Hardwood Stem Decays
Caused by several fungi
Host(s) in Alaska: All hardwoods
Habitat(s): Most decay heartwood, some occupy sapwood & heartwood
General information about hardwood stem decays in Alaska
A number of fungi cause heart rot in paper birch, trembling aspen, balsam poplar, cottonwood, and other hardwood species in Alaska. Phellinus igniarius is extremely widespread and common on both live and dead paper birch. Both Fomes fomentarius and Fomitopsis betulina are also widespread and common on paper birch but are found on dead trees and dead parts of live trees. Inonotus obliquus, found in very cold regions on live paper birch, is widely distributed throughout Southcentral and Interior Alaska. Considered a canker-rot, it is not often found on dead trees because it disintegrates soon after its host tree dies. There has been a marked increase in birch trees damaged by Chaga (Inonotus obliquus) collectors in recent years. Phellinus tremulae accounts for the majority of stem decay in trembling aspen.
Armillaria and Pholiota species are also common on hardwoods. They are generally considered root diseases, though they may contribute to decay in the butt and lower stem. Diplodia gall (Diplodia tumefaciens) causes damage superficially similar to Inonotus obliquus, but Diplodia gall occurs on aspen and affects tree growth hormones resulting in gall production rather than actively decaying stem tissue.
Select stem decay fungi of Alaskan hardwoods
Recent observations, key identification characteristics, and damage information is provided for each species. Click images to view albums of stem decay fungi from the Forest Health Protection, Forest Service, USDA, Alaska Region on Flickr. Detection maps show georeferenced observations of fungi, and many include the modeled range of tree hosts. Host tree distributions were developed by the Forest Health Assessment and Applied Sciences Team in 2011 (240m-resolution, presence based on dominant tree species by tree diameter). View our ground survey data dashboard to view maps and ground survey records of stem decays and other damage agents in Alaska.
Ganoderma applanatum (Pers.) Pat.
2024 Status/Activity: This common white rot of dead and down hardwoods and conifers across Alaska is considered a species complex that cannot be further distinguished in the field. On hardwoods in Southeast Alaska, the conk tends to be thinner and has a paler upper surface without the abundant dusting of brown spores.
2024 Ground Detection Survey Observations: 21 statewide, 17 across Southeast Alaska mostly on western hemlock, and 4 near Anchorage on balsam poplar and black cottonwood.
2024 iNaturalist Observations: 27 total, 15 in Southeast Alaska from Skagway to Ketchikan, 6 in the Interior, and 6 near Anchorage.
Hosts: Mainly hardwoods; but sometimes western and mountain hemlock, and white and Sitka spruce. General Distribution in Alaska: Statewide where hosts occur. Identification: Perennial, woody, fan- or shelf-shaped conk. Usually occurs as a saprobe on decaying logs and stumps. Occasionally found as a heart rot on wounds of living trees. Top: dull, dusty brown to grey-brown with concentric ridges. Bottom: white pore surface that immediately browns when touched. Interior: dark brown to cinnamon. Damage: Spongy mottled white rot of sapwood and heartwood. Remarks: Known as the artist’s conk because the fresh pore surface bruises dark brown when touched or scratched. Intricate etchings can be preserved for years if properly dried.
|
Image
Ganoderma applantum on dead trembling aspen near Moose Pass, AK. (USDA Forest Service photo by Alex Wenninger) |
Image
|
Click the image to view full Ganoderma applanatum album on Flickr.
Fomitopsis betulina (Bull.) B.K. Cui, M.L. Han & Y.C. Dai (=Piptoporus betulinum)
2024 Status/Activity: Birch conks are normal decay organisms of dead and dying birch and are often found fruiting alongside conks of Fomes fomentarius.
2024 Ground Detection Survey Observations: 8 observations, from Fairbanks south to the Anchorage area.
2024 iNaturalist Observations: 52 research grade observations, 30 from Southcentral, 17 from Interior, and 5 from northern Southeast.
Hosts: Birch.
General Distribution in Alaska: Southcentral and Interior Alaska; northern Southeast Alaska near Haines and Skagway.
Identification: Annual, leathery, shelving, light and corky conk. An extremely common saprobe of dead trees, also occurring on dead portions of live trees. Top: whitish to tan to mousy-brown, smooth or somewhat scaly. Lower margin of the cap incurving and projecting below the pore surface. Bottom: white pore layer when fresh, becoming yellowish to tan and slightly tooth-like when older. Interior: thick, white, firm, spongy when fresh and separates easily from the pore layer. Becomes corky with age.
Damage: Yellowish brown cubical rot of sapwood and heartwood. Advanced decay is very light weight and crumbles easily.
Remarks: Used as a bandage to prevent bleeding and infection in traditional medicine and has anti-inflammatory properties. Also called the Razor Strop fungus as barbers used the flesh to sharpen their razors.
|
Image
Fomitopsis betulina on birch in Anchorage Alaska. (USDA Forest Service photo by Alex Wenninger) |
Image
|
Click the image to view full Fomitopsis betulina album on Flickr.
Inonotus obliquus (Fr.) Pilát
2024 Status/Activity: No notable activity.
2024 Ground Detection Survey Observations: 5 observations along the road corridor from Denali State Park to Hope.
2024 iNaturalist Observations: 13 observations scattered from Yukon-Charley Rivers National Preserve to Katmai National Park and Preserve, but clusters of observations near Fairbanks and Anchorage.
Inonotus obliquus, also known as Chaga, is widespread throughout Interior and Southcentral Alaska and has been mapped on birch from the Kenai Peninsula north to the Brooks Range, and east to the Canadian border. As a true stem decay, this fungus does not require a wound as an infection court, nor does it invade dead trees. Diplodia gall appears superficially similar but occurs on aspen rather than birch.
Hosts: Birch.
General Distribution in Alaska: Southcentral and Interior Alaska.
Identification: Annual, leathery, shelving, light and corky conk. An extremely common saprobe of dead trees, also occurring on dead portions of live trees. Top: whitish to tan to mousy-brown, smooth or somewhat scaly. Lower margin of the cap incurving and projecting below the pore surface. Bottom: white pore layer when fresh, becoming yellowish to tan and slightly tooth-like when older. Interior: thick, white, firm, spongy when fresh and separates easily from the pore layer. Becomes corky with age.
Damage: Yellowish brown cubical rot of sapwood and heartwood. Advanced decay is very light weight and crumbles easily.
Remarks: Used as a bandage to prevent bleeding and infection in traditional medicine and has anti-inflammatory properties. Also called the Razor Strop fungus as barbers used the flesh to sharpen their razors.
|
Image
Chaga (Inonotus obliquus) on birch. (USDA Forest Service photos) |
Image
|
Click the image to view full Inonotus obliquus album on Flickr.
Phellinus tremulae (Bondartsev) Bondartsev & P.N. Borisov
2024 Status/Activity: No notable activity.
2024 Ground Detection Survey Observations: 1 observation near Nenana.
2024 iNaturalist Observations: 1 observation near Fairbanks.
This fungus is common throughout the range of aspen in Alaska and is considered the most important decay pathogen of aspen species in the Northern Hemisphere. Phellinus tremulae appears identical to other Phellinus spp. on birch but only occurs on aspen and rarely balsam poplar.
Hosts: Trembling aspen (P. tremulae) and possibly balsam poplar.
General Distribution in Alaska: Southcentral and Interior Alaska.
Identification: Perennial, woody, vaguely hoof-shaped conk. Occurs on live trees but can persist as a saprobe years after trees die. Top: dark brown to greyish-black to black, many small cracks. Bottom: convex, light brown with tiny circular pores. Interior: rusty-brown with numerous white flecks.
Damage: Initial decay is yellowish to yellowish-white, surrounded by a distinct dark zone line. Advanced decay is spongy or punky with numerous irregular, black zone lines. The presence of conks indicates considerable heart rot.
Remarks: Used to make punk ash. Phellinus igniarius is very common on live birch and looks identical to P. tremulae on aspen. Phellinus tremulae is the most important heart rot organism of aspen; in its commercial range in the Lower 48, it is reported to cause more volume loss than any other disease of aspen.
|
Image
Phellinus tremulae conk on aspen. (USDA Forest Service photo.) |
Image
|
Click the image to view full false tinder conk album (Phellinus tremulae and P. igniarius) on Flickr.
Phellinus igniarius (L.) Quél.
2024 Status/Activity: The incidence of this common, perennial fungus does not change much from year to year. The presence of conks indicates significant internal decay.
2024 Ground Detection Survey Observations: 14 total, 8 between Fairbanks and Healy in Interior Alaska, 1 in Denali State Park and 4 near Anchorage in Southcentral Alaska, and 1 near Haines in Southeast Alaska.
2024 iNaturalist Observations: 79 total, 34 in Interior Alaska near Fairbanks and 1 near Coal Creek on the Yukon River, 33 in Southcentral Alaska from Denali State Park to the Kenai Peninsula, and 11 in Southeast Alaska near Skagway.
Forest Health Protection is continuing a project with Research Plant Pathologist Dr. Mee-Sook Kim (USDA Forest Service Pacific Northwest Research Station) to explore the diversity of Phellinus species that occur on birch, willow, and alder in Alaska through molecular identification. Phellinus igniarius sensu lato (how we will refer to this species complex until we have more complete information) is widespread and common in Alaska on both live and dead birch trees, alder, and willow species.
Conks sampled from red alder in Southeast Alaska in recent years have been preliminarily identified as Phellinus lundellii based on PCR sequencing of the ITS region. Species identification will require sequencing multiple regions of DNA.
Hosts: Birch (P. igniarius).
General Distribution in Alaska: Statewide where hosts occur.
Identification: Perennial, woody, vaguely hoof-shaped conk. Occurs on live trees but can persist as a saprobe years after trees die. Top: dark brown to greyish-black to black, many small cracks. Bottom: convex, light brown with tiny circular pores. Interior: rusty-brown with numerous white flecks.
Damage: Initial decay is yellowish to yellowish-white, surrounded by a distinct dark zone line. Advanced decay is spongy or punky with numerous irregular, black zone lines. The presence of conks indicates considerable heart rot.
Remarks: Used to make punk ash. P. igniarius is very common on live birch and looks identical to P. tremulae on aspen. Phellinus tremulae is the most important heart rot organism of aspen; in its commercial range in the Lower 48, it is reported to cause more volume loss than any other disease of aspen.
|
Image
Phellinus igniarius on birch. (USDA Forest Service photo by Dr. Lori Winton.) |
Image
|
Click the image to view full false tinder conk album (Phellinus tremulae and P. igniarius) on Flickr.
2024 Status/Activity: The incidence of this common, perennial fungus on birch does not change much from year to year. The presence of conks indicates significant internal decay.
2024 Ground Detection Survey Observations: 14 total, 8 between Fairbanks and Healy in Interior Alaska, 1 in Denali State Park and 4 near Anchorage in Southcentral Alaska, and 1 near Haines in Southeast Alaska.
2024 iNaturalist Observations: 79 total, 34 in Interior Alaska near Fairbanks and 1 near Coal Creek on the Yukon River, 33 in Southcentral Alaska from Denali State Park to the Kenai Peninsula, and 11 in Southeast Alaska near Skagway.
Hosts: Birch; occasionally alder, aspen, balsam poplar, and cottonwood.
General Distribution in Alaska: Southcentral, Interior, and northern Southeast Alaska.
Identification: Perennial, woody, matte, and usually distinctly hoof-shaped conk. Extremely common saprobe of dead trees and dead parts of live trees. Top: zones of light grey to brown, dark grey, or black; smooth. Bottom: concave, tan to brown with small regular pores. Interior: thin brown layer between thick surface crust and several distinct layers of tubes; the dark brown tubes partially filled with white mycelium.
Damage: Early decay light brown. The presence of fruiting bodies indicates extensive advanced decay. Advanced decay soft, spongy, yellowish white rot, with blackish zone lines.
Remarks: Traditionally used to make fire tinder. Found on the 5000-year-old Oetzi Iceman in a pouch with flint. Also used to make felt-like Amadou. Sometimes confused with Phellinus igniarius
|
Image
|
Image
A Fomes fomentarius conk. (USDA Forest Service photo by Robin Mulvey.) |
Click the image to view full Fomes fomentarius album on Flickr.
Hebertson, L. 2005. Management Guide for Aspen Heart Rot. USDA-FS Regions 1 and 4. 6pp. Available here.
Worral, J. and M. L. Fairweather. 2005. Decay and Discoloration of Aspen. USDS-FS Forest Insect and Disease Leaflet FS-R6-RO-FIDL#149. 7pp. Available here.
Pocket guide for the identification of common forest diseases and insects in Alaska.
Content prepared by Robin Mulvey, Forest Pathologist, Forest Health Protection, robin.mulvey@usda.gov