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Beech Bark Disease

The American Beech Tree

The American Beech, by its scientific name Fagus grandifolia, is a deciduous tree native from Nova Scotia. F. grandifolia holds an important role in forestry since its nuts constitute an element of the diet of several species, including humans. Furthermore, due to its hard, heavy and strong wood, Beech trees are a material of choice. Therefore, it also has an economic importance (Tubbs & Houston, 2001)

Beech that shows nuts and leaves

Beech that shows nuts and leaves (Image sources: here  and here)

The Disease

In 1849 a severe disease affecting the American Beech appeared in Europe named Beech bark disease (BBD). Around 1890 BBD was accidentally introduced in Nova Scotia, spreading over most of the North America. BBD, which is now a big threat to North American forests, is the result of an interaction between an insect and a fungus.

The beech scale insects can be recognized by the white wax that they produce for protection, which appear as small white points. They live on Beech bark and feed with their stylet which penetrate the bark and give them access to the sap, creating billions of tiny holes. These holes then stay open due to a substance produced by the scales.

bark with scales

bark with scales (Image source: here)

This large amount of tiny holes constitutes a good environment for the fungi to live, which arrive on the bark as spores transported by wind or rain. The fungi could be Neonectria faginata or Neonectria ditissima, both easily recognizable by their small rounded shape and red color. They attack the bark by creating lemon shaped cankers (around two centimeters in diameter) in each infested wound.

Beech with fungi

Beech with fungi

The disease weakens the wood which leads to difficulties in water circulations and it makes the trunk more likely to break by wind pressure (Lavallé & Laflamme, 2010). Thus, a Beech with a severe infection could present a lower amount of smaller leaves and a large number of cankers infested with little red bubbles on its bark. In most cases, BBD leads to tree death.

Edge Effect

Edge effect can be described as the change in ecosystem structure occurring at the boundary between two habitats. The most pronounced edge effects in forests such as the Morgan Arboretum are caused by trails. They fragment the ecosystem in several sections and can ultimately change it by altering several different factors such as soil, wildlife and plants (Ballantyne, 2014). These factors are impacted not only by the trails themselves but also the increased human traffic. Some commonly researched problems are the introduction of foreign species in these new habitats (Indiana University, 2011) and compaction and erosion of the soil by increased human activity in the forest (e.g. joggers, domestic animals or cars). Other problems include these same activities interfering with the natural habitat of flora and fauna. Included in this, trail networks with high human usage can increase the spread insects and spores through physical and wind dispersal. These are all relevant when looking at the edge effect at the Morgan Arboretum.

These factors could all potentially contribute to changing the surrounding forest. Knowing that trails can cause such edge effects, we wished to study how trails affected BBD and more specifically, if BBD was most severe along trails.

Tree Diversity

The other factor considered in our research question is the influence of tree diversity on the severity of BBD. Tree diversity is influenced by both the number of different species present and the number of trees growing of each species. A forest or tree stand (an area sharing common borders, age and tree diversity) is considered to be Beech dominant if it is composed of around 50% Beech trees or more (McCullough et al., 2005). Previous studies have shown that the age and density of the stand, as well as the tree sizes and the diversity of tree species composing it will have an effect on the severity of the disease. Tree mortality worsens in older stands with numerous mature beech trees. (Houston, 1998).

Having trees of other species surrounding these beech trees can serve them as a buffer against stressors (Grondin & DesRochers, 2013). When managing a stand, either threatened by the incoming of the beech scale or already affected by it, specialists recommend increasing tree diversity which may help in reducing the spread and reproduction of the scale insect. (McCullough et al., 2005). Also, reducing the number of older large beech trees will “lessen the impact of the disease once it reaches the stand” (Grondin & DesRochers, 2013).

Tree diversity has been found to buffer the spread of BBD in highly diverse forests. To assess whether this was applicable in the Arboretum and, if so, how edge effects from trails could alter this buffer, we chose to sample in forest stands with different levels of diversity.

Research Question

What is the impact of edge effects produced by Arboretum trails on the distribution of BBD by comparison of three different forest stands: Beech, Beech/Red Maple and Hemlock/Beech/Red Maple?

Research Methods

In order to assess the impact of edge effect on the distribution of BBD, we chose three forest types to study based on their increasing amount of diversity: Beech, Beech/Red Maple and Hemlock/Beech/Maple. This allowed us to assess any correlation between edge effect and diversity (i.e. if diversity lessens the spread of BBD). Within each forest type, we sampled beech within quadrats measuring 10mx10m along transects at a 90 degree angle from the trail. Quadrats within transects were 20m apart, the first quadrat located trailside. In addition, transects were separated by 10m to cover more forest area and make sure no trees were counted twice. Overall, 9 quadrats were sampled in each area. For every Beech tree we measured diameter at breast height (DBH) in centimeters, and the severity of: scales, cankers, fungi, and bark loss. The severity of each characteristic was rated on a scale of 0 to 2, 0 being absent/non=severe and 2 being present/severe. From this, a total score was calculated for each tree indicating BBD severity on a scale of 0-8. In this way, each quadrat could be analyzed for its average BBD severity. This allows us to more accurately depict whether or not the edge effects from the trail are positively affecting distribution of the BBD (i.e. helping to spread the disease).

Group pictures

Group pictures

References

Ballantyne, M., Gudes, O. & Pickering, C. M. (2014). Recreational trails are an important cause of fragmentation in endangered urban forests: A case-study from Australia. Science Direct, 130, 112-124. Retrieved from http://www.sciencedirect.com/science/article/pii/S0169204614001595 Date accessed 05/11/14

Fernald & Rehder. (1997). Flora of North America. Volume 3. Page 1788.

Lavallé, R. & Laflamme, G. (2010). Le hêtre menacé par une maladie redoutable en Amérique. Progrès forestier. Printemps 2010. Page 31-33.

Predicting Invasive Species Spread: Spread of Invasive Species (2011). Retrieved from http://www.indiana.edu/~preserve/InvasiveSpread/. Date accessed: 05/11/14.

Tubbs, C.H. & Houston, D.R. (2001). Silvics of North America. Volume 2: Hardwoods. Page 330.

Weaver T. & Dale D. (1978). Trampling Effects of Hikers, Motorcycles and Horses in Meadows and Forests. Journal of Applied Ecology, Vol. 15 no. 2, 451-457. Retrieved from http://www.jstor.org/stable/2402604?seq=5. Date accessed: 05/11/14.

Grondin, J., and DesRochers, P. “Beech Bark Disease.” Natural Resources Canada. Government of Canada, 11 Dec 2013. Web. 5 Nov 2014

Houston, D.R. “Beech Bark Disease” North Central Research Station, USDA Forest Service, 1998. Web. 5 Nov 2014

McCullough, Deborah G., and Heyd, Robert L., and O’Brien, Joseph G. “Biology and Management of Beech Bark Disease.” Michigan State University Extension, Extension Bulletin E-2746. (Reprinted 2005): Page 7. Print.

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About Crystal Ernst

Hakai Institute postdoctoral scholar at Simon Fraser University (B.C.)

15 comments on “Beech Bark Disease

  1. Nice post! It’s a good overview of beech bark disease. I do like the connection to trail networks at the arboretum.

    How do you think climate change will affect the distribution of the disease into the future? I seem to recall reading about cold winter temperatures as being critical to stopping the spread further north. What are your thoughts on this? Will we eventually see the disease across the entire range of beech in North America?

    • Beech Bark Disease seems to be a losing battle. There is no way to stop the disease from spreading and it will therefore continue to spread across the continent. According to the mortality section in the following article (http://www.baycounty-mi.gov/Docs/Health/GypsyMoth/BeechBark.pdf) most of the scale insects won’t survive after a few days of very cold weather, but they have the ability to take shelter in the tree protected by moss. As of right now, it would be difficult for these insects to invade trees father north because only a few could survive the winter.

      As the northern climate changes, North American biomes are experiencing warming, which would expand the range of scale insects and other pathogens affecting Beech trees. An excellent article attempting to explain how climate change could affect forests in North America in terms of pathogens and herbivores can be be found at the following URL (link)
      http://www.baycounty-mi.gov

  2. Beech Bark Disease seems to be a losing battle. There is no way to stop the disease from spreading and it will therefore continue to spread across the continent. According to the mortality section in the following article (http://www.baycounty-mi.gov/Docs/Health/GypsyMoth/BeechBark.pdf) most of the scale insects won’t survive after a few days of very cold weather, but they have the ability to take shelter in the tree protected by moss. As of right now, it would be difficult for these insects to invade trees father north because only a few could survive the winter.

    As the northern climate changes, North American biomes are experiencing warming, which would expand the range of scale insects and other pathogens affecting Beech trees. An excellent article attempting to explain how climate change could affect forests in North America in terms of pathogens and herbivores can be be found at the following URL (http://www.dartmouth.edu/~mpayres/pubs/gepidem.PDF). We believe that, with current warming predictions, the disease will expand its range in more northern regions of North America, quite possibly throughout the entire range of beech (though this may take a few decades).

  3. I’m curious, have you starting to see a trend in your results? Does the edge affect play a major role?

  4. Very informative post! I would be curious to know as to how the disease was first accidentally introduced in Nova Scotia?

  5. Very interesting! Do you know if it will lead to the extinction of the americain beech? And do you know at which rate the disease is spreading?

    • Thank you for the feedback and questions Andrea!

      Many specialists do believe that Beech Bark Disease will lead to the extinction of the American Beech tree. According to the following article (http://www.lapresse.ca/
      maison/cour-et-jardin/200604/18/01-868940-adieu-pesticides.php), one professor from University of Montreal believes their extinction could be as soon as 25 years from now. He states that in certain areas of New-England, 80-90% of the population has already died.

      As for the rate of spreading, according to the following study, http://www.sandylie
      bhold.com/pubs/Morin_etal_CJFR.pdf, it is 14.7 (+/- 0.9) km/year but this rate is impacted by several factors.

      Hope this helps!

  6. Hi there Kim!
    We are currently in the process of analyzing our data. So far we are able to see some trends in the Beech dominant forest just by looking at the raw data, but further analysis is underway to truly assess whether our observations are just!

    Hope this answers your question! We’ll keep you posted.

    Thanks for asking.

  7. Informative and clear. I would be interested in knowing if there was any government funded research on BBD.

    • Hi there Jane,
      We’re sorry for the late reply, but rest assured; we haven’t forgotten you!

      Lots of research has been conducted over the years on Beech Bark Disease, many linked to provincial and federal organizations in Canada such as “Ontario Invasive Species” and even “Environment Canada”. As their websites indicate, this research was most probably a collection of previously obtained data which they projected on their sites for public awareness and policy. Research conducted by a multitude of organizations often depend on some form funding from the government, be it a small or large amount. An example of this would be research grants for grad students who are researching Beech Bark Disease. We found a large amount of information on the disease via USDA Forest Service, which is also linked to the government (USA).

      The link below explains how science funding works in the United-States. Though Canada may be a little bit different, we found it could be helpful:
      http://undsci.berkeley.edu/article/0_0_0/who_pays

      Here is a link to one of the larger players in Canadian science funding – NSERC:
      http://www.nserc-crsng.gc.ca/index_eng.asp

      We hope this helps!

  8. Very Interesting! What tool did you use to extract the 10cmx10cm samples of bark?

    • Hi Diad!

      I think you might have misunderstood our methods. We didn’t cut into any trees.
      In fact, we measured out 10x10meter quadrats (a square sample area in the forest) where we assessed the severity of each beech tree in the quadrat by visually examining the presence of scale insects, cankers, fungi, and bark loss.

      We can assure you that no trees were harmed during our research!

  9. I stumbled on this while researching Ash borer gains in the West Island, very interesting.
    Thank you!

  10. Keep up the fantastic piece of work, I read few blog posts on this internet site and I believe that your site is rattling interesting and has got sets of great info .

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