Decay fungi can be categorized according to the type of rot produced: soft, white or brown.

Soft rots are caused by Ascomycetes and are facilitated by enzymes that adhere to the hyphal cell wall, therefore decay does not occur in advance of the fungus.

White rots are caused by Basidiomycetes. These fungi are able to breakdown cellulose and lignin. The cellulases produced are primarily exocellulases, and operate in advance of the fungus.

Brown rots are caused by Basidiomycetes. These fungi can only break down cellulose, but the cellulase enzymes produced are both exo- and endocellulases. Decay and strength loss occurs quickly and operates in advance of the fungus.

Decay fungi can also be categorized according to the means of entering the host, and where the fungus operates. Three general categories are recognized: true heartrots, wound-entry heartrots, and sapwood rots.

True Heartrots:

These fungi exist in the heartwood, do not require a wound to enter the tree, and consistently produce fruiting bodies on living trees.
Echinodontium tinctorium Indian Paint Fungus

Host: true firs, hemlocks, occasionally on D-fir, cedar, and spruce.
Damage: cause a stringy yellow rot. Infection thought to occur through small branchlets, then is radially overgrown until it can access the heartwood. This can take 40 years or more.
Conks: have teeth, not pores on the fertile layer, have a bright orange context, and are dark black/brown with a rough outer surface. Typically grow from branch stubs.

Phellinus pini Red Ring Rot

Host: widely distributed, wide host range, most frequent on hemlock, spruces, larch, Douglas-fir and cedar.
Damage: causes a white pocket rot, is a major cull agent because of its wide distribution. Unknown mode of entry.
Conk: has a yellowish fertile layer, large pores, rough, ridged surface.

Phellinus ignarius, Phellinus tremulae False Tinder Fungus

Host: ignarius is found on birch, tremulae on aspen
Damage: may cause more loss than any other decay fungus on hardwoods.
Conk: is black with a rough surface and brown fertile layer.

Wound Entry Heartrots:

These fungi invade the heartwood through a wound, such as scars, frost cracks, broken tops, cankers, etc.
Fomes officinalis Quinine Conk

Host: wide range of conifers, especially Larch, spruce and Douglas-fir
Damage: brown cubical heartrot, continuing decay of dead trees.
This fungus has been known since antiquity as the source of agaricin, a medicine used to treat diseases such as tuberculosis. Also produces quinine, used to treat malaria.

Fomes fomentarius White Spongy trunk Rot

Host: primarily Birch however also reported on alder, balsam poplar and cottonwood in British Columbia.
Damage: causes a white rot in both sapwood and heartwood. Decay is caused in both living and dead trees.
Conks: are perennial, woody or leathery and usually hoof shaped. The upper surface is grey to brown or black and forms a smooth crust. The lower pale brown surface is porous and concave. These conks are found on standing living or dead trees and on slash.

Fomitopsis pinicola Red Ring Conk, brown crumbly rot

Host: many conifers, usually a saprot but can become a heartrot.
Damage: causes brown crumbly rot, very common on dead trees, a scavenger kind of fungus. Prolific fruiting.

Ganoderma applanatum White Mottled Rot

Host: commonly deciduous trees but also found on coniferous species. In B. C.: maple, alder, birch, beech, poplar, willow, amabilis and grand fir, white and Sitka spruce, Scots pine, Douglas-fir, mountain and western hemlock, and western redcedar.
Damage: important decay of dead trees but may enter wounds of live trees causing extensive damage.

Sapwood Rots:

These fungi attack dead wood primarily, such as sapwood that has been killed by cankers, or dead trees.
Cryptoporus volvatus gray sap rot, pocket fungus

Host: primarily Douglas-fir killed by fire or beetles
Damage: very common on dead Douglas-fir. Conks are annual, leathery and pouch-like. Decay is a brown rot.

Gloeophyllum sepiarium

Host: most conifers, several deciduous species, associated with fire-killed trees and slash
Damage: brown cubical sap rot, conk has gill-like structures, is annual, leathery and upper surface is zoned and rough.

Hirschioporus abietinus

Host: many conifers, primarily a saprot, sometimes causes a heart rot in living trees
Damage: causes a white pitted saprot, conks are small, leathery, produced on dead trees, upper surface zoned, light gray.