Shelf Fungus Diversity and Tree Health at the Morgan Arboretum

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A great diversity of shelf fungi can be seen on this rotting log


The importance of shelf fungi in the St-Lawrence lowlands

Polypores (also known as Shelf fungi and Bracket fungi) are found across North America, anywhere woody plants are present (Gilbertson, 1980). They usually grow on fallen logs, stumps, dead branches and even living trees whose bark has been breached and begins to decay (Roberts and Evans, 2011). They have a wood-like, almost leathery texture, and produce spores under their caps. Most of them are wood-rotting and therefore inflict serious damage to their hosts (K. McKnight and V. McKnight, 1987). Polypores that degrade hardwood are a problem for the lumber industry, as they lead to economic losses. However, bracket fungi are of great importance to the St-Lawrence lowlands ecosystems. Indeed, they recycle carbon by degrading cellulose from the tree bark and returning it to the atmosphere. They also allow old trees to weaken and fall to the ground, where they decompose and become important components of the soil. This allows young healthy trees to take their place, as part of the forest regeneration process. Moreover, polypores are crucial to wildlife, as they provide habitat for various species. Birds nest in the cavities they form and arthropods as well as small amphibians find shelter within their fruiting bodies (Gilbertson, 1980). Shelf fungi are very diverse, and we observed many genus during our research project in the Morgan Arboretum. Turkey Tail, Redbelt, Hen-of-the-Wood and Dryad Saddle are among the most abundant and noticeable types of fungi we encountered (K. McKnight and V. McKnight, 1987).

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Clockwise; (starting at top left) Turkey Tail, Hen-of-the-Wood, Dryad Saddle, and Redbelt fungi

Vulnerablity of trees to environmental factors

Forest composition fluctuates in response to changes in climate as well as different nonnative biotic stressors such as diseases, pests and invasive plants. The association of two or more of these factors can exacerbate population declines in some tree species as well as hinder the growth of others (Fisichelli et al., 2014).
Certain trees exhibit a higher vulnerability to these ecological strains than others. A particularly striking example is the American beech tree, Fagus grandifolia, which is plagued by beech bark disease. This blight is caused by beech scale, Cryptococcus fagisuga, which attacks bark and renders it vulnerable to fungi infestation. The invasion of the wood by fungi of the genus Nectria is deadly to the tree (Houston and O’Brien. 1983).

The disease has severely impacted the composition of North American hardwood forests, where the beech tree is a founding species. The decline in beech tree populations is detrimental to certain species and therefore alters biodiversity (Cale et al., 2013).

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A fallen beech tree with Polypores

The effects of shelf fungi on trees

Trees, regardless of the species, are vulnerable to fungal diseases when their protective outer bark layer is breached. The wound may form due to insect pests who consume the bark or use stylets to access nutrients deep within (for example, sugar maple sap), or animals who scratch the surface, peck it or feed off of it. Humans tend to carve their initials into bark for amusement purposes or expose the bark when trimming the tree and breaking off branches. Once the bark is damaged, the fungus’s spores have an entryway into the woody internal flesh and begin to thrive (Fogal 2006).

As it is extremely pervasive, it is impossible to clear a tree of a fungal infection. This is due to fungi’s composition of filamentous fibers called mycelium, which provide strength and stability. Mycelium hook onto the fibers of the wood and feed off it. By secreting enzymes, they break down wood fibers into cellulose and lignin components, which results in the degradation of the timber. From the wound, the fungus spreads internally and rots the inside of the tree. New cracks on the outside of the tree appear and allow entry for more fungi of the same or different species. The dead tree may remain standing or fall, but either way, the fungus will continue to thrive and work as a community to decompose it until there is nothing left but decayed matter (Ross D.R., n.d)

Our project

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Map of the Morgan Arboretum showing the two study sites, characterized by dominant forest type

Within the Morgan Arboretum, we conducted half of our research in the sugar maple stands and half within a mixed beech and red maple forest (as there are no pure beech stands in the Arboretum). In total, we located 40 trees of the American beech and sugar maple species that bore shelf fungi. Our research spanned three weeks, during which we made two trips to the field. On Monday October 5th, we studied 20 standing or fallen sugar maple trees for shelf fungal growth. On Monday October 19th, we inspected shelf fungus specimens on 20 American beech trees.

Upon venturing off the path, all five of us walked in different directions to allow an unbiased selection of our sample trees and to increase the variety of our outcomes. Every time we located an infected tree or log, we tied a pink marker around it to avoid repetition. Then, in an Excel spreadsheet on our portable tablet, we recorded the species, color, average diameter, and abundance of the fungi. We also assessed the tree’s health through the following criteria: approximate percentage of leaves, bark health (presence and abundance of cracks, peeling, scars, rot, etc), general health of the tree (fallen, standing, or diseased), and presence of beech bark disease.

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Pictures must be taken at several different angles to help with identification

A selection of fungi guides, including A Field Guide to Mushrooms: North America by Kent H. McKnight and Vera B. McKnight and The Book of Fungi by Peter Roberts and Shelley Evans, were of great help in identifying species of shelf fungi found in the Morgan Arboretum. The team’s field knowledge, coupled with our photographic evidence, enabled us to discern the color, shape, texture, size, and distribution of the shelf fungi. Referring to the literature, armed with our data, we then successfully classified the specimens. However, identifying fungi is no easy task due to its vast diversity and many resemblances between certain species of shelf fungi like Turkey Tail and the Multicolor Gill Polypore. Photographing the fungi from many angles, including the underside, gives a whole new perspective on each fungi and helps in the identification of the species.

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Flagging tape was used so that trees were not counted twice and to promote our twitter account

Our analysis of the data collected reveals interesting trends between different varieties of shelf fungi and their impact and relationship with the sugar maple and American beech. We determined that there is a greater diversity of shelf fungi on American beech trees as compared to sugar maple trees. This raises questions about how fungi affect the health of trees, given that the American beech trees in the Morgan Arboretum are generally in poorer health than the sugar maple trees.




Cale J, McNulty S, Teale S, Castello J. March 2013. The impact of beech thickets on biodiversity. Biological Invasions. [accessed 24 Oct 2015]; 15 (3): 699-706. http:// link.springer.com/article/10.1007/s10530-012-0319-5/fulltext.html doi:10.1007/ s10530-012-0319-5.

Fisichelli N, Abella S, Peters M, Krist Jr. F. September 2014. Climate, trees, pests, and weeds: Change, uncertainty, and biotic stressors in eastern U.S. national park forests. Forest Ecology and Management. [accessed 25 Oct 2015]; 327: 31-39 http://www.sciencedirect.com/science/article/pii/S0378112714002722
doi: 10.1016/j.foreco.2014.04.033

Fogel, Robert.14 Nov 2006. Shelf fungi. Fun facts about fungi. [accessed 26 Oct 2015]. http://herbarium.usu.edu/fungi/funfacts/shelffungi.htm

Gilbertson, Robert L. Jan-Feb 1980. Wood-Rotting Fungi of North America. Mycologia. [accessed 26 Oct 2015]; 72 (1): 1-49. http://www.jstor.org/stable/pdf/3759417.pdf? acceptTC=true or http://www.jstor.org/stable/3759417?seq=2#page_scan_tab_contents. doi: 10.2307/3759417

Houston D and O’Brien J. 1983. Beech Bark Disease. U.S. Department of Agriculture Forest Service. (Forest Insect and Disease Leaflet 75); [accessed 26 Oct 2015]. http:// http://www.na.fs.fed.us/spfo/pubs/fidls/beechbark/fidl-beech.htm

McKnight, Kent H. and McKnight, Vera B. 1987. Mushrooms. Roger Tory Peterson. Boston: Houghton Mifflin Company.

Roberts, Peter and Evans, Shelley. 2011. The Book of Fungi. The University of Chicago Press. London: Ivy Press.

Ross, D. R. Conks/Shelf Fungi. State of Alaska: Department of Natural Resources. n.d. [accessed 26 Oct 2015]. plants.alaska.gov/pdf/Conks.pdf



11 comments on “Shelf Fungus Diversity and Tree Health at the Morgan Arboretum

  1. Thanks for the post – shelf fungi are truly fascinating, and a have a lot of great natural history to discover and enjoy! Although your work focused on deciduous trees, I wonder if you can comment or speculate on how the results might differ if you looked at coniferous trees. What is known about the comparison between the shelf fungi of deciduous compared to coniferous trees?

  2. Shelf fungi will develop on any fallen logs, stumps, dead branches and standing living trees (Roberts and Evans, 2011)
    However, some polypores only thrive on certain tree species, while others show no preference for the type of wood on which they grow. For example, Lenzites sepiaria only grows on coniferous trees, whereas Lenzites betulina is most often found on deciduous trees. (Underwood, 1902). Therefore, we suppose that the diversity of shelf fungi on coniferous trees will have a similar species pool with the exception of fungi that are host specific.

    Underwood, LM. 1902. The Bracket Fungi. Torreya. 2(6); 87-90. http://www.jstor.org/stable/40594079
    Roberts, Peter and Evans, Shelley. 2011. The Book of Fungi. The University of Chicago Press. London: Ivy Press.

  3. Really enjoyed this post! The Morgan Arboretum provides such a great opportunity to observe and study the beautiful diversity of shelf fungi, and fungi in general. did you come across any Fomes fomentarius? Typically on birch and beech, it has a fascinating history of use for tinder – the 5,000 year old “ice man” discovered in the alps had these mushrooms with him, likely for this purpose. Great section on the effects of shelf fungi on trees! I think there are a few Schizophyllum commune mushrooms in your first picture – are they considered parasitic or opportunistic?

    • Yes, we did come across Fomes fomentarius on some beech trees, and very interesting history! The functions of fungi are so varied, we are learning new ones everyday!
      Schizophyllum commune can cause diseases in humans, so it would be considered opportunistic.
      Kern, M. E., & Uecker, F. A. (1986). Maxillary sinus infection caused by the homobasidiomycetous fungus Schizophyllum commune. Journal of clinical microbiology, 23(6), 1001-1005.

  4. Thank you for sharing this interesting research. It’s unfortunate to note the effect of these fungi on the health of maple trees. I wonder if this could have detrimental effects on the maple tree population of our region in the long run, would there be any way to prevent this?
    Thank you

    • Hi Nathalie!
      Thank you for reading our post and taking the time to provide feedback on it.
      Bark is the tree’s first line of defense against pathogens; if it is breached, the tree is rendered vulnerable, and there is no treatment for wood that has started to decay. Therefore, the most efficient way to protect trees is to prevent wounds. A significant amount of damage to trees is inflicted by human activities (construction, logging, etc.) and could be easily avoided (Gauthier & all. 2015). Certain environmental stressors (abiotic and biotic) may also be limited by caring for trees growing in urban areas.
      The best way to limit large-scale propagation of fungal infestations is through the removal of infected specimens.

      Gauthier NW, Fountain WE & Missun T. 2015. Tree Wounds-Invitations to Wood Decay Fungi. University of Kentucky college of Agriculture, Food and Environment.

      Burns RM & Honkala BH, tech coords. 1990. Silvics of North America: Volume 2, Hardwoods. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service. Washington, DC. 2; 877.

  5. Keep up the great work! You’re absolutely right on the difficulty of correctly IDing fungi. Many angles and knowledge of the substrate are key. For instance, with the hen-of-the-woods (Grifola frondosa), they typically grow near the base of trees and have grey tops, and thin fronds – kind of like a thick, leathery tortilla. So I think the photo above depicts some other polypore. Keep at it and you continue to improve! Identification of fungi is a lifelong endeavour!

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