I was inspired to write this Daily Bucket by a question that OD posed in one of my previous buckets about our local mushroom show. She posted a photo of a tree with bright orange Chicken of the Woods brackets and wondered if the presence of fungi like that on a tree means that the tree is not in good health. A variant of this question that I have heard as well is: “Is it true that if you see a mushroom/fungus growing on a tree, the tree is sick and will die?”
As you might have guessed already, there is no simple answer to the question. It might or might not be true depending on three main variables: 1. The genus or species of mushroom/fungus, 2. the genus or species of the tree, and 3. the state of the tree’s general health, including having physical wounds to its roots or trunk.
Given the status of these three variables, the answer is : yes, maybe and no. Or everybody's favorite answer: “it depends.”
Below I will describe five of the more lethal fungi that infect trees and lead directly or indirectly to their demise. And yes, there are many mushrooms or fungi that do not harm or infect trees, even though they have much direct contact through their root system for example. And there are others that do latch onto trees and do some feasting on dead wood but do not kill the tree. One such popular, attractive and plentiful fungal fruiting body, the Turkey Tail (Trametes versicolor), is a great decomposer of dead plant life but not a killer.
Turkey tail is a polypore, as are four of the five fungi described below. This mean that they disperse their spores for regeneration from the many pores on its under side. (see adjoining photo.) The Turkey Tail feeds on and decomposes dead plant material that might be present even on living trees and returns much of the material’s constituents back to the forest soil. However, when the dead material on a live tree is decomposed, the Turkey Tail stops and does not typically go for the live tissue as do the more deadly ones I will describe below.
Some terminology
Here are a few terms concerning decay fungi and the processes of decay in trees, that I will refer to below.
Please note that there is variability among the scientists’ definitions of these terms but I have tried to give the broadest definition. I have included links and references are the end from which some of the statements come.
1. Decomposers — Any fungus that decomposes plant material
2. saprophytes— feed on dead and decaying plant matter
3. Parasites— attack and feed on live plants (most likely to damage or kill trees)
4. Heartwood— Wood in the inner portion of the tree, usually referring to the stem above the roots and butt of the tree. It is mostly dead wood but gives stability to the tree and thus, damage to heartwood does not necessarily kill a tree but renders it susceptible to blowdown.
5. Sapwood— The outer layers of the tree that contain the channels that move nutrients and water up into the branches and leaves and moves carbohydrates from photosynthesis down from the leaves to the rest of the tree. Decay of sapwood kills the tree by depriving it of its ability transport nutrition and water to the tree from the roots.
6. white rot— Fungi that produce white rot preferentially attack lignin within the vascular system and turn it white and fibrous. Some white rot fungi also produce bioluminescence through the breakdown of lignin.
7. Brown rot— fungi that produce brown rot attack the heartwood and breaks down its cellulose causing the inner wood to shrink, turn brown and eventually degrade into cubically shaped pieces.
Fungi can be saprophytes or parasites and sometimes both.
It is perfectly natural for fungi to feed on plant material in order to survive. Some of the decomposed material is taken in as nutrients while other parts of the decay remain in the forest or your yard contributing nutrients that enrich the soil. In the larger picture of nature, it is perfectly natural for trees to host fungi and mushrooms as they are mutually beneficial to one another over long times. In the short term, they appear harmful as they might harm trees and affect our life style and aesthetics. They kill trees in our yards, or orchards. In the long term, forests could not prosper without them.
In the case of the more deleterious mushrooms, by the time that you see them growing on trees or at their roots or the base, the fungi have already invaded the inside of the tree and roots. They have been working away on it for some time, probably years, literally eating it away from the inside.
Some pathogenic fungi to keep your eyes open for:
Ganoderma applanatum (Artist’s Conk)
Ganoderma applanatum is parasitic and saprophytic,[2] and grows as a mycelium within the wood of living and dead trees. G. applanatum is a wood-decay fungus, causing a rot of heartwood in a variety of trees. It can also grow as a pathogen of live sapwood, particularly on older trees that are sufficiently wet. It is a common cause of decay and death of beech and poplar, and less often of several other tree genera, including alder, apple, elm, buckeye and horse chestnut, maple, oak, live oak, walnut, willow, western hemlock, Douglas fir, old or sick olive tree, and spruce.
G. applanatum is one of the more popular polypores as it provides a natural canvas for artists and hence, popularly called the “Artist’s Conk.” Under its typical layered brown cap is its white or whitish surface filled by tiny pores that hold and develop its reproductive spores as shown above. This under surface can be written or drawn on and is a common medium for artists. A sharp object, including fingernails scratched across this surface leaves an indelible print once dried. There is some attractive artwork on G. Applanatum conks but most online examples are copyrighted so you will have to settle for a very amateurish “Folk art” drawing from me. Or better yet, go to this site for some real conk art from Maria Heerkens.
G. applanatum is more common on dead trees and logs. This conk attacks both conifers and deciduous of several genera, particularly beech and poplar where it can be both a parasite affecting both the heart wood and sapwood. To further illustrate this “cool conk’s” lethality, the next photos are of a blown down birch that fell across one of my favoring walking trails in a local forest. On its butt were two large G. applanatums that had been working on it for some amount of time. The final blow was a storm with strong winds and single digit temps. This birch tree had sustained extensive root and butt rot such that the tree broke off in the storm.
As you’ve seen, the Artist’s Conk has a brown, leather-like cap often covered with a multitude of reddish brown spores called condidia which are asexual spores. This fungus is one of the world’s greatest spore producers. It has been estimated that over a six month fruiting season it can produce 5 trillion spores. (That is with a T.) Even though those spores are microscopic, that many could encircle the globe if laid out end to end.
On the right you can see the dust-like spores on the top of the conks as well as those that show as a tan dust on the host tree.
The fruiting body is a perennial and will enlarge with each year’s growing season reaching to 25 inches or more across. These and the ones shown above were about 15 inches across and about 2” thick.
On an historical note, G. applanatum was instrumental in the demise of the once famous Anne Frank tree in Amsterdam that she mentions in her book. That tree gave her much pleasure when sneaking peeks out of the annex where she hid from the Nazis. You can see the original tree: Link here.
For the last several years, the tree was attacked by a particularly aggressive fungus (Ganoderma applanatum, also called "Artist's Conk" or "Artist's Bracket") which rotted the wood and undermined the tree's stability. Additionally, horse-chestnut leaf miner moth caterpillars (Cameraria ohridella) ate the tree's leaves, causing them to turn brown prematurely contributing to the fall in 2010 and fall off.
The 170 year old Horse Chestnut, weakened by the various pathogens, came down in a storm in 2010.
Armillaria (spp) (Honey Mushrooms)
The genus Armillaria is a particularly hazardous group of mushrooms, popularly known as Honey Mushrooms for their color and aroma - take a sniff.
Virtually every article I consulted on the issue of fungi that harm trees, began with Armarillia’s 40 species noting they attack timber, agricultural and ornamental plants and trees world-wide. One particularly virulent species is the A. ostoyae, which is both a parasite and a saprophyte. These fungi are highly destructive to both conifers and deciduous trees. The disease they bring is a white rot called Armillaria root rot or Oak root rot, as it is often found on oaks.
Most typically, Armillaria will attack trees that are somehow weakened by other infestations or by lack of water or nutrition. They typically spread from infected trees to uninfected trees by spreading rhizomorphs, a root-like structure that works its way through the soil until it meets new root structures in another tree. Once inside the tree they eat at its sapwood which disrupts the flow of nutrients from roots up to the tree and the carbohydrates from photosynthesis downward.
An infected tree will die once the fungus has girdled it, or when significant root damage has occurred. This can happen rapidly, or may take several years. Infected plants will deteriorate, although may exhibit prolific flower or fruit production shortly before death.
Armillaria mushrooms are often attractive and edible, having a scent of honey. Further, they are one of the white rot fungi that are bioluminescent as a byproduct of decomposing the lignin. However, if you find some growing en masse around the foot or on the roots of your tree, that is indeed a sign that your tree most likely already has Armillaria root rot and it will be difficult and very expensive to save the tree.
Check here for a brief video overview of armillaria that addresses the issue of armillaria fungi attacking and killing trees. The narrator asks the question: “are there other fungi that can prevent the destructive processes?” (Yes, there are.) The mycologist in the video describes recent research studies that have looked into this issue. The video is about 20 min. and quite well done by an experienced mycologist. You might be surprised by what a possible antidote to Armillaria root rot is.
Laetiporus (Sulphur Shelf, Chicken-of-the-Woods)
Fungi of the Laetiporus genus are among the most colorful in the forest and are found world-wide. There are two basic species of Laetiporus in Western North America: L. conifericola (conifer trees), and A. gilbertsonii- (hardwood trees, largely invading oak). There are up to 12 species in NA but Laetiporus is found around the world with a number of different species.
These orange to yellow “Sulphur shelf” fungi enter a tree as do most such fungi through a wound site. From there they will develop a Brown Rot/butt rot decay which affects the butt heart wood of both hardwood trees and conifers, degrading the the core of the tree and compromising its stability. Depending on the species, some are also white rot producers that damage the outer vascular system ultimately leading to the tree's decline.
The shelf clusters that we see on a live tree are a outward manifestation that the interior is being decomposed. These fungi are both parasitic, eating the host when it is still alive and saprobic, living on the decomposing dead wood.
Being an annual, its fruiting body, the shelf, develops in summer and fall, then dies back. Sometimes growth comes back year after year as the mycelium remains eating away at the tree core. To the extent that it is the core or heart wood being attacked, the tree will eventually become brittle, lose its flexibility and will snap off in wind storms.
When young, the fruiting body is soft and pliable with the top colored portion very suede-like. Before it hardens with age, it is considered a choice edible as the meat reportedly tastes like chicken some say and can be a satisfying meat substitute. For those interested, The Cornell Mushroom Blog has a recipe for “polypore omelet.”
Heterobasidion annosum
Heterobasidion annosum does not have a common name. I think because no one likes it. It is not pretty, it does not glow in the dark and you can’t eat it. This is the fungus shown in the title photo and is one of the most destructive fungal parasites in the forests of the temperate regions of the northern hemisphere. Thus it is extremely costly, causing losses of over 1 billion dollars per year by the North American forest industries and equally damaging and costly to forest industries in Europe and around the world. Within this range, it also attacks Christmas tree plantations at significant cost to the growers.
As a parasitic pathogen, H. annosum attacks primarily conifers and causes a white rot of tree butts and roots. Most susceptible are pines and true firs, often killed within one to three years of their infection. Less susceptible to this rot are Douglas-fir, hemlock, cedar, larch, and spruce. When these later conifers are infected, they experience some heart and sapwood decay which weakens them and renders them more susceptible to bark beetle which further injures them.
When the fungus enters the susceptible conifers it does its parasitic damage internally and underground in the butt, roots and heartwood. An infected tree might not show any external symptoms of its damage for one to three years at which time the conks emerge and half of the tree might already be dead.
Considerable research has been conducted on this pathogen world wide as it is extremely costly to wood and forest industries. Thus far, no cure or definitive treatment has been found, especially since such extensive damage is often already done by the time it is detected. However, it’s spread can be controlled by cutting down all infected trees and applying Urea and Borate solutions to stumps, although this is not without other local environmental affects. Digging up stumps is better but is a huge and expensive job.
Fomitopsis ssp. (Red Belted Polypore)
F. mounceae is one of the more common conks around the PNW and as such does a fair amount of destruction of live conifers by its action as a brown rot parasite favoring conifers but also attacking aspen. This conk is a perennial and as such continues its growth and feeding year round, both inside and out. The more layers and larger the conk is, the older it is.
As a stem rot species (heartwood rot) this polypore attacks the core of the stem. It typically leaves the vascular system intact so the tree remains live but with a dead or hollowed out core. The loss of the core heartwood leaves the tree weakened and prone to breakage in high winds. This process is clearly illustrated in the following photos taken the same day and from the same forest as the Artist Conk shown previously.
Being a heart wood parasite this F. mounceace seems to have hollowed out the heart wood of the tree, although the sapwood which was keeping the tree alive still appears viable. Note the core is hollow at least a foot or so in. This had only been down for about two weeks. Such hollowed out logs make great nests or homes for many wildlife in the forest. I am sure they appreciate the new apartments that appear after such storms.
Final comment on “tree killer Fungi”
Although this presentation depicts one of the destructive attributes of certain fungi, the world would be very different without these decomposers. Soil nutrients would have been used up long ago if not replaced by these and other decaying organisms. It is important to realize that fungi were here before trees, but they have lived together in some sort of harmony with one another and with the rest of the environment for perhaps the 385 millions of years since trees have existed. It is difficult to date fungi as they do not fossilize well.
We see these events in a very short time frame whereas nature takes the deep-time perspective. It takes decades or more for a fungus to completely decay a log such that it becomes a new and nutritious substrate for the next round of trees to flourish. Think about all the nurse logs and stumps. We are the late comers, the interlopers. Trees (and other plants) and fungi have evolved many ways to live together for the advantage of both over a multi-million year time frame. They nurture one another in a symbiosis as well as feed and house us. We have done more damage to both than either of them have done to each other or to us. The fungus — tree relationships are but one of many symbiotic relationships between organisms that sustain our natural world. Fungi might be a pain to us but they are just doing what they evolved to do.
How are your trees doing? No matter how they are at this time, you should go out and give them a hug. You don’t have to be a “tree hugger” just to give your trees a little hug of appreciation.
Please contribute your experiences with fungi and trees, especially those of you who have specific expertise in this area.
Additions and corrections are Most encouraged.
References
- en.wikipedia.org/… All about wood rot and decay
- www.energy.gov/… (White rot is most efficient decayer of lignin and it produces CO2 in the processes that feeds the fungus.
- forestpathology.org/… An informative table that shows many of the decay fungi and what they attack.
- www.americanforests.org/… From an interesting magazine story (American Forests) about how species of trees are migrating to more hospitable climes.
- /. https://en.wikipedia.org/wiki/Ganoderma_applanatum extensive coverage of the Artist’s Conk and relatively up to date.
- www.ncbi.nlm.nih.gov/… A very informative scientific review of Armillaria’s pathology.
- ipm.ucanr.edu/… U. Cal. Pest management program in formation page on armillaria.
- learnyourland.com/… a video describes Armillaria, its destructive side and how it might be addressed to reduce the adverse affects of this parasitic fungus
- bsppjournals.onlinelibrary.wiley.com/… Extensive Scientific review of H. annosum’s wide spread effects and mechanisms of action.
- uk.inaturalist.org/… Good overview of H. annosum from iNaturalist