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.
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.
Table 1. Summary of important stem decays of Oregon and Washington and their hosts.
|Common Name||Scientific Name||Hosts|
|Aspen trunk rot||Phellinus tremulae||Quaking aspen|
|Brown crumbly rot (red belt fungus)||Fomitopsis pinicola||Most western conifers|
|Brown cubical butt and pocket rot of cedar||Postia sericeomollis||Western redcedar|
|Brown cubical rot (sulfur fungus)||Laetiporus conifericola, L. gilbertsonii||L. conifericola - Douglas-fir, true firs, pines, hemlocks, spruces, larch, western redcedar L. gilbertsonii – oaks and eucalyptus|
|Brown stringy trunk rot of hardwoods||Spongipellis delectans||Black cottonwood, 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)||Laricifomes officinalis||Douglas-fir, pines, western larch, spruces, and hemlocks; occasionally on true firs|
|Hardwood trunk rot (false tinder conk)||Phellinus igniarius||Maples, alders, quaking aspen, paper birch, black cottonwood, oaks, golden chinquapin, and many other hardwoods|
|Heterobasidion root disease (root and butt decay)||Heterobasidion occidentale, H. irregulare||H.occidentale – true firs, hemlocks, Douglas-fir, spruces H. irregulare – pines, junipers, incense cedar, oaks and various other hardwoods|
|Innonotus trunk rot||Inonotus dryophilus, I. dryadeus, I. andersonii||Primarily oaks, occasionally other hardwoods and conifers|
|Juniper pocket rot||Pyrofomes demidoffii||Western juniper|
|Mottled rot (yellow cap fungus)||Pholiota adiposa, P. limonella, populnea||True firs, hemlocks, pines, spruces, yew, alders, quaking aspen, black cottonwood, maples; infrequently on willow|
|Pitted sap rot (purple conk)||Trichaptum abietinum||All conifers|
|Pocket dry rot (pecky rot)||Oligoporus amarus||Incense-cedar|
|Red heart rot||Stereum sanguinolentum||Spruces, Douglas-fir, hemlocks, true firs, pines, western larch, and true firs|
|Red ring rot (white speck)||Porodaedalea pini||Douglas-fir, western larch, pines, hemlocks, spruces, true firs, yew; infrequently on western redcedar, western juniper, oaks, maples, rarely on incense-cedar, Alaska yellow cedar, Port-Orford-cedar, and alders|
|Red ring rot canker (butterfly conk)||Porodaedalea cancriformans||Grand fir, white fir, Shasta red fir, noble fir, Pacific silver fir, and subalpine fir|
|Redcedar white ring rot||Ceriporiopsis rivulosa||Western redcedar|
|Redwood cubical rot||Oligoporus sequoiae||Coast redwood|
|Rust red stringy rot (Indian paint fungus)||Echinodontium tinctorium||True firs and hemlocks; infrequent on Engelmann spruce|
|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 black cottonwood|
|Stringy butt rot (yellow root rot)||Perenniporia subacida||Hemlocks, Douglas-fir, lodgepole pine, western larch, grand fir, and western redcedar|
|White mottled rot||Ganoderma applanatum||Maples, bay laurel, alders, oaks, willows, and many other hardwoods and conifers|
|White pocket rot (lion’s mane fungus)||Hericium erinaceus||Oaks, maples, ash, and a wide variety of other hardwoods|
|White spongy trunk rot (tinder conk)||Fomes fomentarius||Paper birch, alders, black cottonwood, willows, oaks, quaking aspen, cherries, and maple|
|White trunk rot of conifers||Phellinus hartigii||Hemlocks, true firs, and yew|
|White trunk rot of hardwoods||Phellinus robustus, P. everhartii, P. gilvus||Oaks|
|Yellow pitted rot (coral fungus)||Hericium abietis||True firs, hemlocks and spruces|
|Yellow ring rot in western redcedar||Coniferiporia weirii||Western redcedar|
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 sapwood, while others affect both heartwood and sapwood. As a general rule, heartrot fungi tend to produce conks that are few in number and associated with living and dead branch junctions, branch stubs, and knots, 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.
Heart rot fungi survive primarily in the heartwood of living trees, and spread via airborne spores produced by fruiting bodies. Spores germinate and develop into vegetative structures capable of extracting nutrients from wood. The spores typically gain entry to trees by colonizing exposed wood at bole breaks, bark wounds, or branch stubs, and some enter through root stubs or damaged roots. Infections in young trees can initiate a sequence of processes that result in long-term internal decay and cavities in large, mature trees. In general, a tree resists the spread of invading fungi and bacteria through a process called compartmentalization, which can confine invaders to the wood present at the time of wounding. As the tree continues to grow each year, it forms successive outer layers of sound, healthy wood that cover the colonized wood, and over time the colonized sapwood is converted into heartwood. To various degrees, heartrot fungi are able to overcome compartmentalization barriers and their 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. Fruiting bodies vary in form from fleshy mushrooms to woody brackets called conks. They often are produced only after extensive decay has developed.
Life histories of sap rot fungi are similar to those of heart rot fungi, except their activity is primarily restricted to sapwood.
Some stem decay fungi, such as Fomitopsis pinicola, cause decay in both sapwood and heartwood.
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 Cryptoporus volvatus are carried from infected into uninfected trees by many species of bark beetles and wood borers. Saprots and other saprophytic wood decaying fungi, especially the very widespread and commonly occurring Fomitopsis pinicola and Trichaptum abietinum, play an important role in providing suitable substrates for cavity excavation in trees that have thick sapwoods, such as ponderosa pine.
Intentional wounding of mature trees that mimics the placement and size of natural wounds may initiate colonization of stem decaying fungi or activate dormant infections. Mature trees in decay-deficient second-growth stands 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. Because tree injuries from commercial logging activities and prescribed burning mimic natural wounds from natural tree failure, weather, and wildfire, allowing or encouraging residual tree wounding during commercial logging activities may eventually result in decay that provides habitat for cavity-dependent wildlife and contributes over the long term to canopy gaps through tree breakage. Tree wounding may be encouraged during selective harvest activities by operating during spring when wounding is more likely to occur, and relaxing some controls over falling and yarding practices. Unintentional logging wounds occur most frequently in the lower boles and crowns, however, many cavity-dependent species prefer the habitat zone of the upper tree crown. Intentional wounding and top-breakage with logging equipment that targets the upper crowns of selected residual trees can encourage the development of upper bole stem decay columns in live trees. Underburning stands having a component of true firs or hemlock is likely to result in wounding with subsequent decay that is located in the basal portions of tree boles. It should be noted that methods of intentional wounding have inherent uncertainties regarding the colonization of the wounded area by stem decay fungi or the occurrence and location of dormant infections.
Artificial inoculation with heartwood decay fungi to create cavity-nesting habitat in sound, living conifers is a potential strategy that requires further development in Oregon and Washington before operational application can be recommended. Evaluations of trial results by Filip et al. (2004) and Filip et al. (2011) indicate that the tested artificial inoculation methodologies were slower, costlier, and less to no more effective in producing stem decay within a 5-10 year period than other lower-input methods, such as tree topping or shooting sterile dowels into trees using a shotgun or rifle. Further testing and refinement of substantially modified artificial inoculation methodology is needed before artificial inoculation can be considered a viable operational strategy in Oregon and Washington.
Decay caused by a few species, especially Echinodontium tinctorium (Indian paint fungus), Porodaedalea pini (Red ring rot), and Phaeolus schweinitzii (Schweinitzii root and butt rot), 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 and administrative sites, trees with advanced decay often have a high potential for failure and can present a significant safety hazard.
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 or hemlock. Use short rotations. On recreational and administrative sites, trees within striking distance of a target and that have indicators of decay or discernable decay exceeding prescribed levels should be removed or topped to a safe height, or the situation arranged so that people are not exposed to danger.
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