Black locust, Douglas fir and red oak were introduced to Europe several hundred years ago and are among the 530 non-native tree species in Europe. Most of these non-native tree species grow in cities and have also been promoted in forests: some yield higher returns, have more stable root systems or are a particularly striking aesthetic feature. However, they also partially threaten native biodiversity and the associated ecosystem services. As part of the international ALPTREES project, a risk assessment system was developed and handbooks on the management of non-native tree species in forests and urban areas were published.
Compared to urban areas, where non-native trees predominate, the number of non-native trees in forests in the Alpine region is relatively small. According to estimates, European forests consist of approximately 4% non-native trees on average. Of these, only around 5% (i.e. 0.2% in total) are invasive, meaning that if they become established and spread, they pose a risk to native biodiversity.
Risk assessment by location: Given the impacts of climate change on forests and urban areas, non-native tree species will become increasingly important, as they may be better adapted to future climatic conditions. "In ecosystems as critical and sensitive as the Alpine region, potential risks and benefits need to be weighed up particularly carefully before decisions are made", says Katharina Lapin from the Federal Research Centre for Forests (BFW). This is because climate change is also altering the characteristics of already established non-native tree species in such a way that some of them have only become more competitive and invasive under the new changed climatic conditions, particularly in places where native tree species can no longer thrive optimally in their natural forest habitats due to climate change.
Step-by-step guidance: The ALPTREES team, consisting of the project lead BFW and eleven partners, has therefore developed a method for site-specific risk assessment. Stakeholders from forestry, nature conservation, and spatial and urban planning can use a step-by-step guide to distinguish between the negative and positive impacts of non-native tree species on ecosystem services. The guide serves as a decision-making tool for selecting sites, non-native tree species and silvicultural measures in order to limit the associated risks. In general, integrating non-native tree species into mixed forest stands with native species is most straightforward when the ecological characteristics of the introduced non-native tree species are similar to those of native species and the non-native tree species do not display strong dominance behaviour.
Further information about the ALPTREES project can be found here! ALPTREES also offers an Open Knowledge Hub and online course. You can also read about the project "Climate change adaptation in forest management: opportunities and risks of non-native tree species".
