Invasive alien species: what the IPBES report says

In September 2023 the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) published a significant report on invasive alien species entitled ‘Assessment Report on Invasive Alien Species and their Control’.

It results from four years of analysis conducted by a multidisciplinary team of 86 scientists from 49 countries, supported by 200 collaborators. It is the first synthesis report that brings together the best scientific knowledge on invasive alien species internationally.

Alien species (also known as allochthonous or exotic) refers to species introduced – voluntarily or involuntarily – into new areas through human activities.

It is important to emphasize that not all alien species are invasive. Invasive alien species are, in fact, a subcategory of alien species: they are animals, plants and other organisms that have established themselves and spread, causing negative impacts on biodiversity, local ecosystems and native species.

Human activities have introduced 37,000 alien species into different regions and biomes of the world at a rate of about 200 each year. Of these, more than 3,500 threaten biodiversity, the economy, ecosystem services, health and people’s quality of life. 1,061 are exotic plants, 1,852 exotic invertebrates, 461 exotic vertebrates and 141 exotic microbes.

Most impacts were reported in the Americas (34%), Europe and Central Asia (31%) and Asia-Pacific (25%), with fewer reports in Africa (7%).

The impact of biological invasions on the global economy in 2019 was USD 423 billion. IPBES states that economic costs have quadrupled every ten years since 1970.

According to the 2019 IPBES Global Assessment Report, invasive alien species are one of the top five causes of biodiversity loss, along with land and sea use change, direct exploitation of natural resources, the climate crisis, and chemical and waste pollution. 

The IPBES report states that invasive species have contributed to the extinction of 60% of terrestrial plants and animals, while they have directly caused the extinction of 16%. Another figure highlights the impact on biodiversity: 218 invasive alien species have caused the extinction of more than 1,200 native species. 

The Castor canadensis (North American beaver) and the Magallana gigas (oyster spread along the Asian Pacific coast), for example, change ecosystem properties by transforming habitats, with cascading effects on a myriad of native species.

Biodiversity loss also initiates a vicious cycle that encourages the introduction and spread of other invasive alien species. As these species spread, ecosystems will be less diverse and less resilient and thus less able to absorb the entry of future alien species.

The negative impacts on people concentrate on those living in more direct contact with nature, such as indigenous peoples and local communities, affecting the economy, food security, quality of life and health. 

Some invasive mosquito species, for example, can act as vectors of infectious diseases and lead to epidemics such as malaria, dengue fever, chikungunya, Zika, yellow fever and West Nile fever.

In many cases, invasive alien species negatively affect the ecosystem services that nature provides for people. 

In New England and Canada, Carcinus maenas (common crab) has impacted commercial shellfish beds; along the Korean coast, Asterias amurensis (Pacific starfish) and Ciona intestinalis (long ascidian) have negatively impacted mariculture and fisheries; in India, Mytilopsis sallei (a mussel-like mollusc) has supplanted native clams and oysters, essential resources for local fishing .

In addition to the contents of the report, it is helpful to take a slight diversion concerning our country, given the resonance that the topic of alien species has gained in 2023. In Italy, the case of the Callinectes sapidus (better known as the ‘blue crab’) is well known: a precise example of the impact on ecosystem services and the local economy. 

This species is native to the western coasts of the American continent and has spread to the Mediterranean, transported by ships’ ballast water. Blue crabs destroy shellfish farms, cut fishing nets with their claws and feed on the fries (the young fish), damaging fisheries and fish stocks. 

On the other hand, an example from the plant world is robinia pseudoacacia, a tree native to North America from which acacia honey is made. It is considered an invasive species, as it tends to replace poplars and willows along river banks.

Three basic approaches emerge from the IPBES report to deal with threats from invasive alien species: prevention, containment and eradication.

Prevention is the most effective (including cost-effective) measure in the fight against biological invasions. The introduction of new alien species into new habitats can be prevented through stringent measures, such as well-enforced import controls, biosecurity and strategies to prevent escape from confinement. This approach is essential in marine systems, where eradication and containment attempts often fail.

Containment is a viable option when eradication is unfeasible. This approach focuses on limiting the spread of invasive alien species and keeping their populations within manageable limits. However, containment is most effective in terrestrial and enclosed water systems, less so in marine systems.

Eradication can be successfully adopted for small and slowly spreading populations of invasive alien species. This approach has demonstrated significant success, especially on many islands.

In this scenario, it is essential to take concrete actions to protect biodiversity, considering the crucial role it plays in the ecological balance of our planet. Etifor has been working with forest managers and local administrations for years to implement environmental projects. One example is our work in promoting sustainable forest management practices, which contribute not only to conserving biodiversity but also to mitigating the effects of the climate crisis and promoting responsible management of natural resources.

One example is the BioClima initiative, implemented by the Lombardy Region – through the funds of the Lombardy Plan – and with the support of the Cariplo Foundation. BioClima aims to create public-private financing models to catalyse investments in biodiversity conservation and climate change adaptation projects in Lombardy’s forests and protected areas, thus helping to save 12 ecosystems and 70 wildlife species.