As wildfires burned through 3,200 acres of land on the Hawaiian island of Maui earlier this month, ultimately killing at least 115 people and destroying the city of Lahaina, some observers noted that the dry grasses that colonial occupiers introduced in the place of Hawaii's natural forests made the fires spread faster than they would have if the land had been left intact.
On Monday, a study resulting from nearly five years of research by experts from 49 countries revealed how the grasses are among thousands of harmful invasive alien species that have been introduced by human activities and placed communities across the globe at risk, with the human-driven climate emergency often exacerbating the negative impact of invasive plant and animal species.
The report by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), titled the Assessment Report on Invasive Alien Species and Their Control, catalogues more than 3,500 harmful invasive species that are already "seriously threatening nature, nature's contributions to people, and good quality of life," with Indigenous communities facing the greatest threats.
The harmful invasive species are among 37,000 alien species that have been introduced by human activities such as colonization and trade, and that number is "now rising at an unprecedented rate," according to IPBES, making it likely that the species' harms will grow.
"The future threat from invasive alien species is a major concern," said Prof. Helen Roy, co-chair of the assessment and a researcher at the U.K. Center for Ecology & Hydrology. "Thirty-seven percent of the 37,000 alien species known today have been reported since 1970—largely caused by rising levels of global trade and human travel. Under 'business-as-usual' conditions, we project that total numbers of alien species will continue to increase in this way."
"But business-as-usual is actually unlikely," continues Roy. "With so many major drivers of change predicted to worsen, it is expected that the increase of invasive alien species and their negative impacts, are likely to be significantly greater. The accelerating global economy, intensified and expanded land- and sea-use change, as well as demographic changes are likely to lead to increases in invasive alien species worldwide... Climate change will make the situation even worse."
The report, which includes "very significant contributions from Indigenous peoples and local communities, making it the most comprehensive assessment ever carried out of invasive alien species around the world," found that nearly 80% of the documented impacts of invasive alien species on nature's contributions to people are negative, particularly as food supplies are damaged. The Caribbean false mussel, which researchers believe traveled from its native South and Central America to India via ships, has damaged local fisheries while the European shore crab has been blamed for the collapse of shellfish industries in New England.
In addition to damaging people's livelihoods, invasive species such as the Aedes albopictus and Aedes aegyptii—types of mosquitoes—can spread diseases such as malaria, Zika, and West Nile virus.
The global economic cost of invasive alien species has quadrupled every decade since 1970, exceeding $423 billion in 2019.
Invasive species are also a major driver of the majority of global plant and animal extinctions, and "the only driver in 16%" of extinctions recorded by IPBES.
"At least 218 invasive alien species have been responsible for more than 1,200 local extinctions," said Prof. Anibal Pauchard, co-chair of the study and an investigator at the University of Concepción's Institute of Ecology and Biodiversity. "In fact, 85% of the impacts of biological invasions on native species are negative."
For example, Pacific oysters—intentionally introduced in the North Sea in the 1960s to compensate for the loss of Indigenous oysters and support commercial fisheries—have overtaken mussel beds in the region, affecting the seabirds that feed on mussels and microorganisms living between them.
The researchers emphasized that having introduced invasive alien species to ecosystems around the world, humans have the power to mitigate the damage done by the species.
The report suggests prevention measures such as border biosecurity and import controls, which have been effective in reducing the spread of the brown marmorated stink bug in Australasia, and public awareness campaigns such as "Check, Clean, and Dry" in the U.K., which encourages people to check their boating equipment for aquatic animals or plants before leaving the water, clean equipment thoroughly, and dry it before using it again.
Inger Andersen, executive director of the United Nations Environment Program (UNEP), said the report fills "knowledge gaps" that remain around invasive species, as the effects of over-exploitation, climate change, and pollution on biodiversity are relatively well-understood.
"By providing critical information on trends in invasive species and policy tools to address them, this report can provide a springboard to concrete action on invasive species," said Andersen. "I ask all decision-makers to use this report's recommendations as a basis to act on this growing threat to biodiversity and human well-being."
