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Alien tree species may inhibit the setup of animal food chains, compete with native tree species for locations, or change habitats. Moreover, non-indigenous tree species may bring other alien organisms into our country—often to the disadvantage of native species, for such “stowaways” are sometimes not content to infest their original host plants, attacking native species as well. Switzerland’s elm stands, for example, are being devastated by Dutch elm disease, a fungal infection believed to have been imported from Asia. Only a few insect species—mainly those making scarcely specialized demands on their food—are able to benefit from introduced species.
Of the non-indigenous tree species mentioned above, only the Black Locust is causing major problems, albeit above all at forest skirts or entirely outside the forest range. Black Locusts disperse spontaneously, colonizing ruderal areas and non-fertilized meadows. Since they enrich soils with nitrogen, they allow nutrient-loving plants to grow on formerly poor soil. This is the reason why the Black Locust has been blacklisted.
Fortunately enough, however, the E8 indicator shows that cultivating non-indigenous tree species is of almost no importance in Switzerland, and there is no increasing trend emerging, either. |
