Tuesday, December 12, was all about biodiversity, as Aarhus University hosted a symposium on invasive species based on the new IPBES report. Among the symposium’s keynote speakers, we had the pleasure of welcoming Professor Helen Roy and Associate Professor Alejandro Ordonez Gloria, both of whom played a key role in the report’s development.
The lack of space is one of the main reasons why biodiversity is under pressure, as many people can surely attest. But water hyacinth, the house rat, and black locust also pose a problem in various parts of the world. All three are examples of invasive species that have been collectively identified by IPBES as one of the five greatest threats to biodiversity and ecosystem services.
Invasive species are a contributing factor in 60% of species extinctions globally, and in 16% of documented cases, invasive species are the direct cause of a species’ extinction. The annual economic costs associated with invasive species are estimated at approximately $420 billion per year, and the positive effects that some invasive species may have are far outweighed by the negative effects, which, in addition to extinctions, include the degradation of ecosystem services—such as negative impacts on food production and an increased risk of disease spread.
Symposium at Aarhus University
Until recently, the extent of the challenge posed by invasive species had been underestimated. But in September 2023, the 140 member states of IPBES adopted the latest global consensus report, titled Thematic Assessment Report on Invasive Alien Species and their Control, which is the result of four years of work led by 86 international scientists and experts from 49 countries and a thorough review of more than 13,000 references.
Based on the report’s conclusions, Aarhus University organized the symposium “Invasive Species — From a Global Overview to Local Control,” organized by IPBES in Denmark with a grant from the 15 June Foundation, featuring participants from research communities, municipalities, NGOs, businesses, as well as government agencies and ministries.
Invasive Species: A Global Overview
Among the speakers were Professor Helen Roy from the UK Centre for Ecology & Hydrology and Associate Professor Alejandro Ordonez Gloria from Aarhus University. Both have played a key role in the development of the latest IPBES report on invasive species. Helen Roy served as the lead scientist for the report from 2019 to 2023, and opened the international portion of the program by outlining the report’s key messages, including that a total of 3,500 species have been identified as invasive, with negative impacts on other species—including humans—and our natural resources.
See also: New report highlights one of the driving forces behind the biodiversity crisis
Helen Roy also noted that the threat posed by invasive species is increasing in all regions of the world, that the spread of invasive species is, by definition, caused by humans, and that we are therefore also a crucial part of the solution. Three key management measures are to stop the spread and establishment of invasive species through their pathways of dispersal, taking strong action against selected invasive species and targeting control efforts at specific locations—such as islands—where successful eradication is possible and has, in fact, been achieved in many cases. Restoring the integrity of ecosystems can also counteract the effects of invasive species.
Alejandro Ordonez Gloria, who served as lead author of the report’s chapter on governance, went on to describe why it is so difficult to prevent the spread of and combat invasive species. Although the task is complex, a key conclusion is that the challenge—including the economic consequences—will only grow: “The cost of inaction.” Therefore, it is crucial to take action early and effectively. Once invasive species have become established, it is often impossible to combat them effectively; the only option is to manage populations and mitigate the effects.
The subsequent presentation by Peter Stæhr, a professor at Aarhus University, on invasive species in the marine environment—with a focus on Danish waters—only served to confirm that the task of combating invasive species, once they have become established, is, in almost all cases, impossible in the ocean, thereby underscoring the need for monitoring to prevent further spread. In the subsequent panel discussion, Helen Roy emphasized the importance of comprehensive communication about the many negative effects of invasive species at all levels.
Biodiversity Act, goby, and oysters
Later in the symposium program, the focus shifted to national and more practice-oriented knowledge gathering, with examples from both on land and at sea.
The chair of the Biodiversity Council, Signe Normand, began by discussing the prospects for a Danish biodiversity law, including how such a framework law could provide the basis for regulations regarding invasive species as well as, of course, the many other objectives for Danish nature. The proposal for a biodiversity law was first presented at Christiansborg on November 23, 2023, and it is the Council’s position that Denmark should assume its share of responsibility regarding, for example, the protection of 10% and 30% of land and marine areas, as proposed by both the EU and the UN Kunming-Montreal Agreement.
Jane Behrens, a senior researcher at DTU Aqua, presented decades of research on the marine invasive species black-mouthed goby under the title “From Research to Management: Knowledge About the Species’ Effects, and What Can We Do?” One interesting course of action presented by Jane Behrens was the possibility of commercially exploiting the goby, which could help keep the population in check, as it is not considered likely that the species can be eradicated.
Henrik Glenner, a professor at the University of Bergen, then explained how the native flat oyster—also known as the Limfjord oyster, a delicacy — has been facing very difficult conditions following the arrival of the invasive Pacific oyster, which is believed to have arrived here via ballast water from cargo ships. At the same time, the invasive Pacific oyster has brought other unwelcome guests with it—including the Asian oyster borer snail, which also preys on oysters, as well as an oyster parasite. In addition, a number of other invasive species are likely on their way, Henrik Glenner explained, concluding that Denmark’s lax attitude toward invasive species poses a problem for neighboring countries, because monitoring and early control are absolutely crucial.
Raccoon Dogs and Invasive Plants
Henrik Lange and Per-Arne Åhlén, from the Swedish Environmental Protection Agency and the Swedish Hunters’ Association, respectively, provided an overview of Sweden’s efforts to control invasive mammals and birds. The main message was: “Do or do not—there is no try,” which was in line with the presentation by biologist and owner of Care4Nature, Hans Wernberg’s presentation on combating invasive plants in Denmark—namely, to combat them 100% once you’ve decided to take action.
In Sweden, there is a team of hunters who are contractually obligated to respond within 24 hours after an invasive bird or mammal is reported. This has resulted in the effective control of raccoon dogs, mink, musk rats, and Egyptian geese, while a campaign against house martens has now also been launched. One challenge, according to Henrik Lange and Per-Arne Åhlén, is that once the control efforts are successful, it can become difficult to secure funding for a hunter corps to continue the control efforts—which was nonetheless crucial for staying ahead of the curve and preventing the spread and establishment of these species. Furthermore, the Swedes reported that Swedish hunters had unrestricted access to all areas when it came to pursuing individuals of an invasive species, in contrast to the situation in Denmark.
Later in the day, Mariann Chriél presented the authorities’ perspective from the Danish Environmental Protection Agency’s standpoint, focusing on prioritization, communication, and the control of invasive species in Denmark. The national budget has allocated 11 million Danish kroner; property rights are respected in Denmark; and there is not the very rapid response time to reports of invasive species that one sees, for example, in Sweden.
Find and download the symposium presentations as PDFs here
Target 6 of the UN Kunming-Montreal Agreement includes a goal to reduce the rate of introduction and establishment of invasive species by 50%, as well as a commitment to eliminate and control, in particular, priority established invasive species—both generally and at priority sites. This objective undoubtedly requires stepping up efforts in many countries around the world, including Denmark, with a focus on prevention rather than treating symptoms—since scientific research shows that by then it is often too late.
IPBES in Denmark would like to thank the symposium participants for attending and engaging with the technical content. A big thank you also goes to the 15 June Foundation and, not least, the symposium speakers.
