When Invasive Species and Climate change join forces
Emerging infectious diseases threaten human health, agriculture and biodiversity. The occurrence of emerging diseases in forest ecosystems has exponentially increased over the last four decades in Europe. The most common drivers of new forest disease emergence are the introduction of exotic pathogens in new geographic areas and climate change.
One example of forest disease linked to climate extremes that is increasing in Europe is the Sooty Bark Disease (SBD) in sycamore maple (Acer pseudoplatanus) trees. The SBD is caused by the ascomycete fungus Cryptostroma corticale, putatively native to eastern North America, which can also be pathogenic for humans, causing pneumonitis. The SBD was first reported in England in 1945 and, after the year 2000, has been more frequently reported in Europe.
A recent study aimed at analysing the emergence of SBD in Europe through the frequency of spore detection in aerobiological samples and time-series of disease records.
Results show that the SBD on trees is at an exponentially increasing phase in France and Switzerland with an increase in the magnitude of the number of cases that peaks following a marked water deficit. Those episodic disease peaks do not show a deceleration, and may continue to increase as drought events do.
The occurrence rate of SBD confirms that the development of this invasive disease is linked to extreme climatic conditions. Data show that drought favors pathogen development. Outbreaks of the disease are associated with the occurrence of more than 33 days of a temperature higher than 25 °C per year during the two years preceding the disease. The hope is that early aerial detection of C. corticale in disease-free countries could help implement more efficient measures for SBD detection and eradication in the field.
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