Tree Wounding and Decay Guidebook Table of Contents]


Forest tree decays are widespread throughout all forested ecosystems of British Columbia, occurring on both broadleaf and conifer hosts. Decay pathogens are an integral part of these forested ecosystems and can be viewed as both beneficial and detrimental to the health, function and productivity of forests.

Decay is the process of disintegration by which sound wood is decomposed. A pathogen is the actual agent of decomposition, usually a fungus or other micro-organism. Tree decay fungi reduce lumber recovery, lower lumber and chip quality and can cause dangerous conditions in recreation areas. Tree decay may lead to early tree mortality from a variety of factors, such as breakage, blowdown or predisposition to other forest health factors. Decay fungi also play an important role in creating gaps in forest canopies and play a lead role in nutrient cycling, species succession, biodiversity and the creation of wildlife habitat. The biology of decay fungi is such that harvesting, regeneration and stand management activities can affect the competitive behavior of decay pathogens in ecosystems.

An important principle of forest management is that the role of decay fungi in each ecosystem must be understood. Forest management objectives and prescriptions should then be set in light of the constraints of pathogen biology.

While there are a myriad of decay pathogens that may have implications for stand prescriptions, they can be separated into four broad categories:

Do not consider the standards set forth in this guidebook as definitive or absolute; nor should they be used to form the basis for any punitive action. This guidebook offers very general recommendations for dealing with tree decays in the prescription. The intent is to provide the user with several concepts and estimates of the probable outcome of prescribed activities. Hopefully, these recommendations will give the user a reasonable understanding of the action and effect of decays, to help achieve the desired objectives of the prescription.

This guidebook provides:

Major decay groups in B.C. forests

The four major wood decay groups are differentiated by the type of wood decay they cause and the type of tree they infect. The differences between these groups are based on the wood components they use.

Conifers are affected by brown, white and white pocket rots. Wood decayed by white rots is light-colored and spongy. The fungi that cause white rots simultaneously break down the three major components of wood: lignin, cellulose and hemicellulose.

Brown rot decay is typically brown and crumbly. These fungi primarily decay the cellulose and hemicellulose components, leaving the lignin. Wood decayed by brown rot has very little strength, due to the loss of cellulose.

White pocket rot fungi, as the name implies, cause white pockets or pits to develop in the decaying wood. White pocket rot fungi selectively break down lignin and hemicellulose and degrade cellulose to a much lesser extent. In the white pockets, lignin is selectively degraded while much of the cellulose remains.

The fourth group of stem decays are those that affect broadleaf trees. All of the broadleaf decay fungi covered in this guide are white rots.

There are other methods of grouping wood decay fungi. One method used by Etheridge (1973) is to group wound parasites according to substrate preference and mode of attack. Primary invaders such as Stereum sanguinolentum and Heterobasidion annosum attack fresh, previously uncolonized wound surfaces to gain entry into the heartwood. These primary invaders cause extensive heart rot in living trees and are usually displaced by other organisms when the tree dies.

Secondary invaders such as Ganoderma applanatum favor wound substrates previously colonized by other micro-organisms. Many of these secondary invaders continue to develop in host trees after they have died and play a role in decomposing woody material.

A third group is composed of fungi such as Fomitopsis pinicola that apparently have no special substrate requirements. These species may attack either uncolonized or previously colonized wound surfaces on living trees or act as true saprophytes on dead material. With few exceptions, all wound parasites complete their life cycle on dead material.

Major wood decay fungi in B.C.

There are far too many decay organisms in the forests to detail each individually in this guide. Only the key decay organisms that may affect prescriptions and practices are listed in the table below.

Table 1. Common decay fungi and their hosts

Scientific name Common name Host(s)

Phaeolus schweinitzii Velvet top fungus All conifers
Fomitopsis pinicola Red belt fungus Conifers and broadleafs
Fomitopsis officinalis Quinine conk Conifers
Phellinus weirii (cedar form) Cedar butt (yellow ring) rot Cwa
Postia sericeomollis Cw
Stereum sanguinolentum Red heart rot or Bleeding fungus Conifers except Cw
Echinodontium tinctorium Indian paint fungus Conifers (rarely Fd or Sx)
Pholiota spp. Yellow cap fungus B, Hw, P, Sx
Heterobasidion annosum Annosus root rot Conifers and broadleafs
Armillaria sinapina Saprophytic Armillaria Conifers and broadleafs
Phellinus pini Pini (red ring) rot or white pocket rot All conifers
Ganoderma applanatum Artist's conk Conifers and broadleafs
Phellinus igniarius False tinder conk Ep, (other broadleafs)
Phellinus tremulae Aspen trunk rot At, (Ac)
Fomes fomentarius Tinder conk Ep, (other broadleafs)

a Refers to genus and species symbols for trees found in Minimum Standards for the Establishment and Remeasurement of Permanent Sample Plots in British Columbia, Forest Productivity Councils of British Columbia, revised September, 1995.

While this list may appear formidable at first, general trends can be seen among most of these fungi. This guide will help you to effectively prescribe for and manage these decays in forest operations.

Signs and symptoms of some common wood decay fungi

Many decay-causing fungi have distinctive fruiting bodies that are useful for identification. Without these fruiting bodies, it is often difficult to tell decays apart, beyond the broad decay group classifications mentioned previously. The majority of decay-causing fungi are not specific to host species, although some exceptions may be useful for identification. The major decay-causing fungi and the factors used for identifying them are outlined in Table 2.

Table 2. Summary of factors used to identify common decay fungi in B.C.

Conk color
a) top, b) bottom
Fruiting body
Wood decay
Means of entry

a) red-orange to brown
b) brown
shelf or cluster
on ground
red-brown cubical butt
rot, irridescent sheen
roots, basal trunk
wounds, fire scars

a) grey to dark brown,
    red margin
b) white
thick shelf-like,
light brown stain,
brown cubical rot with
white mycelial felts
insect and fire-
caused wounds

a) white or dark
b) white
hoof or cylindric with
chalky surface
brown cubical with
thick mycelial felts
wounds, fire scars

Phellinus weirii
(cedar form)
a) brown-grey
b) cream
shelf-like conk,
laminated white heart
root contacts

creamy white thin crust-like form
on end of logs or
on slash
yellow-brown stain,
brown cubical butt
rot in pockets
basal trunk

a) brown-grey
b) brown, blood-red
    if bruised
small thin bracket
shelf, common on
slash and log ends
red-brown heartwood
stain, brown stringy rot
trunk wounds,
freshly exposed

a) dark grey
b) light grey, spiny
thick hoof-shaped
bracket, rough
concentric rings
light brown water-
soaked stain, brown
stringy rot
small branch stubs
(spores dormant
until tree injured)

Pholiota spp. scaly, sticky
gilled mushroom,
occurs in clusters
dark brown streaks
forming holes or
pockets in heartwood
basal wounds, fire
scars, frost cracks

creamy porous
lower surface
perennial crust-like
found on upturned
tree butt and roots
yellow- to red-brown
stain, white spongy
rot with black flecks
fresh basal trunk
wounds, infected
root contact

mushroom, black
rhizomorphs and
white mycelial fans
under bark
light brown water
soaked stain, light
yellow-white spongy
to stringy butt rot,
black zone lines
root contacts with
infected trees

Phellinus pini a) dark grey
b) brown, angled pores
shelf-like, perennial,
velvety margin
red stain, often in
rings, white pocket rot
branch stubs

a) grey or tan
b) white, brown when
large, shelf-
like perennial,
concentric rings
bleached and ringed
by dark brown stain,
white spongy rot
mostly on old
trees but can enter
trunk wounds

a) black or grey, rough
    deeply zoned
b) brown
hoof-shaped, perennial,
concentric rings on
upper surface
yellow-white heartwood
stain surrounded by
green-brown zone,
soft yellow-white rot
with black zone lines
knots, branch stubs
and wounds

a) black or grey,
    rough, zoned
b) brown
hoof-shaped, perennial,
concentric rings
on upper surface
(see P. igniarius) knots, branch stubs
and wounds

a) white or grey
b) brown
hoof-shaped, perennial,
concentric rings on
upper surface
slight brown
discoloration yellow-
white spongy rot,
brown-black zone lines