Anticipating the impact of biological invasions in the light of climate change
Results & impact4 June 2025
Competition for light, changes in soils, hybridization between plants, and so on... Invasive exotic species are one of the main causes of biodiversity loss. To protect against this, it is vital to identify the zones at risk. For the first time, scientists have produced maps of the risks posed by exotic species, based on their impacts and on climate forecasts. The study concerned acacias, trees that are proving invasive in South Africa.
Acacias are a threat to the flora of South Africa, particularly the fynbos biome, the only plant formation of its type in the world, which is characteristic of the South of the country.
The maps produced predict the changes in the impacts of Australian acacias up to 2100, depending on several IPCC climate scenarios.
The impact of these trees on the local wildlife is likely to decrease across half of the country, but increase in other zones. It is those zones that should be a priority for the authorities.
Until very recently, the distribution of an invasive exotic species was the main indicator for determining the threat to biodiversity. However, the mere presence of an invasive species does not necessarily mean a threat to the local flora or wildlife. As Océane Boulesnane-Guengant, a PhD student at ÁùºÏ²Êͼ¿â specializing in biological invasions, says: "Since 2020, we have had the EICAT standard, which pinpoints the impacts of invasive exotic species. That standard allows us to determine the danger to ecosystems much more accurately".
The differences between the presence and impact of invasive exotic species are clearly documented on a scientific level. However, risk maps have very rarely been produced to predict the impact over time. In an innovative study co-authored by Océane Boulesnane-Guengant, scientists were able to produce impact risk maps for Australian acacias depending on expected climate change in South Africa between now and 2100.
Map of acacia distribution in South Africa, alongside an impact risk map. Some zones are at high risk despite low numbers of acacias, and vice versa. Source: Boulesnane-Guengant, O. et al. 2025
Mapping changes in risks
Different climate scenarios were considered: optimistic, with a small increase in temperature, and pessimistic, with a substantial increase. Depending on the changes in climate conditions, the scientists were able to produce maps predicting the presence or absence of acacias by 2100. Océane Boulesnane-Guengant explains: "On top of this initial level of information, we added other indicators such as the level of impact or the impact mechanisms involved, such as competition for resources depending on the native species already present".
The results obtained show that the impact of Australian acacias is indeed likely to change as a result of climate change. Across 51.4% of the country, the risks are expected to fall by the end of the century. However, they will probably increase elsewhere, across an estimated 26% of the country.
Risk map for protected areas in Cape province, South Africa. In blue, zones in which Australian acacias should have less impact on biodiversity by 2100. In orange, zones where their impact is likely to increase. Source: Kumschick, S., Journiac, L., Boulesnane-Genguant, O. et al. 2025
A pessimistic scenario (an increase in temperature of more than 5°C), would see the trees spread very rapidly, with huge impacts on the local flora.
Prioritizing the zones likely to be impacted most serves to allocate human and financial resources more effectively. This is crucial for protected area managers, who have limited means. Océane Boulesnane-Guengant hopes that the method tested for Australian acacias in South Africa will gradually become standard procedure: "Climate change makes fighting biological invasions an even more uncertain undertaking. The EICAT standard is a big step forward, and we need to be able to include it in our forecasts".
Océane Boulesnane-Guengant is also working on invasive plants in Réunion. The issue on the island is a particularly pressing one: with 129 recorded invasive exotic species, it is one of the ten most invaded territories in the world. For the time being, the scientist is focusing on building risk maps based on impact, without considering climate change. Those maps serve as decision support tools for the managers of the Natural Park, who use them to target their operations on the most at-risk zones. This work is part of the ReMiNat (restoration of natural areas) project jointly headed by the University of Réunion, the National Park and ÁùºÏ²Êͼ¿â.
Managers of natural areas in Réunion have recently implemented a common protocol for assessing the degree of ecosystem invasion by exotic species. This new method, which can be adapted to several types of vegetation, enables accurate and rapid surveys. The tool is aimed at improving coordination in the fight against invasive alien species on the island, an urgent issue for this territory, which has one of the highest levels of invasion in the world.
References
Kumschick, S., Journiac, L., Boulesnane-Guenguant, O. et al. 2025. . Biol Invasions 27, 43.
