• Matthew McCartin

The End of Beech?

Updated: May 8, 2018

The subject of biodiversity and the changes to our natural world that are happening as a result of human society and connectivity is well beyond the subject of a “Blog”.

We are all not only witness to, but key participants in an experiment with the natural world that has never been conducted before.

What that means to me is that our individual responses to these changes matters greatly, as we all represent individual opportunities to address these novel challenges in novel ways. This universal trend is generated by local realities and it is the local nature of this trend that gives us the power to exert influence with care.

Enter Beech Leaf Disease, or BLD. BLD seems to be the latest in a long list of biological afflictions that has the potential to alter our local arboreal landscape. It is not yet common knowledge and does not enter conversations as readily as Emerald Ash Borer, Asian Long-Horned Beetle, Oak Wilt, Beech Bark Disease, Boxwood Blight, or Hemlock Woolly Adelgid. This is partly because this “disease” is new, but also because unlike the aforementioned issues, BLD has as yet no known cause or cure.

Let’s briefly review its history.

BLD was first discovered by John Pogacnik in 2012, a biologist in Ohio, USA. The disease, which exhibits symptoms mostly on it’s foliage, has since progressed quickly throughout native American Beech stands in Ohio, Pennsylvania, New York and now Ontario. Once it’s potential severity was recognized, other qualified researchers joined in to try and identify the problem, such as professor of plant pathology Enrico Bonello at Ohio State University. While infection is thorough and rapid, tree mortality rates and whether infected trees can recover remains as elusive as the cause. As the disease continues to spread unchecked, it has also become clear that no type of Beech is immune. European and Asian Beech in the Holden Arboretum of Ohio’s collection have proven as susceptible as the native American species.

How does this translate as a local challenge?

As most in the Ontario industry know, Beech species are quite possibly the most versatile landscape trees. From weeping to coloured varieties, as architectural accents to privacy hedging plants, Beech are a major component not only of Toronto’s landscape, but also of the income of those that grow and plant them. It can be said that the use of European Green Beech (Fagus sylvatica) has been used with monoculture-like consistency for the purpose of residential privacy for the past decade in the GTA. As a hedge, European Beech can be grown in sun and shade, can be shaped to requirement indefinitely and has a tan leaf that is retained over winter, giving it an ‘evergreen’ quality. Few trees have such a high landscape value.

What are the stages for addressing the problem?

First, is to educate. Below are links to the main pages of information on BLD that are available online. Nurseries and Arborists should become familiar with its history as well as be able to identify it through the many pictures that have been posted of the known symptoms.

Second, is not to overreact. Research is well underway in the US to attempt to ID the pathogen(s) and hopefully once it’s better understood, there will be ways of managing the disease in our landscapes. A ‘managed’ approach is currently what we do in the case of many other known pathogens, including those mentioned previously. While the plight and future of forest species, American Beech in this case, will have to rely on their plant communities and genetics to survive human-induced disease challenges, science and industry can manage their longevity in our built environments.

Third, is to ensure that the Beech that exist in our landscape and that continue to be planted are as healthy as possible. Ensure that the trees are not undergoing other forms of stress, which will directly affect their ability to adapt to new challenges. Avoid a chemical approach to the problem. A tree that has its microbiome intact and that can use its own immunity and biological resources to respond to stress, has the best chance not only of survival but of helping to indicate what shortcomings biological solutions may have. A tree that is otherwise healthy will not readily mislead an investigator with symptoms that are related to a multitude of other issues.

Lastly, is species selection. European Beech in my opinion should still be a popular choice, but this is a good opportunity to consider some alternatives. The ‘next best thing’ that fulfills our hedging Beech needs is likely European Hornbeam (Carpinus betulus). Hornbeam, unlike Beech, is in the Birch family (Betulaceae) and as such will not fall prey to this species-specific ailment. Hornbeam has many of the same desirable traits as Beech and even surpasses Beech in the beauty of its bark and trunk, its evident love of being pruned and shaped, as well as a slightly hardier constitution. The one trait that has made Beech more popular is that Beech retains its winter leaf with greater consistency. While Hornbeam will also retain a similar leaf, it’s ability to do so is less predictable. Individual trees will exhibit higher leaf retention, but seasonal/biological cues ultimately seem to change what appear to be genetic predilections. This topic of leaf ‘Marcescence’, or dead leaf retention, will be footnoted below and could easily be the subject of future blogs. With the planting of Hornbeam, unlike Beech, care must also be taken to anticipate wood borers, which should be addressed in a timely way following transplanting.

Clearly the subjects of biodiversity and global community continue to infiltrate our lives in unpredictable ways. We should take note that urban plant communities are going to be less able to adapt to stress unless we help foster an ethos of responsibility and health, unless we as educated professionals disseminate intelligent advice. Species diversity, qualified and critical tree selection, responsible and traceable nursery purchases, reputable companies that exhibit expertise and trained staff: these are more than ever the requirements of the professionals that influence client purchases.

These conversations will grow the forests of tomorrow.


** ENDNOTE: Perhaps a subject for a future blog, we at Hylaeus have been studying the biological phenomenon, known as Marcescence (dead leaf retention). We have been exploring the biological stages of leaf abscission and how to achieve leaf Marcescence in other plant species through organic intervention. This approach has a big advantage over the plant-breeding solution. Basically, if plant breeders were able to select special strains of Hornbeam that retained a winter leaf, there’s no telling whether that selected individual that gets replicated in commerce will have the entire Hornbeam genome to face future challenges. If the leaf-retentive tree turns out to be deficient in its genetic resources to overcome unforeseen future challenges, we will have unwittingly made a ‘weak’ version of hornbeam prevalent in our environment. Understanding how to organically encourage Marcescence however, will not only preserve a tree’s entire genomic gifts, but increase our species selections as well. As Hornbeam have an attractive tan leaf in winter, we’ve chosen it as a good place to start.

#toronto #urbanforest #bld #beechleafdisease #trees


An exciting article recently published gives hope for intervention:

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