Invasive plants in the EU Part 1: Shrubs and trees

Union list of invasive species

There are around 12,000 alien species in the EU. A small number of them require special attention as they can endanger the populations of native species.

The EU regulation on the prevention and management of the introduction and spread of invasive alien species is intended to prevent these species from spreading and to enable a rapid response when the first signs of spread appear. The exact species concerned are listed in the “Union list”. Of the 88 invasive species listed, 40 are vascular plants. Today we are looking at shrubs and trees. In this series you can also find articles about aquatic plants, grasses, vines, perennial and annual herbaceous plants.

Shrubs and small trees

The 2-6 meter tall willow-leaf acacia (Acacia saligna) originates from Australia and reproduces rapidly, allowing dominant stands to form. As it also accumulates nitrogen in the soil, it displaces species that are dependent on nutrient-poor soils. The crossbush (Baccharis halimifolia) tolerates high salt levels in the soil, displaces reeds and rushes and thus alters sensitive habitats such as salt marshes. The needle-leaved pincushion (Hakea sericea) colonises disturbed areas in dense stands, e.g. roadsides, forest edges, dry grassland and pine forests. The common milkweed (Asclepias syriaca) was once introduced to Europe as a bee pasture and is now displacing native plant species on dry grassland sites due to its rapid spread and large populations.

Larger trees

There are still no stable populations of the mesquite tree (Prosopis juliflora) in Europe except on Gran Canaria. It is one of the 100 most invasive woody plants in the world, which is why it was included on the list as a precautionary measure. The Chinese tallow tree (Triadica sebifera) is also under observation. Its potential distribution area is the Mediterranean region, the south-west of the Iberian Peninsula and the southern and eastern parts of the Black Sea coast. The tree of heaven (Ailanthus altissima) is already widespread in large parts of Europe, and climate change is further favoring its spread. A single individual can produce up to 325,000 seeds per year. It also reproduces vegetatively by stolons. Its metabolism inhibits the growth of plants in its neighborhood (allelopathy).

Documenting the spread

If you identify plants with Flora Incognita and allow access to your location, your find will become part of a scientific data collection that enables our scientists to research the distribution of species in time and space. You can read about our research work here. This data can also be used to plan and implement nature conservation management measures quickly and effectively. Thank you for your help!

Attention! The species on the Union list may not be intentionally introduced into the territory of the EU, kept, bred, traded, used, exchanged, used for reproduction or released into the environment!

Featured image: Tree of heaven (Ailanthus altissima 004.JPG) by H. Zell. CC BY-SA 3.0.