There are species in the urban fauna and flora that actually decrease biodiversity. Increasing biodiversity in cities comes with managing those species and prevent them from settling. They are referred to as invasive alien species (IAS): “species whose introduction and/or spread outside their natural past or present distribution threatens biological diversity”. They are considered to be the second most important cause of biodiversity loss, after habitat loss and fragmentation. The number of IAS in Europe has increased steadily over the last 100 years. Many non-native species have been introduced intentionally. They include trees and crops from other continents that are more productive, ornamental plants for gardens and pets. Other species have arrived accidentally, thanks to growing international trade and travel, as ‘stowaways’ trapped in freight containers or “contaminants” – for instance, mussels carried on the hulls of ships. Although the majority of non-native species cause no harm, some spread very rapidly and can harm biological diversity, human health, and/or economic and aesthetic values.

According to the DAISIE project there are more than 12000 non-native species in Europe. DAISIE also showed that biological invasions can disrupt the services provided by ecosystems, with significant socio-economic consequences. IAS can, for instance, alter ecosystem processes, reduce biodiversity, change landscapes and reduce the value of land and water for human activities. In 2012 the EEA3 identified 14 types of IAS impacts in Europe at four different levels: biodiversity, ecosystem services, human health, and economic activities. Negative impact on ecosystem services, human health resulting in high costs.

Read more about invasive species in the new brochure on invasive species published by the European LIFE project.