Acacia dealbata is no ordinary newcomer. Native to the temperate coastal zones of south-eastern and south-western Australia and to Tasmania, the species was introduced to Europe in the late 1700s as an ornamental plant and as a source of fuelwood and construction timber. Since then it has become one of the most successful invasive trees on the continent, particularly in the Iberian Peninsula and the Mediterranean basin. It is officially listed as an invasive alien species in Spain and Portugal, and several of its relatives, including Acacia saligna, appear on the European Union’s list of invasive alien species of Union concern. France and Italy, both hotspots for acacia proliferation, have so far refrained from specific legislation targeting the genus, largely because the cut-flower and perfume industries depend on it.

The secret to the silver wattle’s success lies in a formidable arsenal of ecological traits. It grows rapidly, shading out native competitors in the race for sunlight. Its extensive root systems deplete soil water, starving neighbouring plants of a scarce resource. It is a generalist in terms of nutrient availability, thriving where fussier species struggle. It resprouts vigorously after disturbance, produces allelopathic leachates that chemically suppress rivals, and fixes atmospheric nitrogen through its leguminous symbiosis, enriching soils in ways that can favour its own kind over native flora adapted to poorer ground. Crucially, it is remarkably resilient to bushfires and elevated atmospheric carbon dioxide, meaning that the very disturbances amplified by climate change may work in its favour rather than against it.

To map where this invader might strike next, the research team, led by Pedro Lago-González, built maximum entropy models, a widely used statistical framework known as MaxEnt that estimates the most uniform probability distribution consistent with known species occurrences. The team compared the climatic niche of Acacia dealbata with that of Quercus robur, the pedunculate oak, a defining species of temperate broadleaf deciduous forests in Europe and western Asia and a representative of habitats highly sensitive to acacia invasion. Occurrence records came from the Global Biodiversity Information Facility, while climate data spanning 1963 to 2023 was drawn from the NCEP/NCAR reanalysis project, with future projections taken from the CESM2 Earth system model under four shared socioeconomic pathways, ranging from the optimistic SSP1-2.6 to the severe SSP5-8.5.

The technical pipeline was deliberately rigorous. Rather than feeding raw climate data into the models, the researchers engineered a physically meaningful set of predictors: mean values representing baseline conditions, annual ranges and seasonality indices capturing periodic variability, and empirical orthogonal function components describing interannual climate variability. Isothermality and daily thermal range were included for temperature, while precipitation was summarised through annual accumulation, seasonality, and monthly extremes. Species occurrence data was cleaned of duplicates and offshore records, spatially thinned at a 25-kilometre radius to counteract uneven sampling, and background points were generated with a global accessibility weighting to mimic sampling bias. The models were trained with fivefold cross-validation and evaluated with area under the curve metrics, achieving values above 0.90, a level of performance consistent with previous acacia distribution studies.

Temperature emerged as the dominant force shaping the silver wattle’s distribution. Average temperature alone contributed 42 percent of the model in the earlier period and, by permutation importance, 39 percent in the later one, with temperature seasonality also playing a major role. The response curves tell a striking story: suitability for Acacia dealbata climbs steadily as average temperature rises, peaking between roughly 13 and 20 degrees Celsius before collapsing near 25 degrees. The oak, by contrast, prefers cooler conditions, with its modelled optimum centred near 8 to 9 degrees Celsius. The two species share a remarkable 9.9 million square kilometres of territory, mostly in the mid-latitudes, yet their climatic profiles differ significantly for nearly every variable. Acacia tolerates a wider amplitude of daily temperature range and endures more contrasting precipitation regimes, including drier minima and greater precipitation seasonality, than the oak.

The overlap between the two niches is quantified through Schoener’s D and Hellinger’s I, indices that measure how closely two probability distributions coincide across a landscape. Both indices rose between the two historical periods, with Schoener’s D climbing from 0.26 to 0.34 and Hellinger’s I from 0.55 to 0.61. The principal hotspot of this overlap is western Europe, especially northern Spain and France, where oak forests and silver wattle already coexist uneasily. Secondary hotspots include the south-eastern Australian coast, New Zealand, and stretches of the Pacific coast of the Americas. Notably, the spatial pattern of overlap changed little between periods; rather, it intensified in the very places where it was already established, suggesting a concentration of conflict rather than a wholesale relocation.

The future projections are where the study delivers its most consequential warning. Under the mildest scenario, SSP1-2.6, silver wattle suitability in Europe remains confined to a few Atlantic coastal fringes of the south-west. But as radiative forcing increases, so does the European footprint of the species. Under SSP2-4.5 and SSP3-7.0, suitability expands markedly across Mediterranean Europe, with the probability of occurrence increasing by more than 60 percent in some Mediterranean areas. Under the most severe scenario, SSP5-8.5, the species’ climatic niche shifts dramatically northwards, reaching the British Isles, with the Irish Atlantic coast highlighted as particularly suitable. Meanwhile, oak suitability behaves differently: rather than simply declining with forcing, it migrates towards the poles, concentrating under high-emission conditions along Scandinavian Atlantic coasts and the northernmost territories of Ireland and Scotland. Niche overlap between the two species generally increased with radiative forcing, with the strongest overlap under SSP5-8.5 concentrated over north-western Europe and the mid-latitude Pacific coast of South America.

The authors are careful to spell out the limitations of their approach. MaxEnt assumes that species spread to an equilibrium state consistent with the climate, which is rarely true in practice, and the model considers only climatic variables, omitting soil characteristics, land use, biotic interactions, and the socioeconomic forces that drive introductions. The relatively coarse climate grid, interpolated to a finer resolution, may smooth environmental gradients and inflate suitable areas. Nor can the model distinguish between areas that are climatically suitable but not yet reached by the species and areas that become newly suitable under climate change. Interestingly, the study also found that acacia suitability decreased in some regions, such as southern Brazil, for reasons that neither climate shifts nor human intervention readily explain, a puzzle the authors flag for future research.

Nevertheless, the management implications are clear and urgent. The researchers argue that invasion prevention should look not only at where Acacia dealbata currently thrives but at where it could thrive tomorrow. Countries such as France, the United Kingdom, Italy, and Croatia cultivate the species ornamentally, and the study suggests these nations could face growing establishment risk, particularly under stronger warming. Rather than outright bans, which the authors acknowledge may be excessive, they advocate early surveillance programmes, noting that the species can already be detected by remote sensing combined with machine learning algorithms, a cost-effective route to operational monitoring. Riparian ecosystems deserve particular attention, as the species aggregates along watercourses that serve as dispersal corridors. Rapid response plans, they argue, should be designed now for uninvaded areas that may become vulnerable as temperate zones shift. In a warming world, the front line of the battle against biological invasions is moving north, and the silver wattle, with its fire-forged resilience and nitrogen-fixing ambition, is following the heat.

Subject of Research: Projected effects of climate change on the global climatic niche and potential distribution of the invasive tree Acacia dealbata in temperate forests

Article Title: Projected climate change could expand the geographical suitability of Acacia dealbata into new temperate areas

Article References: Lago-González, P., Acuña-Alonso, C., & Álvarez, X. (2026). Projected climate change could expand the geographical suitability of Acacia dealbata into new temperate areas. Environmental Monitoring and Assessment, 198(10), Article 1131. https://doi.org/10.1007/s10661-026-15951-5

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15951-5

Keywords: Acacia dealbata, invasive alien species, species distribution models, MaxEnt, climate change, Quercus robur, temperate forests, climatic niche, CMIP6 scenarios, biological invasions, Europe, biodiversity conservation