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Environment
3rd November 2020 / Issue 551
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Source:Grosdidier, M., Scordia, T., Loos, R. and Marçais, B. (2020) Landscape epidemiology of ash dieback. Journal of Ecology, 108(5): 1789–1799.
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Landscape features of European ash tree populations increase resilience against dieback disease
Ash dieback disease, caused by an invasive fungal pathogen, was introduced into Europe via Poland in the 1990s, and reached France in 2008. The disease causes leaf infections, shoot blight and ‘collar cankers’ — damage at the base of the trunk — eventually killing the tree. A study investigates how landscape features impacted the spread of the disease in north-eastern France, in order to inform future management decisions and efforts to limit its spread.
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Ash dieback is an emerging fungal disease caused by Hymenoscyphus fraxineus and has severely damaged European ash stands since its introduction from Asia. Local conditions such as climate or site conditions are known to affect ash dieback, and it has been suggested that landscape features might also have an impact on the spread of the disease.
Characterising how the surrounding landscape influences disease spread is important in understanding how to reduce its impact. As ash trees are stationary and spatially spread-out hosts, landscape features such as roads and watercourses could act as conduits for spreading ash dieback disease. Moreover, microclimates that increase the chances of the fungus surviving could be influenced by topography — the physical feature of an area of land.
This study conducted a landscape survey of an area affected by ash dieback. The 22-square-kilometre study area was near the village of Champenoux, north-eastern France, and included forest and agricultural settings with scattered hedges and small woods. The survey was repeated at different stages of disease development, either shortly after disease arrival in 2012, or after several years of disease development (2016–2018). The researchers then used a statistical model to analyse the effects of the environment on tree crowns (branches, leaves and reproductive structures), dieback severity, collar canker and the abundance of infected leaves in the leaf litter.
The analysis found that landscape features are less important at the early establishment stages of the disease, but strongly affect how ash dieback develops and spreads through ash populations. The disease was noted to be less severe where ash density was low in forests, and in open canopies featuring hedges or isolated trees. The microclimates in the crowns of these isolated tees were found to be less favourable
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Landscape features of European ash tree populations increase resilience against dieback disease (continued)
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The contents and views included in Science for Environment Policy are based on independent, peer-reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.
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to the survival of ash dieback fungi. Ash trees in Europe are often found in these types of landscapes, so the researchers suggest this should limit the severity of ash dieback.
This study suggests that no further action needs to be taken regarding protecting the European population of ash as the species commonly occurs in open landscapes. However, the results could also inform future forest planning and planting regimes by helping to identify actions that would achieve a preventative effect against the development and spread of such diseases.
