These blue-violet fields that illuminate Icelandic postcards every summer are not a natural backdrop. They are the result of a biological invasion, launched by the state in 1945 with a handful of seeds from Alaska. The Nootka lupin (Lupinus nootkatensis) was intended to rehabilitate a bare volcanic soil. It eventually repainted the country. The photo is beautiful. The ecology, much less so. The Nootka lupin was imported from Alaska in 1945 to fix nitrogen and stabilize the eroded volcanic soils of Iceland. The plant spread freely in the absence of natural predators, colonizing up to 35 times more area in fifteen years in some regions. The lupin modifies the soil chemistry to favor its expansion and replaces the local flora with a dense monoculture, suffocating mosses and lichens. When the first settlers arrived from their longships more than 1,100 years ago, two-thirds of the island was covered with vegetation, and the Arctic fox was the only terrestrial mammal. After centuries of deforestation and grazing, there remained expanses of ash and black sand that the wind and rain carried toward the Atlantic. In the middle of the 1940s, the Icelandic Forest Service (Skógrækt ríkisins) was looking for plants capable of holding this soil. Its director, Hákon Bjarnason, spent three months in Alaska to bring back the plants and trees he thought could green Iceland. The lupin arrived in 1945, in a suitcase. Upon his return, Bjarnason told the press that with a little effort, Iceland could resemble much more the coastal Alaska, with large trees and plenty of blueberries. The choice of the lupin was not due to chance. This legume hosts bacteria that capture nitrogen from the air and store it in the nodules of its roots, which gradually enriches a soil that contains almost none. It also knows how to extract phosphorus from compounds present in poor soils. On paper, it was the ideal tool to prepare the ground for future forestation. A plant that no one eats, nothing prevents. The Nootka lupin contains alkaloids that make it bitter. The sheep, omnipresent on the island, avoid it. Without herbivores to graze on it and without any competing plants, it progresses freely. It forms dense stands about one meter high, whose foliage shades the soil and suffocates mosses, lichens, and low heaths. It even invades the understories of dwarf birch, to the point of eliminating small plants. The carpet of flowers is so dense that, in the heart of a lupin field, the soil is no longer visible. In some places in the east, up to 35 times more area in fifteen years. The figure comes from a study cited by the magazine Hakai, which notes that the plant mainly gains ground on areas already covered with local flora, and not on the bare sands it was supposed to stabilize. From heroes of restoration to undesirable species. The Icelandic Institute of Natural History (Náttúrufræðistofnun Íslands) today classifies the lupin among invasive species. The Ministry of the Environment has also declared it an "invasive exotic species." It is listed on a very short list, with only one other vascular plant, the wild chervil, and a moss. The reversal says something about the era. According to botanist Pawel Wasowicz from the institute, in 1945, no one knew the concept of invasive species, the term did not even exist. Free seed packets were distributed at gas stations to encourage planting. The balance remains nuanced, and researchers do not hide this. The introduction of the lupin has slowed erosion and desertification in some areas, while remaining controversial. In Heiðmörk, near Reykjavík, where it was planted early, the vegetation succession tends toward a rich grassland, often dominated by another invasive species, the wild chervil. The lupin thus prepares the ground, but not necessarily for the flora that was expected. An expansion that the climate may accelerate. Eradicating the plant is not on the agenda. Ecological restoration specialists consider this solution unrealistic, and authorities do not take serious measures to contain its spread. The uprooting campaigns have mainly proven the resilience of the lupin, whose long central root complicates any uprooting work. The damages to watch out for also concern insects: researchers from the University of Iceland have studied the effect of its stands on pollinators, including bumblebees, near Reykjavík. Global warming plays against managers. The areas with a climate favorable to the lupin should expand rapidly by 2050, with a risk of colonization of a large part of the central highlands. According to Hakai, at the current rate, the planted forest would cover about 1.6% of the territory by 2085, while the lupin could reach two digits. It is there, in the deserts of lava and ash in the center, that the next line of defense is taking shape: new barriers are being set up to slow its progress. Deserts that the lupin had precisely been chosen to conquer.