Alien species are animals, plants or other species that do not originally belong to a certain location. They have arrived there by human interference. In a globalised world species travel with humans in planes, cars, or ships. They may also arrive somewhere on purpose, through trade in species followed by – accidental or deliberate – release in the wild. Most of these species are harmless and easily fit in with existing biodiversity.

Some alien species, however, find in their new environment perfect conditions to spread quickly and massively. This may cause problems to economy, for example if aquatic plant species such as Floating pennywort block waterways. Or to society, for instance if new species carry disease or are allergenic, such as Common ragweed. They may also harm biodiversity, if species occupy space and compete for resources or simply eat native species, ultimately pushing them to local extinction, which for example Black rats do on small islands. These species are called invasive alien species, or in short IAS.

The impact of IAS on biodiversity has in recent decades become one of the main causes of biodiversity decline worldwide. This is why policies are developed to try and stop IAS from arriving or spreading. Also the European Union has developed such policy by adopting in 2014 the EU Regulation on IAS. This Regulation aims to prevent, minimize and mitigate adverse impacts on biodiversity from IAS across the EU territory.

As part of this policy the most damaging IAS are included in ‘the Union List’, a list of species for which EU member states have particular responsibility to help reach the Regulation’s objectives. These member states also report on their actions and effectiveness, which happened for the first time in 2019.

In support of this Regulation and the reporting process, the European Environment Agency, together with the European Commission Directorate General for the Environment, tasked an international project team to assess the effectiveness of the Regulation, based on the information that is provided through the member state reporting. The study informs about progress in reaching the EU biodiversity strategy’s target to control and eradicate priority IAS.

I was part of the team, led by Wageningen Environmental Research, and developed an assessment framework for the IAS Regulation and recommended ways to present the outcome of such assessment (for example through indicators).