Not only people and animals migrate to foreign habitats, plants also regularly settle in new areas with suitable living conditions. Some invasive plants have become particularly widespread in the Mediterranean region. A biologist has now examined in more detail why this is the case. The reason for this is the special properties of the invasive plants, but also the involuntary support from humans.
Again and again, seeds or other plant components find their way into new habitats through the air, through birds or via human traffic routes. Over time, some of these invasive plants successfully establish themselves in their new environment. In the worst case, they gradually displace the previously typical flora if it spreads less effectively than the newcomers. This development can be clearly observed, for example, in the ecosystems on the coasts of the Mediterranean, which have completely changed in recent years due to invasive plants.
How do alien plants get a new start?
Biologist Sergi Munné-Bosch from the University of Barcelona examined in more detail which strategies invasive plants use to establish themselves on the Costa Brava and other Mediterranean coastal areas. To do this, he analyzed how Carpobrotus, Acacia, Agave and Opuntia, which were not originally native there but are becoming increasingly common, reproduce. He first noticed that these plants have particularly good conditions for a new beginning. “The Carpobrotus are very resistant to climatic changes and show a perfect combination of clonal and sexual reproduction in order to be able to quickly colonize new spaces,” says the biologist, describing some of the advantages of the plant genus.
Additionally, these plants can create permanent seed banks that remain hidden underground for years before sprouting. This makes them very resistant and extremely difficult to get rid of. The plant genus Carpobrotus also includes several species, some of which are already able to form hybrids, reports Munné-Bosch. As a result, they are now so well adapted to the Mediterranean habitat that they can even colonize the ecologically special coast of Catalonia. Plants of the genus Opuntia are also now colonizing many Mediterranean coastal areas, including in southern France, using similarly sophisticated strategies, as the study shows.
Invasive plants had help from humans
But why do these foreign plants settle in the Mediterranean, of all places? To find out, the biologist compared the Mediterranean coastlines with each other. The result: wherever the flora changes particularly quickly, people are strongly present and active. “These biological invasions were caused by us humans by creating high dispersal pressure in these fragmented habitats,” says Munné-Bosch. By this he means that we have permanently changed the landscape through road and urban development, tourism and gardening. As a result, the natural habitats in the Mediterranean became increasingly fragmented, which made it easier for invasive species to settle and subsequently adapt, according to the biologist. According to this, humans involuntarily help invasive plant species to survive through their interventions.
At the same time, we humans have introduced many seeds or plant components either intentionally or accidentally. Not only the plants studied by Munné-Bosch, but many other invasive species have benefited greatly from human reintroduction, as historical records show. “Our lack of knowledge has meant that habitats in the Mediterranean are now particularly threatened by the presence of invasive plants and will never be the same again,” emphasizes the scientist.
More nature conservation needed
The problem is that new plant species that have already been established are difficult to get rid of because of their underground seeds. Munné-Bosch therefore recommends specifically destroying these seed banks. The development of the past few years probably cannot be completely reversed, but at least it can be stopped. In order to protect the environment and protect the remaining ecosystems from further invasive species, people will have to build fewer settlements and intervene less in nature in the future. “We need to prevent the invasion of colonizing plants where they have not yet been introduced through human intervention,” says Munné-Bosch.
“The unintentional introduction of a single plant into an unsuitable location from a conservation perspective can lead to major changes in our natural ecosystems and sometimes even destroy them. Preserving nature is therefore the best investment to preserve the existence of our species,” concludes the researcher.
Source: Sergi Munné-Bosch (University of Barcelona), Trends in Plant Science, doi: 10.1016/j.tplants.2023.11.007