Decayed Wood Advisor


Stem Decays

Key Wildlife Value:

Stem decay fungi are essential to the development of wildlife habitat in dead wood. They soften wood, causing it to become an attractive and useful substrate for excavation by cavity nesters and carpenter ants. Some decay fungi also cause the formation of hollow trees. Hollows cannot form once a tree has died; they form only in living trees infected with heartwood decay fungi. A hollow tree is formed when certain heartwood decay fungi cause advanced decay that collapses, leaving a protective shell of live sapwood surrounding a hollow chamber. Decayed stems frequently become weakened and break, creating broken tops, down wood, and unique bole structures useful to wildlife for nesting, roosting, and resting. Stem breakage caused by decay fungi also contributes to canopy gap formation with associated increases in forest structural diversity and sometimes, compositional diversity. Decay-softened wood provides favorable habitat for other decomposer organisms that form the basis of the food chain in forest ecosystems. Fruiting bodies and other parts of some decay fungi are fed upon by wildlife. Decay fungi also play a significant role in recycling wood to soil.

Distribution in Oregon and Washington:

Found throughout both states.


All species of trees are hosts to one or more species of stem decay fungi. Table 1 provides a summary of important stem decay species found in Oregon and Washington and their respective hosts


Fungal fruiting bodies, which typically are leathery or woody conks or sometimes mushrooms, usually provide the most obvious and diagnostic indications of stem decay. However, fruiting bodies are not always present on decayed trees. Look for fruiting bodies on the tree bole (Note: Phaeolus schweinitzii most commonly fruits on the ground around the base of the tree rather than on the tree bole). Fruiting bodies may be annual or perennial. Old woody conks that fall to the ground beneath the tree sometimes prove useful for diagnosing stem decay in the absence of other visible conks.

Some decay species affect one specific wood component, such as heartwood or dead sapwood, while others affect both heartwood and dead sapwood. As a general rule, heartrot fungi tend to produce conks that are few in number and associated with dead and live branch junctions, compared to saprots and other saprophytic fungi, which tend to produce large numbers of conks that are randomly located over the tree bole surface. Other decay indicators include punk knots, broken boles, flat faces, bole scars, bayonet tops, forked tops, openings into the stem interior, and piles of sawdust at the base of the tree caused by carpenter ant activity. Trees that are hollow at the base sometimes may be detected by “sounding” the bole with an axe or sturdy stick.

Life History:

Heart rot fungi survive primarily in the heartwood of living trees, and spread via airborne spores produced by fruiting bodies. The spores cannot penetrate living sapwood, but gain entry to trees by colonizing exposed dead wood at dead branch stubs, open knots, and bole wounds. Spores germinate and develop into vegetative structures capable of extracting nutrients from wood. The digestion of various wood components results in wood decay. Two types of decays are recognized; white rots and brown rots. White rots create decayed wood that often tends to be lighter in color, with a stringy texture or a pocketed appearance. Brown rots create columns or pockets of decayed wood that is dark brown, dry and fragile, and that tends to break up into cubes or to easily crumble. The decay process is usually slow, taking from many years to several decades for advanced decay to develop. Some heart rot fungi stop decaying after the tree dies, while others may continue developing in wood after a tree has fallen or even after the tree has been made into lumber, but all heartwood fungi require a living tree for initial establishment. Fruiting bodies vary in form from fleshy mushrooms to woody brackets called conks. They often are produced only after extensive decay has developed, and usually occur on the bole in association with living and dead branches, branch stubs, and knots.

Life histories of sap rot fungi are similar to those of heart rot fungi, except they primarily colonize dead sapwood.

Important Habitats and Spread Dynamics:

Heartrots are generally more prevalent in unmanaged stands, old growth stands, in older trees (which often are larger trees), and in stands where trees have suffered frequent or extensive wounding, such as previously partially cut stands with multiple entries, old burned areas, or areas where frequent breakage occurs due to snow, wind, or ice. Heartwood decay spread typically is a relatively slow, gradual process that involves a cycle of wounding (enabling infection or activation), decay, and breakage. When tree boles decayed by heartrot fungi break, they often strike and wound nearby trees as they fall. Windborne decay fungus spores may then infect these wounded trees, or, as in the case of Indian paint fungus (Echinodontium tinctorium), dormant infections may be activated. The wounded trees then develop decay and eventually break, perpetuating the cycle. The effect of this small-scale disturbance in most mature forests is a series of small, shifting canopy gaps. Occasionally, when infection levels are extremely high, an unusually severe storm event will interact to cause levels of breakage resulting in canopy gaps several acres in size.

Saprots and other saprophytic wood decaying fungi are most prevalent in dead standing and down trees. They may occur on dead portions of the bole of living trees, or rarely, on severely weakened trees just before they die. They are spread by windborne spores or sometimes are carried into trees by excavating insects. Mycelial fragments of commonly occurring Polyporous volvatus are carried from infected into uninfected trees by many species of bark beetles and wood borers. Saprots play an important role in providing substrates for cavity excavation in trees that have thick sapwoods, such as ponderosa pine.

Opportunities for Manipulation to Increase Wildlife Habitat:

Artificial inoculation of trees with heartwood decay fungi can be used to create internal decay in sound, living trees in areas where cavity-nesting habitat is deficient. With this technique, cultured wooden dowels, inoculated in the laboratory with locally selected strains of fungi, are inserted by tree climbers into pre-drilled holes in living tree boles. The entire process of fungal material collection, isolation, culture, and inoculation requires at least eight months.

Mature trees may be intentionally wounded by topping, limbing, or removing large sections of bark from the bole, in hopes of initiating colonization by stem decaying fungi or activating dormant infections of Indian paint fungus. This method has less certainty of producing desired results than artificial inoculation, however, due to inherent uncertainties regarding the colonization of the wounded area or the occurrence and location of dormant infections of Indian paint fungus.

Potential Adverse Effects:

Decay caused by a few species, especially Indian paint fungus, Phellinus pini, and Phaeolus schweinitzii, may sometimes be so prevalent in older, predominantly host species stands that undesired degradation of the existing stand structure occurs as a result of high-levels of stem breakage. High levels of stem decay can also cause significant losses in stand productivity due to decay and associated breakage. On recreational sites, trees with advanced decay have a high potential for failure and can present a significant public safety hazard.

How to Minimize the Risk of Adverse Effects:

Reduce injury to residual trees during selective harvest activities by limiting the number of entries, restricting the operating season to summer, fall, and winter when wounding is less likely to occur, limiting the size and type of equipment, and controlling falling and skidding practices. Use pruning techniques that promote fast healing of pruning wounds to avoid creating entry points for heartrot fungi. Pile slash away from the bases of residual trees after harvesting. Avoid underburning stands with a substantial component of true firs. Use short rotations. On recreational sites, trees having indicators of decay or discernable decay exceeding prescribed levels should be topped to a safe height or removed if they are within striking distance of a target.


Aho, P.E., G. Fiddler, and G.M. Filip. 1989. Decay losses associated with wounds in commercially thinned true fir stands in northern California. USDA Forest Service, Pacific Northwest Research Station, Portland, OR, Research Paper PNW-RP- 403. 8pp.

Aho, P.E., G. Fiddler, and M. Shigo. 1983. Logging damage in thinned, young-growth true fir stands in California and recommendations for prevention. USDA Forest Service, Pacific Northwest Research Station, Portland, OR, Research Paper PNW-304. 8pp.

Allen, E. A., D.J. Morrison, and G.W. Wallis. 1996. Common tree diseases of British Columbia. Canadian Forest Service, Victoria, B.C. 178 pp.

Bedker, P.J., J.G. O’Brien, and M.E. Meilke. 1995. How to prune trees. USDA Forest Service, Northeastern Area, State and Private Forestry, NA-FR-01-95. 30 pp.

Bull, E.L., C.G. Parks, and T.R. Torgersen. 1997. Trees and logs important to wildlife in the interior Columbia River Basin. USDA Forest Service, Pacific Northwest Research Station, Portland, OR. PNW-GTR-391. 55 pp.

Filip, G.M., and C.L. Schmitt. 1990. Rx for Abies: silvicultural options for diseased firs in Oregon and Washington. USDA Forest Service, Pacific Northwest Research Station, GTR-PNW-252. 34p.

Goheen, E.M., and E.A. Willhite. In prep. Field Guide to the Common Diseases and Insect Pests of Oregon and Washington conifers. USDA Forest Service, Pacific Northwest Region, Forest Health Protection.

Hansen, E.M. and K.L. Lewis, eds. 1997. Compendium of conifer diseases. American Phytopathological Society Press. 101 pp.

Hennon, P.E. 1995. Are heart rot fungi major factors of disturbances in gap-dynamic forests? Northwest Science, 69(4):284-293.

Hepting, G.H. 1971. Diseases of Forest and Shade Trees of the United States. USDA Forest Service, Ag. Handbook 386. 658 pp.

Maser, C. and Trappe, J.M. (technical editors). 1984. The seen and unseen world of the fallen tree. USDA Forest Service, Pacific Northwest Research Station, Portland, OR, PNW-GTR-164. 56 pp.

Parks, C. and D. Hildebrand. In prep. Experimental techniques for inoculation of trees with stem decay to create wildlife habitat -- laboratory and field procedures. USDA Forest Service, Pacific Northwest Research Station, Draft USDA Forest Service Handbook. 24pp.

Scharpf, R.F. 1993. Diseases of Pacific Coast Conifers. USDA Forest Service, Pacific Southwest Research Station, Albany, CA, Ag. Handbook 521. 199 pp.

Website links

Rot and decay links, An Online Catalog of Western Forest Insects and Diseases

The Seen and Unseen World of the Fallen Tree, USDA Forest Service General Technical Report

How to Prune Trees, USDA Forest Service publication

not yet available: Field Guide to the Common Diseases and Insect Pests of Oregon and Washington Conifers

Table 1. Summary of important stem decays of Oregon and Washington and their hosts.
Common Name
Scientific Name
Aspen trunk rot Phellinus tremulae Trembling aspen
Brown crumbly rot (red belt fungus) Fomitopsis pinicola Most western conifers
Brown cubical butt and pocket rot of cedar Oligoporus sericeomollis Western redcedar
Brown cubical rot (sulfur fungus) Laetiporus sulphureus Douglas-fir, true firs, pines, hemlocks spruces, larch, western redcedar, oaks, maples, ash, Prunus spp., willows, and various other hardwoods.
Brown stringy trunk rot of hardwoods Spongipellis delectans Cottonwoods, maples, alders, and oaks
Brown top rot (rose conk) Fomitopsis cajanderi Douglas-fir, grand fir, larch, lodgepole pine, ponderosa pine, white pines, hemlocks and spruces
Brown trunk rot (quinine fungus) Fomitopsis officinalis Douglas-fir, pines, western larch, spruces, and hemlocks; occasionally on true firs
Grey brown saprot (pouch fungus) Cryptoporus volvatus All conifers
Hardwood trunk rot (false tinder conk) Phellinus igniarius Maples, alders, paper birch, black cottonwood, and many other hardwoods
Mottled rot (yellow cap fungus) Pholiota adiposa, P. limonella True firs, hemlocks, pines, and spruces.
Mottled rot (yellow cap fungus) Pholiota populnea Black cottonwood
Pitted sap rot (purple conk) Trichaptum abietinum All conifers
Pocket dry rot (pecky rot) Oligoporus amarus Incense-cedar
Red ring rot (white speck) Phellinis pini Douglas-fir, western larch, pines, hemlocks, spruces, true firs, western redcedar and rarely incense-cedar
Red ring rot canker (butterfly conk) Phellinis cancriformans Grand fir, white fir, Shasta red fir, noble fir, Pacific silver fir, and subalpine fir
Redwood cubical rot Oligoporus sequoiae Coast redwood
Rust red stringy rot (Indian paint fungus) Echinodontium tinctorium True firs and hemlocks
Scaly cap fungus Neolentinus lepideus Pines, western redcedar, incense cedar, hemlocks, true firs, and Douglas-firs
Schweinitzii root and butt rot (velvet top fungus) Phaeolus schweinitzii Douglas-fir, western larch, Engelmann spruce, Sitka spruce, lodgepole pine, ponderosa pine, Jeffrey pine, western white pine, and sugar pine; occasionally true firs, hemlocks, and western redcedar
Sterile conk rot of birch (cinder conk) Inonotus obliquus Paper birch; rarely on cottonwood
Stringy butt rot (yellow root rot) Perenniporia subacida Hemlocks, Douglas-fir, lodgepole pine, western larch, grand fir, and western redcedar
Tinder Conk Fomes fomentarius Paper birch, alders, black cottonwood
White mottled rot Ganoderma applanatum Maples, alders, oaks, willows, and many other hardwoods and conifers
Yellow pitted rot (coral fungus) Hericium abietis True firs, hemlocks and spruces
Yellow ring rot in western redcedar Phellinus weirii Western redcedar