Invasive plants, a threat to biodiversity

Some of these so-called "invasive species" threaten the development of local species.

Daniel Onea, 26.09.2025, 14:00

A silent but extremely deadly enemy is gaining ground in Romania’s natural ecosystems. Known as “non-native invasive plants”, these species pose a real threat to endemic biodiversity, with profound economic and ecological effects. From the banks of the rivers in the Făgăraș Mountains to urban spaces, exotic species, once admired for their beauty, are now becoming a destabilizing factor. To better understand this complex phenomenon, we spoke with biologist Oliviu Pop from Conservation Carpathia Foundation. What exactly is an invasive plant? It is not just a flower brought from another continent. The process is much more complex and is closely linked to human activity.

“A species can be considered non-native when it does not naturally belong to a continent, a country or a biogeographic region and has been introduced there due to human activity. This can happen either deliberately, such as plants that were originally cultivated in gardens, or accidentally, such as the seeds of plants brought with other agricultural products. When they have naturalized, that is, they have begun to multiply on their own, to produce fertile seedlings, some of them begin to emerge in nature, to invade very large areas and then they are called non-native invasive plants”.

The real problem arises when these species, deprived of natural predators in their habitat of origin, start to multiply exponentially. They manage to quickly cover large areas of land, suffocating and eliminating the local flora, which is essential for the balance of the ecosystem.

“The problem with these plants is that they multiply very quickly, manage to cover very large areas of land in a short time and eliminate native species of importance for biodiversity, medicinal plant species, fodder plant species and so on. So, they become monodominant. The problem is not that we have another flower, another beautiful plant in our fields and forests, but that these plants are so aggressive that they eliminate all the others, including the associated fauna species”.

At national level, the situation raises concern. Over 100 such species with invasive potential have been identified. In the area of ​​the Făgăraș Mountains, the Foundation’s team initially identified seven particularly dangerous species, but their number is constantly growing. One of the most aggressive is, without a doubt, the Japanese knotweed. This plant not only eliminates the competition, but has an extraordinary destructive force, which can even affect infrastructure.

“We focused on a species that is one of the most dangerous, the Japanese knotweed (or Reynoutria japonica), which can occupy very large areas, eliminate all endemic species, and even prevent forest regeneration along rivers. It has the ability to grow through asphalt, if asphalt is poured and the roots of this plant are not removed, or through the floors of houses, if houses are built and there was an invaded area there. Therefore, it affects both biodiversity and the economic value of meadows, forests, and even the real estate value of land”.

The fight against these species is difficult and long-term. The European Union has issued a directive that obliges member states to identify and control the spread of these plants. At local level, organizations such as Conservation Carpathia are implementing concrete projects. The management of invasive plants has become an essential component of the ecological reconstruction activities of degraded habitats. In Rucăr, an awareness-raising event took place, where locals could see firsthand the impact of Japanese knotweed and learned how they could contribute to keeping it under control.

“The event we organized was a demonstration, an awareness-raising activity designed to involve local communities in the management of non-native species. It took place along a river, Râușor, which was heavily invaded by this species. Together with colleagues from the Foundation, we demonstrated to the locals who participated, children and some representatives of the media, how this species can be kept under control by cutting it regularly. We also explained and they were able to see, practically, on the ground, what an area invaded by Japanese knotweed looks like”.

Although the problem sometimes seems overwhelming, biologist Olivio Pop emphasizes that each person can play a crucial role in limiting this phenomenon. Awareness starts in their own garden, and a seemingly small gesture, such as responsibly disposing of plant debris, can make a huge difference. Prevention is the most effective method, because once an invasive species takes root over a large area, its eradication becomes almost impossible.

“First of all, people should be informed. Locals should stop growing these potentially invasive plant species in their gardens, because this Japanese knotweed was originally a beautiful plant grown in gardens. It can grow up to three meters high. The roots reach up to 30 meters. That’s why it’s so dangerous! And, first of all, when cleaning gardens, throw away the plant debris, do not throw it on the banks of rivers or in nature. Because this is the primary source of the appearance of these non-native invasive species in nature, in our project area. Locals have thrown away garden debris, with the roots or seeds of these plants, on the banks of rivers”.

Invasive plants deeply affect ecosystems. They cause huge economic losses in agriculture and forestry and can irreversibly degrade entire habitats, affecting food chains. Their accelerated spread through trade and tourism has transformed this phenomenon into a global ecological crisis, difficult to manage. (VP)