Home

See also:
Survey of potential sapstain fungi on Pinus radiata in New Zealand
Joanne M. Thwaites, Roberta L. Farrell, Shona M. Duncan and Stephan D. Reay (Forest Biosecurity Research Council report)

Tree Decays


Forest Pathology in New Zealand No. 17

 
Based on I.A. Hood (1986)
 
 
Fig. 1 - Stem of large rimu tree (Dacrydium cupressinum) broken by wind as a result of
extensive butt heartwood decay caused by Armillaria sp.
 
Introduction
This leaflet describes decays of sapwood and heartwood in standing or fallen trees. Rots of
stacked logs or processed timbers are excluded. 
Sapwood is the outer wood in which, in the growing tree, sap flow occurs. It contains both living
and dead cells. Decay of sapwood is known as sap rot. Heartwood is the wood, sometimes darker
in colour, present at the centre of an older tree. It contains no living cells, but may have natural
preservative substances which provide resistance against most decay fungi. Trees in which the
heartwood is decayed are said to have heart rot. 
 
Causal organisms
Wood decay is caused by a wide range of fungi. The major decay fungi of living trees are listed
in Tables 1 and 2. Most of these fungi also occur on dead trees, stumps, or logs of their hosts,
and even in living trees they decay only the dead heartwood. However, a number are parasitic
(indicated by an asterisk in Table 1) and may invade live tissues. 
 
Type of injury
Decay and deterioration in strength and quality of sapwood or heartwood in living or dead,
standing or fallen trees. 
 
Diagnostic features
Early and intermediate decay (dozy wood): Early stages of decay are not always easy to detect
without laboratory examination. Comparisons should be made with healthy wood. Indications
may be given by:
• Red, brown, or white discoloration or staining. (Dark blue or black wedge-shaped stains are
caused by non-decay fungi which reduce the visual quality but not the strength of wood.)
• A decrease in hardness (testable by prodding with sharp instrument), and relative ease of
cutting during sawing (cut faces have a roughened texture). 
• An even fracture without splintering when broken. 
• Thin, dark coloured "zone lines" present in wood. 
• Bark readily separates from wood (white fans of fungal mycelia may lie between). 
• A mushroom-like odour.
Advanced decay: Well-decayed wood is indicated by changes in colour, form, weight, and
strength. Field identification of the causal fungus is sometimes possible at this stage, from a
consideration of the following points:
• Presence of identifiable fungal fruiting bodies (not necessarily conclusive since they may be
produced by fungi other than those causing the rot).
• Occurrence of a distinctive rot pattern, characteristic of a specific fungus, which tends to be
the same regardless of host. Examples include white rots (Fig.2), brown, cubically-cracked
rots (Fig. 3), and "pocket" rots in which the decayed wood is traversed by a system of
cavities (Fig. 4, 5, 6).
• Restriction of decay to a particular habitat. For instance, many rot fungi only occur in dead
trees, stumps, or logs, while others also decay living trees (Tables 1, 2).
 

Fig. 2 - White rot in log of tawa (Beilschmiedia tawa) caused by Irpex brevis. Many zone lines
have been produced.
 

Fig. 3 - Brown cubical rot in kauri (Agathis australis) produced by Phaeolus schweinitzii.
 

Fig. 4 - Fruiting bodies and charactaristic honeycomb decay caused by Polyporus catervatus
taken from heartwood in the butt region of rimu (Dacrydium cupressinum). This decay loads to
wind- throw or stembreak of overmature trees.
 

Fig. 5 - White rot of hinau (Elaeocarpus dentatus) with pockets containing mycelium of
Phellinus wahlbergii.
 

Fig. 6 - Pocket heartrot of totara (Podocarpus totara) produced by Phellinus lloydii. This decay
is known as kaikaka.
 
Hosts
All tree species are subject to fungal decay, but individual fungi vary in their ability to attack
different hosts. Some fungi are capable of causing rots in many different hosts, while others are
confined to particular groups, or even to single species. A number of decay fungi are largely
restricted to "hardwood" or "softwood" trees, terms which do not necessarily refer to wood
toughness. Hardwoods are broadleaved trees such as tawa, kamahi, eucalypts, and oak;
softwoods are coniferous trees with needles or scale leaves such as rimu, kauri, pines, and
larches. Several fungi are found mainly on introduced hosts, suggesting that they themselves
may have been introduced to this country (e.g., Amylostereurn areolatum, Table 1). 
 
Distribution
Decay fungi are found in natural and planted forests throughout the country, and also occur
wherever woody plants are grown, such as in gardens, orchards, and on farms. Native forests
support the greatest number of species of decay fungi. Detailed distribution ranges of particular
rot fungi are, in general, poorly known but many appear to be widespread throughout New
Zealand. Some species are restricted by the limited distribution of their natural hosts. For
example, Heterobasidion annosum (Table 1) and Phaeolus schweinitzii (Table 2) are not found
outside the natural range of Agathis australis (kauri), and Grifola colensoi (Table 2) is confined
to localities where Nothofagus species (native beeches) occur. On the other hand, species such as
Fomitopsis hemitephra (Table 2, Fig. 18) occur on hardwoods in both beech and
podocarp/hardwood forests. 
 
Disease development
Wood decay fungi reproduce by means of spores released into the air from fruiting bodies. These
fruiting bodies may take the form of discs, cups, brackets or shelves, crusts, toadstools, or jelly-
forms. Decay begins when airborne spores land and germinate on recently dead or fallen trees, or
on wood surfaces freshly exposed by the wounding of living trees. Entry wounds or openings are
created by machines or failing trees during logging or thinning operations, destructive winds,
fires, heavy snowfalls, physiological stresses induced by drought or cold, and animal damage
(e.g., chewing or bark stripping by possums or kaka). Fungi can also invade trees through their
roots or by first colonising dead branches or tops. 
 
Decay fungi grow within wood in the form of microscopic branching threads, or hyphae, known
collectively as a mycelium. As mycelia of different fungi extend, they come into contact with
each other. If antagonisms occur, thin black zone plates form in the wood along the planes of
contact between mycelia. These are visible as thin lines in cut surfaces and indicate the sphere of
activity of each mycelium. Zone plates may also develop parallel to freshly cut surfaces and
protect the mycelium from excessive drying. With time, successions occur, one fungus replacing
another as wood decay proceeds. 
 
The hyphae of wood decay fungi secrete enzymes as they grow. These destroy small sections of
the wood cell walls, which consist primarily of cellulose and lignin. The mycelium is thus able to
penetrate deeper into the wood, and in the process obtains nutrients from substances produced
during the breakdown of the cell walls. Because each species of decay fungus secretes a
characteristic complement of wood-destroying enzymes, distinctive decay patterns are produced.
Thus, brown- rot fungi (Fig. 3) destroy the cellulose component of wood cell walls, but are
unable to degrade the lignin. The resultant decay has a structured appearance and is dark in
colour due to the high proportion of lignin present. White-rot fungi are able to destroy lignin as
well as cellulose, and the resultant decay is paler in appearance and less structured (Fig. 2). 
The process of decay is governed by a number of environmental factors. Like all organisms,
decay fungi require an adequate water supply. Decay will not normally occur or be sustained in
wood with a moisture content maintained below 20% (oven dry weight basis), although these
conditions will not necessarily kill the decay organism once it has become established. In
addition, decay fungi are aerobic and will not grow at low oxygen or high carbon dioxide
concentrations. Most decays are thus also inhibited by a high wood-moisture content (exceeding
about 70%), because this excludes air from the wood cells. 
 
In living trees deposits of toxic chemicals that inhibit most decay fungi normally protect the
heartwood from rotting. In many trees heartwood decay is also prevented by a naturally
occurring high moisture content (e.g., in excess of 80% in species of Podocarpus compared to
only 40-45% in Pinus radiata). Nevertheless, a limited number of decay fungi are able to tolerate
these conditions and produce characteristic heart rots in their living hosts. Decay in the sapwood
is usually prevented by the natural resistance responses of the living cells (e.g., resin flow in
softwoods, following wounding) and by a high moisture content (exceeding 90% in most trees).
If decay is present it is generally localised at sites of wounding or stress. However, when a tree
dies or fails, the sapwood rapidly begins to decay, whereas the heartwood initially remains
relatively resistant to rot fungi. The decay of fallen trees is governed by their rate of drying
which, in turn, is controlled by combinations of the following factors: tree species; stem
diameter; proportion of sapwood; length of stem in ground contact; extent of uprooting; amount
of shade cover; degree of stem shatter; location, and time of year. 
 
Even though rots destroy wood, crown health is not usually affected because most of the decay
fungi are saprophytes and feed only on dead tissue of living trees. However, some are parasitic
fungi and may extend their activity into the still living sapwood. A limited number are capable of
invading the host directly, without the need for wounding. These fungi do impair tree health and
in severe cases even kill the host. Severe root rotting may also affect crown health and tree
stability. 
 
Economic importance
Decay losses result from wood destruction, and from uprooting or breakage of rot-weakened
trees during strong winds (Fig. 1). The most extensive decay damage is found in old growth
beech or podocarp/hardwood forests, because rots are more prevalent in older trees (Fig. 7). Now
that logging in these native forests has declined, decay damage has become economically much
less important. Harvesting is currently prohibited in State native forests, apart from limited
logging in certain, specified areas, but felling is still permitted on private land. In these situations
losses may result from the rapid development of destructive sap rots, accompanied by insect
tunnelling, if fallen trees are not retrieved quickly. 
 
 
Fig. 7 - Extensive heartwood decay at the base of a large silver beach tree (Nothofagus menziesii) 
 

Fig. 8 - Destruction of timber by a brown cubical heart rot in larch (Larix decidua) following
damage to a residual tree during thinning operations.
 
In forests of introduced tree species, standing trees are cut at a comparatively early age, and
losses from decay are usually uncommon. However, significant heart rot has occurred in older
stands of Larix decidua as a result of damage caused by earlier pruning and extraction thinning
operations (Fig. 8). Decay associated with dead branches and pruning wounds is also a feature of
some Eucalyptus stands. Severe storms periodically cause extensive windthrow in plantation
forests, and as in native forests, immediate salvage logging is necessary to avoid losses from
stain and decay fungi or insect activity. In recent years, windthrow-related losses have occurred
at Golden Downs State Forest (1968), Ashley, Hanmer, Eyrewell, and Balmoral State Forests
(1975), and Kaingaroa State Forest (1982).
 
In any native forests where salvage or selective logging is still practised, careful felling and
extraction techniques will minimise damage and decay in residual trees. In plantations of
introduced softwoods, control measures are not necessary, except that scar damage should be
kept to a minimum if extraction thinning is carried out in stands of Larix decidua. Prevention of
decay during pruning of Eucalyptus species will be dealt with in a separate leaflet. Windthrown
trees should be salvaged as quickly as possible. If delays are unavoidable, water sprays or water
immersion should be used to maintain a high moisture content and reduce the incidence of
degrade.
 
 
Fig. 9 - Fruiting bodies of Armilleria limonea.
 

Fig. 10 - Fruiting bodies of Coltricia aureofulva.
 

Fig. 11 - Fruiting bodies of Cyclomyces tabacinus.
 
 
 
Table 1 - Decay fungi of both living native and introduced trees (* Indicates parasitic fungus.)

Name

Synonyms

Associated rot-type and comments

FUNGI DECAYING BOTH HARDWOODS AND SOFTWOOD

Armillaria limonea (Stevenson) Boesewinkel*	(Armillariella limonea)	White, large-pocket heart-butt rot; root disease of introduced trees (Leaflet 4; fig. 9).
Armillaria novae-zelandiae (Stevenson) Herink*	(Armillariella novae-zelandiae)	White, large-pocket heart-butt rot; root disease of introduced trees (Leaflet 4).
Chondrostereum purpureum (Persoon ex Fries) Pouzar*	(Stereum purpureum)	White rot; a fatal wound parasite of fruit trees (silver leaf disease).
Coltricia aureofulva (Lloyd) Cunningham	(Polyporus aureofulvus)	White pocket heart rot with orange zone lines (Fig. 10).
Cyclomyces tabacinus (Montagne) Patouillard*	(Inonotus tabacinus)	Yellow pocket heart-sap rot of damaged trees (Fig. 11).
Ganoderma applanatum (Persoon ex Wallroth) Patouillard	(Elfvingia applanata) (Fomes applanatus)	White heart rot.
Ganoderma mastoporum (Léveillé) Patouillard	(Elfvingia mastopra) (Fomes mastoporus)	White heart rot (Fig. 12).
Grifola rosulata (Cunningham) Cunningham	(Polyporus rosulatus)	Brown cubical heart rot in Larix decidua.
Gymnophilus junonius (Fries) Orton	(Gymnopilus spectabilis) (Pholiota spectabilis)	On living Weinmannia racemosa and base of living Eucalyptus species; on stumps, Pinus species (Fig 13).
Junghuhnia vincta (Berkeley) Hood*	(Chaetoporus vinctus) (Poria vincta) (Rigidoporus vinctus)	White rot; root disease of trees in shelterbelts and plantations in the Bay of Plenty.
Gloeocystidiellum sacratum (G.Cunn.) Stalpers & P.K.Buchanan*	Peniophora sacrata G.Cunn.; Phanerochaete sacrata (G. Cunn.) J. B. Taylor; Amylostereum sacratum (G. Cunn.) Burds.; Dextrinocystidium sacratum (G. Cunn.) Sheng H. Wu.	Peniophora root and stem canker. White heart-sap rot; root disease especially of Pinus species (Leaflet 3).
Phellinus scruposus (Fries) Cunningham	(Fomes scruposus)	White heart rot.
Polyporus catervatus Berkeley (Tyromyces catervatus)	(Tyromycetes catervatus)	Pocket "honeycomb" heart- butt rot, especially of Dacrydium cupressinum (Fig. 4).
Pycnoporus sanguineus (Linneus ex Fries) Murrill	(Coriolus sanguineus) (Pycnoporus coccineus)	(White rot; noted on living Knightia excelsa (Fig. 14).
Schizophyllum commune (Fries) Fries*		Noted as a weak wound parasite on Sophora microphylla, Pyrus malus.
Trametes versicolor (Linneus ex Fries) Lloyd*	(Coriolus versicolor) (Polystictus versicolor)	Noted as a weak wound parasite on Betula pendula and fruit trees (Fig. 15).

FUNGI DECAYING HARDWOODS ONLY

Agrocybe cylindracea (de Candolle ex Fries) Maire*	(Agrocybe aegerita) (Agrocybe parasitica)	Heart rot; may also invade sapwood (Fig. 16).
Phellinus robustus (Karsten) Bourdot & Galzin	(Fomes robustus)	Heart rot.
Piptoporus portentosus (Berkeley) Cunningham	(Polyporus eucalyptorum) (Polyporus portentosus)	Brown cubical heart rot of Nothofagus species; also on living Eucalyptus species

FUNGI DECAYING SOFTWOODS ONLY

Amylostereum areolatum (Fries) Boidin*		White sap rot introduced conifers only; parasitic transmitted by Sirex wood wasp (Forest and Timber Insects in New Zealand No. 20).
Heterobasidion annosum (Fries) Brefeld*	(Fomes annosus) (Fomitopsis annosa)	Known only on Agathis australis (occasional sap rot of live tree) and Pinus taeda logs; taxonomically distinct from the more parasitic, Northern hemisphere form.
Stereum sanguinolentum (Albertini & Schweinitz ex Fries) Fries*	(Haematostereum sanguinolentum)	Yellow stringy heart rot (and occasional wood sap rot) of introduced conifers (e.g., Larix decidua)

 

Fig. 12 - Fruiting bodies of Ganoderma mastoporum in old stump.
 

Fig. 13 - Fruiting body of Gymnopilus junonius in living kamahi (Weinmannia racemosa).
 
 
Fig. 14 - Fruiting body of Pycnoporus sanguineus from beneath.
 
 
Fig. 15 - Fruiting bodies of Trametes versicolor.
 
 
Fig. 16 - Fruiting bodies of Agrocybe cylindracea in living tawa (Beilschmiedia tawa).
 
 
Fig. 17 - Fruiting body of Piptoporus portentosus from living red beech (Nothofagus fusca).
 

Table 2 - Decay fungi of living native trees only

Name

Synonyms

Associated rot-type and comments

FUNGI DECAYING BOTH HARDWOODS AND SOFTWOOD

Bondarzewia berkeleyi (fries) Bondartsev &Singer	(Grifola berkeleyi) (Polyporus berkeleyi)	White butt rot.
Fomitopsis hemitephra (berkeley) Cunningham	(Fomes hemitephrus) (Heterobasidion hemitrphrum)	White heart rot with orange zone lines of hardwoods and occasional softwoods (Fig. 18).
Phellinus lloydii (Cleland) Cunningham	(Fomes lloydii)	Pocket heart rot; "kaikaka" of Podocarpus totara, P. hallii, (Fig. 6).
Phellinus senex (Nees & Montagne) Imazeki	(Fomes senex)	White pocket heart rot of hardwoods and occasionally softwoods.
Phellinus wahlbergii (Fries) Reid	(Fomes hamatus) (Phellinus laurencii) (Phellinus zealandicus)	White pocket heart rot; cavities with brown mycelium; occurrence in softwoods infrequent (Fig. 5, 19).
Pholiota adiposa (Fries) Kummer		Heart rot in Hoheria angustifolia.
Poria undata (Persoon) Bresadola	(Rigidoporus vitreus)	White pocket rot with small, fleck-like cavities of hardwoods and occasionally softwoods.
Tyromyces guttulatus (Peck) Murrill	(Polyporus guttulatus)	In living Ixerba brexoides.

FUNGI DECAYING HARDWOODS ONLY

Auricularia polytricha (Montagne) Saccardo	(Hirneola polytricha)	On dead limbs, sometimes descending into the living trunk.
Coltricia laeta (Cooke) Cunningham	(Fomes cuneatus) (Fomitopsis cuneata) (Heterobasidion tasmanicum)	White heart rot (Fig. 20).
Fomitopsis tasmanica (Berkeley) Cunningham	(Fomes cuneatus) (Fomitopsis cuneata) (Heterobasidon tasmanicum)	White heart rot (Fig. 20).
Grifola colensoi (Berkeley) Cunningham	(Polyporus colensoi)	Brown cubical butt rot specific to Nothofagus spp.
Hymenochaete corticolor Berkeley & Ravenel		Pocket rot of Nothofagus fusca.

FUNGI DECAYING SOFTWOODS ONLY

Phaeolus schweinitzii (Fries) Patouillard

(Coltricia scweinitzii)

Brown cubical butt rot known only on Agathis australis (Fig. 3).

 
 
 
Fig. 18 - Fruiting bodies of Fomitopsis hemitephra in living kamahi (Weinmannia racemosa).

 
Fig. 19 - Fruiting bodies of Phellinus wahlbergii.
 
 
Fig. 20 - Fruiting body of Fomitopsis tasmanica.
 
Bibliography
Butcher, J.A. 1974: A practical guide to fungal damage of timber and wood products. New
Zealand Forest Service Information Series No. 65.
Cunningham, G.H. 1963: The Thelephoraceae of Australia and New Zealand. New Zealand
Department of Scientific and Industrial Research Bulletin 145. 
Cunningham, G.H. 1965: Polyporaceae of New Zealand. New Zealand Department of Scientific
and Industrial Research Bulletin 164. 
Gilmour, J.W. 1966: The pathology of forest trees in New Zealand. New Zealand Forest Service,
Forest Research Institute, Technical Paper No. 48.
Hood, I.A. 1987: Tree decays. New Zealand Forest Service, Forest Pathology in New Zealand
No. 17.
 

Compiled: 1986.