. Rotted wood is soft and easier to excavate into nest cavities. Nests high in standing trees provide additional protection from some ground predators. Living trees with decay and cavities persist longer as effective nesting sites than dead trees or snags do.

A climber installing a dowel into a large tree in Western Washington in 2001. Photo: Dan Omdal/DNR.

In many places, large trees with internal decay have been depleted by logging practices that reduce the number of large, old trees and remove dead trees. Washington’s Forest Protection rules require leaving some large trees and snags as habitat when harvesting timber, but it takes decades of time for natural wounds and internal decay to develop. Recently, DNR and US Forest Service forest pathologists have been working with wildlife biologists and foresters to evaluate ways of inoculating living trees with wood rotting fungi in an attempt to quickly and reliably produce long-lasting, effective internal decay in living trees.

tree cross section
A tree’s cross section, cut just above the inoculation site. The staining and softened texture indicate the initiation of decay. Photo: Dan Omdal/DNR.

The group initially collected heart-rot fungi from forested sites around Washington and Oregon and grew it on hemlock dowels. Then tree climbers drilled holes high in the trunks of selected trees, inserted one fungus-infected-dowel per hole and capped it with a short piece of plastic pipe to prevent the hole from closing over. In 2010, they returned to some of these trees (now 7- to 14-years since the inoculation) to cut down some of the treated trees in order to observe whether any decay was occurring, measure the extent of any decay, and see whether wildlife had started using the sites. The results of this project are published online at: “Seven- to 14-Year Effects of Artificially Inoculating Living Conifers to Promote Stem Decay and Subsequent Wildlife Use in Oregon and Washington Forests.”

Split section of infected tree
Split section of a tree containing a fungus-infected dowel and pvc pipe plug. The dark colored wood interior to the inoculation is decayed. Photo: Dan Omdal/DNR.

Although no wildlife was yet observed using the inoculation sites, these treatments did result in successful colonization by heart rot fungi and development of internal decay. Some important observations include:

  • The recommendation to drill three holes at each inoculation site in order to create a larger volume of decayed wood more quickly;
  • Fomitopsis cajanderi “brown top rot” appeared to cause the most decay in westside Douglas-fir;
  • Fomitopsis officinalis “quinine fungus” was most effective for inoculating several eastern Washington tree species; and
  • Fast growing trees may not be good candidates for this treatment because they produce such thick layers of hard, sound wood outside the internally decayed area that it would likely be difficult for a bird or animal to excavate and reach the decayed area.

Additional inoculated trees remain standing and will be evaluated in future years.

 By Karen Ripley, Forest Health Program Manager
Washington State Department of Natural Resources