Black Cherry Trees Invade Europe

Black Cherry flowers

We have long known that plant and animal species are successful in becoming invasive when they arrive in a new land without their usual predators.  Now there is more evidence to support this theory.
Black Cherry have long been successful in growing in our forests, sometimes to the point that they are sometimes considered a nuisance species.   Like most native species, they have reached a a balance with their neighbors without out-competing them. Our black cherry trees however have become an invasive species in Europe.
Pythium is a fungal pathogen which causes a disease in black cherry trees called damping-off disease.  The disease kills seedlings in fields and greenhouses.
Studies reported in Sciencedaily.com found that Pythium could be found in 20 comparable forests in North America and in Europe.  However, its ability to kill trees was far less in Europe's forest's strain.

"Reinhart and colleagues tested the virulence of each Pythium isolate. They then used DNA sequencing to identify each isolate. They found that some non aggressive Pythium types were common in both ranges, but aggressive types were found only among samples from the tree's native range."

This study suggests that Pythium serves as a natural control in our forests to keep the population in balance.  Human pathogens such as E. coli and influenza virus vary in their virulence or ability to cause disease.  This is evidence of the same mechanisms in plant fungi.