Lot: when exotic species invade the department


the essential
Many exotic species can be observed more and more in the Lot: animals but also plants… Focus on the specimens that are found most frequently in the department.

An exotic species, quèsaco? More commonly called “invasive”, these are specimens that have been introduced into the department, voluntarily or not, when they are not part of the local biodiversity. Often, they have a negative impact on native species (well established in the department). Update on these animals and other plants.

Like a fish in water

The waters of the Lot, mainly the lakes, are populated by more or less large exotic fish and shellfish. Starting with California crayfish. These little creatures live in the same type of habitat as white-clawed crayfish, which are a very Lotoise species. The first are carriers of a healthy disease which kills the second. A slight source of concern for the Lot Fishing Federation.

On the fish side, the catfish landed from the Danube. When he arrived, “there was a wave of panic. “Some thought they were going to eat everything in their path”, explains Laurent Fridrick, technical manager at the Federation. But these individuals, who can measure more than 2 meters, “It’s just another predator added to the food chain,” concludes the scientist.

There are two other species introduced by man: sunfish and catfish. The latter is in clear decline in the Lot.

Plants in the flora…

Let’s talk little, let’s talk plants. Jérôme Dao, invasive alien plant project manager at the Conservatoire Botanique National Midi-Pyrénées et Pyrénées, notes that most of the exotic plants that invade the Lot upset the biodiversity of the department. A large majority of them come from America, and were brought back involuntarily (contaminated seeds) or voluntarily (related to a use: garden, development and decoration of pond…).

Datura, nicknamed “devil’s grass”, is a species that has an impact on health: it can cause moderate or severe poisoning for several days. Very small amounts are enough to trigger a reaction. Avoid handling them by hand at all costs.

There is also mugwort ragweed which arrived through contaminated sunflower seeds. More and more agricultural sectors are affected by the invasion of this plant, with up to 80% loss of yields on sunflower farms.

…but also in the aquatic environment

The aquatic environment is not spared by these invasive plants. We can cite the negundo maple. It is a tree that was introduced voluntarily. Its seeds fly very easily and leave the plantations where they were to land on the banks of watercourses. “It’s their favorite environment,” says Jérôme Dao. The negundo maple is very present in riparian forests (vegetation on the edges of waterways), and can quickly take precedence over the other species present (such as ash). “The biggest risk is therefore to have a non-diversified riparian forest. But we don’t know how the maple will react to global warming, or if a disease arrives?” asks the researcher, at the risk of the Lot riparian forest.

In the Lot, there is also a lot of watermilfoil, especially in isolated ponds. In Dégagnac, the Palazat stream is almost 50% covered with it. If it gets too big, it risks ending up in the Lot, and that will surely not be good news…

Jérôme Dao does prevention: you have to find out about any species before planting them. “The Conservatory is there for that. People can call us if they have any doubts, or even any other biodiversity actor, he explains. Avoiding planting invasive species is the biggest part of the fight .”

Focus on insects

On the insect side, it is possible to meet the box tree moth, the plane tree tiger, but also the Asian hornet. How did these little critters develop? If we take the example of the hornet, the latter would have arrived in Lot-et-Garonne in 2004 by plane. But there are other ways: insecticide products that can disrupt biodiversity, global warming, monoculture or even perennial cultivation (they do not allow soil renewal and therefore the pest always has everything it needs) .

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