A type of cherry tree originally brought to Belgium with the goal of improving forest health has turned into an environmental problem. The Prunus serotina, also known as the black cherry, was introduced as early as 1930 by Belgian foresters. It was chosen for its fast growth and potential use in timber production. However, over time, it has spread across about a third of the forested areas in Flanders, creating unexpected ecological challenges. One of the main issues with the Prunus serotina is its ability to release chemicals called cyanogenic compounds. These substances make the soil around the cherry trees unsuitable for the germination of native species like acorns and beech nuts. This process, known as allelopathy, results in patches of soil where oak and beech trees—key components of Belgian forests—can no longer grow naturally. As a result, these areas are now dominated by cherry trees instead of the native species. Removing the invasive cherry trees has proven to be both expensive and difficult. Methods such as cutting them down, stripping the bark, or using herbicides have not stopped the trees from regrowing, thanks to their extensive root systems and prolific seed production. The lack of natural predators in Europe has also allowed the species to spread unchecked. The impact of the Prunus serotina goes beyond the forest itself. Oak and beech trees support a wide range of wildlife, including insects, fungi, and birds. Their decline due to the invasive cherry tree has led to a noticeable drop in biodiversity in affected regions. This situation highlights how even well-intentioned introductions of non-native species can lead to unintended and harmful consequences for local ecosystems.