Cherry laurel (Prunus laurocerasus) is native to south-eastern Europe and the Middle East. In Germany cherry laurel became quite popular as an ornamental plant for hedges and is thus planted in many gardens. But for some years now, cherry laurel has also been found as wild growth in German forests and could potentially become a problem. At first glance, a new plant in the forest may not seem too dramatic. But the impact of alien species on local biodiversity can be versatile. For example, introduced species compete with native for sunlight and soil nutrients. In order to investigate the influence of cherry laurel in German forests, PD Dr Stefan Abrahamczyk, botanist at the Natural History Museum Stuttgart, conducted a representative study in the Kottenforst near Bonn together with scientists from the University of Bonn. The study investigated how many cherry laurel plants occur in certain forest areas, the size and age of the plants and whether the plants already bear flowers or fruit.
Indeed, the researchers were able to find many cherry laurel plants in the Kottenforst, in one area almost 50 m2 where covered seamlessly. The oldest found plant was already 30 years old, while many of the other plants found were much younger. Some plants already had flowering and fruiting shoots, which indicates that the cherry laurel is potentially already spreading independently in the forest. The results of the study show that cherry laurel can be classified as a neophyte in Germany. A neophyte is a plant species which is not native to a habitat but got introduced by humans in recent history. As soon as the introduced species has a damaging effect on its new ecosystem, it is referred to as an invasive species. Cherry laurel has a few properties, which could potentially become a problem for other forest plants. Its foliage is for example very dense, making it difficult for light to reach herbaceous plants on the forest floor. It has also been shown that cherry laurel can have an effect on the composition of the soil: The soil becomes drier, the pH-value becomes more acidic, and the availability of important plant nutrients, such as phosphorus, is reduced. And cherry laurel has another competitive advantage. Due to toxic leaf substances, they are less attractive to herbivores, which might make them prefer native species.
In Switzerland, cherry laurel has already been classified as an invasive species and may no longer be traded for cultivation in gardens starting September 2024. It is still unclear whether cherry laurel is already having a negative impact on native species in German forests and can therefore be classified as invasive in Germany as well. To figure this out, follow-up studies are already being planned by Dr Abrahamczyk and his colleagues.