In nature too, hell is sometimes other people. Invasive alien species, introduced by man, are spreading more and more rapidly in the world, causing enormous damage. A tidal wave in the face of which humanity has so far proved relatively powerless. Asian hornet, American crayfish but also ragweed, Japanese knotweed or cute squirrels and raccoons: invaders proliferate, favored by globalization or climate change, ravaging crops and forests, spreading diseases and threatening the quality of life on earth. To assess and counter this “immediate emergency”, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), nicknamed the IPCC for Biodiversity, published Monday, September 4, an unprecedented report, a synthesis of more than 13,000 studies carried out by 86 international experts from 49 countries.
There are 37,000 exotic species (introduced by man into a territory) in the world. Less than 10% (3,515) are considered invasive, meaning there is “evidence” of the “adverse, and in some cases irreversible, effects” they cause, according to this panel which advises the United Nations Convention on Biological Diversity (CBD). Among these public enemies, 6% are plants, 22% invertebrates, 14% vertebrates and 11% microbes. Invasive species are a serious threat to biodiversity: they play a “major role” in 60% of extinctions and in 16% of cases they are even the sole cause.
Their main misdeeds are to upset ecosystems (27%), to compete with native species (24%) or predation (18%), according to the IPBES which warns “about the cascading effects”. Case in point: the recent deadly fire in Maui, Hawaii was fueled in part by plants imported for livestock feed, which spread through abandoned sugar plantations. Because invasive species also have a negative impact on humans, affecting “livelihoods, food security, access to water, economy and health”, the report points out.
The list of damage is long: American forests ravaged by Asian jumping worms, seagrass beds greedily eaten by rabbitfish in Turkey, a vicious circle linked to the introduction of Nile perch into Lake Victoria described in the documentary Le Darwin’s Nightmare, etc. In 2019, their overall cost was estimated at $423 billion, the equivalent of the GDP of Denmark or Thailand. A “probably greatly underestimated” amount, which has quadrupled every decade since 1970.
Nicknamed “silent killer”, such as Batrachochytrium dendrobatidis, a microscopic fungus that breaks down the skin of amphibians; “green cancer” like Miconia calvescens, a Mexican tree that threatens Tahitian forests; or disease-carrying “plague”, such as the tiger mosquito… Invasive alien species result from deliberate introductions but also from simple accidents. The Mediterranean is teeming with non-native fish and plants, such as lionfish and so-called “killer” algae, which have traveled as stowaways in the holds of cargo ships from the Red Sea via the Suez Canal.
Europe, the Americas and Central Asia are home to the greatest concentrations of these pests. And islands and indigenous peoples highly dependent on nature are particularly vulnerable. “Threats related to biological invasions are growing at an unprecedented rate around the world and, for sure, things will get much worse,” Helen Roy, one of the three publication co-chairs. If nothing is done, the IPBES estimates that their number will have increased by 36% in 2050 compared to 2005.
However, the fight is not lost in advance. “Managing biological invasions is realistic and achievable, with substantial benefits for nature and people,” said the IPBES, which lists three lines of defense: prevention, eradication and containment, the first remaining “the most cost-effective option”.
But you still have to tackle it. So far, only 17% of countries have adopted national strategies to tackle the problem head-on and nearly half (45%) are doing nothing, it says. “The cost of inaction is really high,” said Anibal Pauchard, co-chair of the report. “Humans are at the heart of the problem but they are also at the center of the solution,” adds Helen Roy. The Kunming-Montreal Agreement, adopted by the international community at the end of 2022, sets the goal of reducing the rate of introduction of invasive alien species by 50% by 2030. According to Anne Larigauderie, Executive Secretary of IPBES , this commitment is “essential, but also very ambitious”. The report provides “the necessary evidence, tools and options” to make it “more achievable”.
