The war on mimosas smells of pesticide and tiredness. “Our grandparents planted them for the vineyard, they didn’t know they left us a plague”, reflects with regret the president of the Ridimoas Association, Pablo Rodríguez, with his hands still tired from the effort. A few hours before I was cutting acacia trees in the O Ribeiro mountain, as they have been doing in the entity for more than 40 years … and in the next 40?
The truth is that new solutions are constantly being sought in the battle against this invasive species. No wonder: the latest National Forest Inventory estimates that Mimosas, or Acacia dealbata, occupy almost 1,790 hectares in the province of Ourense alone, and – despite the fact that the Galician Forestry Law prohibits planting it – its presence continues to increase. “It’s a tremendous problem,” summarizes Rodríguez.
The peculiar arms race against this plant enemy has several fronts, from the university to the forest communities or environmental associations. “The challenge we have is to eliminate acacias and at the same time favor the recovery of the natural flora; we must get native species to compete better than invasive ones”, Explains the professor at the University of Vigo Luis González, who has thoroughly studied the presence of acacias in the Ourense mountains.
Debarking, an ecological method
The community members of Mount Lobeira, in Vilanova de Arousa, ran into a problem: an acacia forest had grown on a spring that supplies the nearby towns, so using the usual pesticides -which are toxic to humans- was not One option. “A colleague had told me about a method that could help us in this case: debarking,” explains forestry engineer Carmen Rial.
The recipe is clear: you have to tear off the bark of each acacia, from the ground up to 1.30 meters high -at chest height-, with the aim of cutting off the flow of sap. “The effects take a while to be seen -develops Rial-, in a week the leaves already change color, and after a year the acacias are dead and dry, ready to cut down.” The key, he adds, is to ensure that the roots are dry, so that the plant does not regrow.
In Mount Lobeira they are now at this point, and they are optimistic about the process – “the fact of not applying chemical products is already good, it is more respectful of nature,” says Rial – and with the expected result. The environmental association Adega corroborates the good results: “We have been debarking for 12 years, not the Tea River and we have the results, but -in addition, we advocate for the least possible use of chemical products- we understand that there are areas of Ourense with such a concentration of mimosas that there are to undertake various methods, “says Ramsés Pérez, environmental educator of the entity.
Professor Luis González agrees in the assessment – “In our experience, the technique of barking has a 100% effectiveness in young trees, between five and six years,” he says, but points out another drawback: “It takes a lot of time and hand of work; that is, a lot of money ”. Therefore, communities in the areas most affected by the spread of mimosas are skeptical of the technique. Rodriguez, from Ridimoas, points out that in his area acacias number in the millions: “We did a lot of tests, but with these figures we have to be practical,” he laments.
From the drill to the salt water
Debarking is not the only avenue being explored as an alternative to chemicals. Another technique explored by UVigo is cCut the plant to the height of the cane and apply the herbicide directly. “You end up with the plant in question and around the year,” says González, but comments as an inconvenience that it cannot be carried out in very large areas, since it requires applying the product quickly, with the tree just felled.
“Another technique is with the drill: you make a hole and apply the product inside, which is much more effective and faster than the previous ones,” he explains. Looking to the future, Gonzalez puts his hopes in the “promising results” they are getting in experiments that replace the herbicide with salt water, which greatly reduces the cost.
However, the biologist warns that “the field is very different from the experimental plots”, a statement with which they agree from Ridimoas: “At the moment we have not found any alternative solution that will serve us”, concludes Pablo Rodríguez.
A century and a half of continuous expansion
In a short time, a road trip along the banks of the Miño will be marked by the intense yellow of the mimosas in bloom, a landscape so characteristic of several areas of the province that many residents may think that these trees have always been there. The reality, however, is that the mimosas entered Ourense 150 years ago, and since then they have been expanding, invading the land of oak and chestnut trees and damaging the plant and animal biodiversity of the province.
“As acacias compete for less resources than the Galician autochthonous varieties, and also change to the constitution of chan, or that makes it difficult for local flora to grow”, highlights González. Acacials create lush, impenetrable spaces where other plants will not grow. They are also trees with a prodigious capacity for reproduction, through their roots and seeds: “You have to be constantly cornering and cutting, it is impossible to end them,” says Rodríguez. The war against acacias, for the moment, does not seem to have an end.