More than half of the US’s New Hampshire state’s dec-iduous and mixed forest land is dominated by maple, birch, and beech trees, which not only define the picturesque scenery but contribute to the economic resiliency of its communities and help sustain many wildlife species.
But similar to billions of trees in eastern North American forests that have been killed by diseases and insects, beech bark disease has continued to ravage the iconic American beech tree for more than a century.
“Beech bark disease negatively impacts forest health resulting in decreased economic, ecological, and aesthetic value,” said Jeff Garnas, associate professor of forest ecosystem health at the University of New Hampshire (UNH).
“In addition to the loss of many larger beech trees, beech bark disease causes dramatic shifts toward smaller, denser forests over time.”
Among the major mysteries about beech bark disease is how fungi and insects interact with host trees and with one another to cause the disease.
Using genetic sequencing and statistical modelling, researchers are closer to understanding these key interactions which determine the character and severity of the disease.
What makes beech bark disease particularly difficult to study is its manifestation through a “disease complex,” so termed because the disease emerges via the interaction of both an insect – the felted beech scale responsible for producing the white fuzz apparent on many beech trees – and at least two species of pathogenic fungi that cause localised wounds (or cankers) on the trunks.
Since contributing disease agents interact with host trees, the environment, and each other in distinctive ways, the resulting feedbacks are extremely hard to predict and understand.
To gain insights, the researchers – led by postdoctoral scientist Eric Morrison – used DNA sequencing to produce an exhaustive list of fungi in the inner bark of more than 100 beech trees across 10 forested sites from eight eastern states.
The UNH-led team found the early arriving beech bark disease pathogen Neonectria ditissima – a broad generalist that causes canker disease on many broadleaf hosts – is present in more than 42 per cent of infected beech trees sampled.
This discovery refutes the long-standing idea that this fungus is replaced by another, more dominant N. faginata. Rather, they found the two fungi regularly occur together on trees.
“This leads us to hypothesize a much more important role for this fungus including potential interactions with N. faginata and suggests that spillover of the generalist N. ditissima to and from non-beech tree hosts might be an important aspect of disease epidemiology,” said Prof Garnas.
“Given beech’s dominance through much of its range, this demographic shift from larger to smaller beech trees results in major reductions
in carbon storage capacity, nut
crop production, and the availability of cavity nesting habitat, and generally alters the look and feel of the forest.”