[Publication] Exotic tree species in European forests examined by experts

Exotic species that have been purposefully or accidentally introduced (e.g. during air transport) into European forests can highlight environmental and socioeconomic challenges. The interactions of these species with native or indigenous species (originating in the area in question), the risk of biological invasion and the financial cost of their management are all major issues. What impact do they have on biodiversity? How can national or regional management plans be developed when the risk of invasion disregards borders? The book Introduced tree species in European forests: challenges and opportunities was edited by experts and brings together a broad spectrum of case studies and results from the scientific literature with the aim of answering these questions and encouraging a specifically adapted method of forest management. This collection is part of the In-Tree project led by the German Federal Ministry of Food and Agriculture and the European Forest Institute.

Several chapters of the book include research conducted by Irstea.

  • Impact of exotic introduced species on biodiversity

The impact of these species on biodiversity depends on the ecological context involved, explains Yann Dumas, Irstea researcher and author of chapter 4.6. For example, colonization of a ruderalized area, on soil made from rubble, would have a positive impact, while the afforestation of a natural area with high environmental value would have a negative impact on overall biodiversity as it could lead to a reduction in rare species. Therefore, exotic species should be particularly excluded because they risk invading natural areas with high environmental value. According to Dumas, studies are needed on a European scale to evaluate the biodiversity linked to each indigenous tree species in order to estimate the loss of biodiversity that would occur if it were replaced by an exotic species.

  • Impact of the Ailanthus species on the protective effect of forests

Chapter 5.7 was written by 4 researchers from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and focuses on the introduction and spread of the tree of heaven (Ailanthus altissima) in Switzerland. The chapter summarizes the work carried out with Irstea researchers from Irstea's Grenoble Center as part of the ALIEN project. The aim of the study is to evaluate the impact of this invasive species on the protective effect of forests against rockfalls in France and Switzerland.

  • Monitoring invasive knotweeds

In chapter 3.8, Fanny Dommanget, Paul Cavaillé, André Evette and François-Marie Martin, all from Irstea's Grenoble Center, focus on the spread of Asian knotweeds and their competitive interactions with native species in Europe. Methods used to control their invasion (e.g. weed killers, mowing) have been shown to be ineffective and expensive.  Two strategies are recommended: observation and prevention.

The book, aimed at forest management stakeholders, public decision-makers, researchers, students and anyone else interested in the subject, is freely available on this link.

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