A yellow tide threatens to poison the landscape of Catalonia.

Hidden amidst the pre-Pyrenean mountain ranges—the Cadí, Pedraforca, and Port del Comte mountains—lies the Vansa-Tuixent Valley, a delightful place steeped in forests, meadows, and villages frozen in time. And it is here, for the past four years, thatDefendemos la Vansa Association organizes grassroots raids with neighbors, ranchers, farmers, and vacationers to combat a seemingly harmless yellow flora—one of the 20 most dangerous plants in Catalonia—that has become a plague threatening to poison this natural setting and wipe out the local economy.

"We still have time to prevent it," asserts Daniel Siscart, who leads this initiative and coordinated one of the latest grassroots actions to expand the fields at the beginning of August.

This ecologist and biologist had been following the situation in the Cerdanya solana for years with concern, where large yellow patches can be seen in the pastures of Guils, Lles, Bellver, and Aransa in autumn; it also occurs in Andorra and other areas in the northeastern Pyrenees. That's why, when the first specimens began to appear in Vansa, all the alarm bells went off and he decided to take action quickly. He began organizing talks and workshops with the aim of raising awareness among the people of the valley about the environmental danger that this entails. Cape senecio (Senecio inaequidens) and promoted an action plan in certain areas where the plant was not yet established enough to begin digging them.

"They are plants from the same family as daisies (asteracias), widespread in Catalonia and the Iberian Peninsula," he explains. Joan Pino, director of CREAF and professor at the Autonomous University of Barcelona (UAB). "Many Senecios are native, but some have been recently introduced by humans and have become invasive," he adds. This is the case of the Cape Senecio, native to South Africa, which is toxic to livestock and harms local biodiversity. It is also a risk to human health, because it passes into foods such as milk, honey, eggs, herbs for infusions and teas, and aromatic spices, among others. And regular consumption is associated with liver toxicity and the risk of cancer.

The same thing happens with the Senecio pterophorus and heangulatus, which have been wreaking havoc for at least two decades in many natural areas of the coast and pre-coastline, such as the Llobregat Delta, Collserola, Montjuïc, and also in Garraf. Unlike the mountain delta, which blooms in autumn and winter, these other two more metropolitan ones bloom in spring.

"In June, if you walked through the Llobregat Delta, you could see the riverbed completely dyed yellow," says Pino, who identified individuals of pterophorus In the late 90s and early 2000s, when I was doing a study on the environmental impact that the airport's third runway would have. Since then, CREAF has been documenting how the plant has spread through the channels and floodplains of the Llobregat and Besòs rivers, reaching several natural areas, such as Montseny and Montnegre-Corredor.

The main hypothesis is that these South African species of Senecio arrived sometime in the second half of the 20th century linked to the wool trade. The plant scatters its seeds with a plume-like structure that causes them to fly—the typical white spheres that children blow in the fields—which helps the seeds become securely trapped in the sheep's wool. Textile industries in Europe imported wool, washed it in water from wells and rivers, and dumped the excess back into the environment. This led to the Senecio becoming established along riverbanks, gradually colonizing territory in Central Europe until it reached the Pyrenees, crossed them, and landed in our country.

So too, surely, appeared in Catalonia the pterophorus, first identified in the 1980s in the Vallès. Eva Castells, A researcher at the UAB and CREAF, an expert in plant toxicity, explains that it most likely entered through the Ripoll River, in Sabadell, where the first individuals were found. There, between Sabadell and Terrassa, was the largest textile industry in Spain, and scientists believe that this must have been the focus of the invasion. Unlike the Cape, pterophorus It grows in Mediterranean and more humid climates, which is why it is found on the Catalan coast, as well as in Australia and the northern regions of Italy adjacent to France.

Remove competition

As with many exotic species, in order to establish and colonize a new territory, the habitats must be degraded: areas that suffer frequent alterations, such as peri-urban environments where ditches are often dug to lay pipelines; areas that have been burned in fires; or abandoned crops or overgrazed meadows. "All of this," Castells explains, "generates windows of opportunity that these species take advantage of."

And added to this, Senecio also has a tremendous colonizing capacity. "When it settles, it has allopathic substances that prevent other plants from germinating. In addition, it produces an average of 10,000 seeds per plant, which gives it an extraordinary reproductive capacity," highlights Siscart, from the Vansa-Tuixent Valley.

A risk also for human health

"They displace other species, cause changes in communities and ecosystems, and lead to a loss of biodiversity, both in plants and in the organisms they depend on," Castells points out, and Pino adds that "they can confuse pollinators," in addition to being toxic to insects and herbivores. "The mountain one certainly is; pterophorus It is suspected that they may also, but we still don't know for sure," clarifies the director of CREAF.

The toxicity of senecios is due to the fact that they contain substances called pyrrolizidine alkaloids that affect the liver, especially in vertebrate animals, and can also cause injuries, CREAF researcher Eduard Pla.

Precisely, these substances make them bitter, which makes herbivores avoid eating them. repeated," insists Castells, who warns: "These toxic alkaloid substances can occur in cow's milk, or in chicken eggs. And they can also be present in honey, because they are also in pollen, or in infusions of herbs or aromatic spices."

In this sense, theEuropean Food Safety Authority, EFSA, has published several documents on pyrrolizidine alkaloids, both in human food and livestock feed, and has established a maximum allowable limit per kilogram of body fat per day to avoid the risk of developing cancer. "Every day they publish food alerts about the risk of alkaloids. There's no need to alarm the population, but neither is there a need to minimize the danger. There's a real risk that these substances, which don't degrade, will enter the food chain," warns Castells.

Control its expansion

Once an exotic plant has established itself in an ecosystem and is in the colonization phase, it is extremely difficult and expensive to eradicate. The experts consulted for this report agree that it is best to try to control it in particularly valuable areas and protected spaces, and to put considerable effort into the prevention and surveillance phases to prevent its arrival.

"Our experience from places where it has been present for a longer time tells us that the only thing we can hope for is to control it, but not to reverse its presence in the territory," says Pla, who is working on the European project. Life Pyrenees4Clima, which seeks to adapt the Pyrenees region to climate change. In fact, within the framework of this initiative, coordinated by the Pyrenean Climate Change Observatory (OPCC) of the Pyrenees Working Community (CTP), which has European funding, researchers advise farmers and ranchers to incorporate practices that control its spread and reduce the risk of poisoning.

"Often, farmers and ranchers, in good faith, but mistakenly, till the fields where they find it, or mow it, and this is a mistake that spreads it even further," warns Siscart. As if that weren't enough, senecio is also resistant to herbicides. So the only way to stop its spread, says this ecologist, is to "uproot" it; but this solution is not shared by the entire scientific community, which is studying different strategies.

Even so, on a small scale, in the Vansa Valley, it seems to be working for them. "If you pull up the plant, you'll see it again the following fall. But you have to be patient and do it for several consecutive seasons," explains Siscart, who emphasizes: "It's important not to touch the plant when it sets seed, between September and November. And pull it up and leave it there, or at most throw it where it will proliferate the most."

In the areas of the valley where they've taken action, they're beginning to see results, while in the rest of the valley, the senecio is spreading like an oil slick, destroying native grasses and herbs like lavender, savory, hyssop, and thyme. "Many farmers who subsist on small farms, when they lose their pastures, give up. And with them, we lose the landscape and the socioeconomics. But we still have time to stop it," affirms this biologist, convinced.