Invasive plants in the EU Part 3: Grasses

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. In this series’ previous articles, we have presented shrubs and trees and aquatic plants; today we are looking at grasses. Make sure to also check out our articles about invasive vines, perennial and annual herbaceous plants.

Andropogon virginicus, the blue-stemmed sedge

Seeds of the American bluegrass (Andropogon virginicus) were probably brought to Europe via horticultural seed mixtures, contaminated machinery, clothing and hay imports, and contaminated NATO munitions on a military training area in France probably led to its introduction there.
The plant forms persistent tufts that can grow to over 2 meters tall and contain large amounts of dead material, which is considered to be fire-inducing. They quickly develop a dense growth that takes away the space for existing species to develop. In addition, when they decompose, certain chemical substances are released that reduce the fertility of the surrounding soil.

Cortaderia jubata, the purple pampas grass

Pampas grasses are popular ornamental plants, but not all members of this genus have invasive tendencies. In addition, it is difficult to determine the exact species – some taxonomists assume that Cortaderia jubata is only a subspecies of Cortaderia selloana, which also tends to run wild. The seeds need open, sunny and moist conditions to germinate, which makes them particularly problematic in coastal regions and dune landscapes. Even though there are currently only a few places in Europe where Cortaderia jubata is established, model calculations assume that there is a considerable risk of invasion for large parts of southern and western Europe as a result of climate change.

Ehrharta calycina, the steppe grass

Ehrharta calycina, a grass native to Africa, is already established in Portugal and Spain. As its seeds are spread by the wind and germinate easily in open areas, there is also a risk that this species will successfully spread to other parts of Europe. Once established, it transforms diverse habitats such as dunes and bushes into grasslands that pose a major fire hazard. After a fire, it quickly sprouts again and thus successfully suppresses other species. Ehrharta calycina also has allelopathic properties: Its presence leads to a shift in the nutrient cycle by accumulating phosphorus from the biomass in the soil.

Microstegium vimineum, the Japanese stilt grass

Microstegium vimineum has already been documented to spread by various means: The adhesion of the seeds or fruit to travelers’ clothing and shoes, contaminated birdseed, equipment and vehicles used in agriculture, forestry, construction or waste disposal. So far, the species has been detected in Turkey, Georgia and the North Caucasus, along roads and railroads, ditches and forest roads, in riparian forests, wet meadows, commercial forests, along forest and river edges. Its numerous creeping shoots displace weaker species and shade the ground. This results in a variety of changes to the soil properties and the composition of the resident herbivore and arthropod communities.

Cenchrus setaceus, the African lamp grass

Once prized as an ornamental plant, Cenchrus setaceus is now spreading in Spain (Balearic and Canary Islands), France, Italy (Calabria, Sardinia, Sicily), the Portuguese Algarve, Cyprus and Malta. Climate change is making other regions of Europe attractive for colonization, especially dry and stony grasslands and coastal landscapes. As the species draws the remaining water from the soil and alters the nutrient cycle, its presence has a negative impact on local biodiversity.

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: steppe grass (Ehrharta calycina plant6) by Harry Rose, CC BY  2.0 via flickr.