Factoring wood decay into risk
assessment
Matteo Garbelotto
U.C. Berkeley
The ability to decay wood
• Wood is decayed thanks to a complex set of
enzymes that are capable of degrading
cellulose, hemicellulose, lignin, and pectins
• The “masters” of wood decay are the fungi,
and there is good evidence that ligninolitic
enzymes have been transferred horizontally
from the fungi to insects, allowing them to
create a habitat favorable to the progeny
Wood decay is an essential ecological
component of terrestrial ecosystems
• It is necessary to remove the physical mass of
woody plants to leave room for regeneration
• It is a key element of the C cycle
• It is a process that increases biodiversity
• It is a process that fits the continuum between
endophytism, saprophytism, and
pathogenicity
Injuries and damage property in
an urban setting
Timber losses
Hazards, such as windthrows in
recreational settings
Disease and mortality, leading to a loss in
the productivity of the ecosystem
Wood decay is:
• The primary agent responsible for tree failure
Other factors leading to tree failure
• Genetic defects
• Height : diameter ratio
• Shallow soils
• Metereological events such as tornados,
windstorms, heavy snow
• etc
Wood decay is a complex process
• It is the result of an active, complex, and changing
community of organisms
• White rots, brown rots, soft rots, yeasts and
bacteria are all involved in the process, with each
group represented by multiple species in a single
tree
• At times, decay organisms compete with one
another (antagonistic interaction), but at times
their interaction is synergistic: e.g. Armillaria
infection facilitates root infection by Phaeolus
schweinitzii
Gaseous phase in wood as a major
driver of decay
• In trees, there is an inverse relationship between
moisture content and gaseous phase
• Decay agents cannot function in anaerobic conditions
(e.g sapwood of healthy trees), neither can they
function when the wood is too dry
• In general, any event (disease, mechanical damage)
that allows for an increase in the gaseous phase, may
potentially trigger a decay process
• Heartwood has a lower moisture content than
sapwood, hence intrinsically, it is more susceptible to
decay. Phenolics and other radicals accumulate in
heartwood to prevent or slow down decay processes
da Rayner and Boddy (1988)
Heartwood
Sapwood
Carbon loss
Temperature is a
secondary driver of
decay rates, with
stronger effects on
smaller trees
Temperature
Infection strategies
• 1- Vegetative growth: the organism reaches
the substrate with massive structures such as
cords or rhizomorphs, sometimes trough
mycelium within roots that are grafted or in
contact: Hypholoma fasciculare, Armillaria
spp, Phellinus weirii.
• As a consequence, if infection of substrate is
successful, then decay can be very aggressive.
Infection strategies
• 1- Vegetative growth: the organism reaches
the substrate with massive structures such as
cords or rhizomorphs, or sometimes trough
mycelium within roots that are grafted or in
contact: Hypholoma fasciculare, Armillaria
spp, Phellinus weirii.
• As a consequence, if infection of substrate is
successful, then decay can be very aggressive,
However if decay is effected through a
pathogenic infection of a live host
• Be aware that there is an exploratory phase
and an exploitative phase.
• E.g. rhizomorphs may be present on roots, but
if in exploratory phase, there is no decay
• Events such as depauperation of nutritional
substrates, or stress induced on live plants
(such as flooding) will trigger the exploitative
phase and start the decay
Signs can be ambiguous
• Rhizomorphs may be
present but decay
absent if in exploratory
phase
Fruitbodies and mycelial fans indicate
infection is ongoing. Often large number
of basidiomes may be indicative of advanced
decay
Infection
Via spores, either airborne or vectored by insects
Normally decay of the heartwood
“Evasion”strategy: fuiting occurs on “non-functional” sapwood
Infection/invasion
Rhyssa persuasoria
Evasion
Infection through spores (2)
Spores start an endophytic phase in
infected tree that may last decades
When conditions become favorable
to decay due to senescence of tree,
or due to increased gaseous phase
because of disease, decay starts
Echinodontium tinctorium
Heterobasdion occidentale
Anulohypoxylon thuorsianum
Presence of fruitbodies indicates
decay is advanced
Stereum sanguinolentum
wound rot fungi
marciumi e carie
White rot with a reddish tinge, fibrous
Fruit bodies
Rhizina undulata Ascomycete
pine fire fungus
(needs >38 C)
Mortality of seedlings
Staining of wood
Mycelial cords
Resinosis
Two mechanisms of “defense”: CODIT and adaptive growth
CODIT
Important Decay Evaluation Factors for
Risk Assessment
• 1 What general type of decay
• 2 Where is the decay, can it move from one part
to another
• 3 Is it infecting the roots, any symptoms
• 4 Is it a heartrot, a saprot, or a canker rot
• 5 Can we predict the size and shape of the decay
column
• 6 Is there a combo of decay agents
• 7 Is the decay agent aggressive
• 8 Is it a fast spreading decay ( high decay rates)
1-White vs. Brown vs. Brown-Cubicle
vs. Soft rots
Even if they look “ different” and the perception of loss of strength is obvious for the
brown cubicle rot, risk is extremely similar for all types of rots. Soft rot normally is
associated with either white or brown rot. So all three need to be taken equally
seriously
Stereum gausupatum
2,3-Top rot, butt rot,
root rot
• Root and butt rots pose
two substantial greater
problems: they affect the
health of the tree and/or
Trametes versicolor
they affect its stability:
their confirmed active
presence needs immediate
attention
• There may be no
symptoms (false security)
because trees can do well
Armillaria spp.
with 40% of roots
• Top rots can often be dealt
with an “arboricultural”
approach, unless canker
rot or combined rot
Decay agents by location of decay
(B>C>A in terms of danger)
• A Top rots: Stereum hirsutum, Schizophyllum comune,
Daedalea quercina, Daedalopsis confragosa, Inonotus
hispidus, Trametes hirsuta, Trametes versicolor
• B Butt and root rots: Ganoderma australe,Ganoderma
resinaceum. G. lucidum, Inonotus dryadaeus,Phellinus
torulosus, Phellinus ignarius, Fomes fomentarius,Meripilus
giganteus, Rigidoporius ulmarius, Kretzschmaria deusta,
Sparassis spp. , Phellinus gilvus, Laetiporus sulphureus
• C “Renaissance Rots”: Ganoderma applanatum,
Perenniporia fraxinea, Fomitoporia punctata, Polyporus
squamosus, Laetiporus sulphureus
Top rots can affect success of cicatrization (healing) of pruning cuts
4 Heartrot, saprot, canker rot
• Heartrots: they are constitutionally associated with age: assume
older and larger trees have some level of heartrot. The larger the
tree the higher the chance it has hr. If hr is in the center of stem,
there may be no symptoms, but stability may be compromised. It
may manifest itself through fruit bodies or wetwood. Rate of
advancement affected by chemistry of hw and by growth rate
• Saprots: normally associated with reduction plant vigor, decline of
limbs in portion affected. Often triggered by traumatic event,
wounds, or disease that increase gaseous phase. Advancement rate
affected by response of plant and growth rate
• Canker rots: some species, notably in the genera Phellinus,
Inonotus, Fomitoporia and Fomitopsis can decay both the
heartwood and sapwood
5- Can we predict size and shape of
decay?
• Partial decay of hw
plus wound damage
with fruit body. This
is a very common
situation: if wound
small and healed, and
tree healthy, this
situation can persist
without tree failure
for a long time
5- Can we predict size and shape of
decay?
• Heartrot nicely
positioned at the
center of the stem
with most of
sapwood still
functional. This is also
a “low risk” situation
5- Can we predict size and shape of
decay?
• Heartrot nicely
positioned at the
center of the stem
with most of
sapwood still
functional but root
infection pathway is
known. Risk of failure
becomes high
5- Can we predict size and shape of
decay?
• Heartrot
asymmetrical with
respect to crosssection of stem, or
encroaching
sapwood. Risk of
failure becomes high
6 Is there a saprot-heartrot combo?
• As stated earlier, large trees have a high
frequency of heartrot, so core of stem is often
decayed and tree becomes a hollow cylinder
• Mechanical injury or any disease affecting the
cambial layer will cause damage allowing for
gaseous phase to increase in the sapwood
• When saprot fungi fruit, it means significant
decay of sapwood has occurred
• No heartwood and decayed sapwood=tree failure
e.g. Sudden Oak Death
Large oak with
heartrot
Saprot
Heart
rot
Tree failure
Saprot triggered
SOD infection
Heart
rot
7 Aggressive decay agents
• Some species can bypass the “walls” of
defense put up by by the host, for instance
canker rots
• E.g. Ganoderma applanatum and G.
resinaceum cause similar infection, but the
latter can bypass the response of the host
8 Rate of decay varies among fungi
• High rate: Coriolus,
Lentinulus,Oudesmaniella, Panus,
Polyporus,
Pycnoporus,
Xylobolus,
Fomitopsis,
Laetiporus, Stereum
A complete Risk Assessment requires
• Visual evaluation of physical structure of trees, including signs of
decay: size, diameter, height:diameter ratio, size of canopy,
wetwood, basidiomes, temperature of area
• Physical location: neighboring trees, people and vehicular transit,
property
• Symptoms of disease or advanced decay such dieback, reduced
growth rate, chlorotic foliage are very important. But also disease
as a trigger of decay
• Determination of fungi involved is important to predict risk: fungi
that can spread from stem to butt, or from butt to roots, canker
rots, aggressive species: these potentially help redflag the tree as a
high risk tree
Same fungus (Fomitiporia punctata),
two locations
Risk limited to branch
Risk involving all tree
Is it easy to ID decay fungi?
• Fruiting can be ephemeral, tardive, only on
some hosts
• Fruitbodies can be very similar, you will miss
all species that are not fruiting
• DNA based assay at UCB is gold standard and
is now free www.wooddecay.org
By submitting samples you will help
build up database, which will help to
• Understand true role of decay species on
various hosts, e.g. we have already
determimed Hericium spp are important
players even if they do not fruit, and they
appear to go through an endophytic phase,
Laetiporus sulphureus more important than
previously thought
• Identify fungal species associated with high
frequency of failures
Example 1: Eucalyptus
Laetiporus sulphureus
• If you see these two
fungi fruiting, or if the
DNA test from the root
collar comes back
positive for these two
species: the risk a
Eucalyptus will fall is
imminent, independent
of tree architecture.
Tree has “no” roots
Phellinus gilvus
Example 2: Jack London Oak: serious issues,
failure of entre tree not imminent
Branch declining,
significant saprot, but
50% diameter still healthy
Portion had failed and Fomitiporia
was IDed. Risk of failure of this limb
is high: increase fenced area
Healthy with
presence of
endophytic
decay fungi
(towards
cottage)
Base healthy, no decay
agents identified
Thank you!
Submit your decay samples associated with
failures, and be part of the solution
www.wooddecay.org