University of Vienna: The global loss of floristic uniqueness

If alien plants are introduced and successfully spread in a region, it can have significant negative consequences for native species. Apart from that, another aspect of the global spread of plant species, is that this process also leads to a standardization of regional floras and thus to a loss of uniqueness; an effect, that has rarely been studied so far.

Investigation using global databases

In their current study, published in Nature Communications, the researchers used global databases to compare the composition of 658 regional floras from almost all parts of the world for the first time. In addition, they investigated the influence of natural and man-made factors on the increasing uniformity of regional floras. To assess the uniqueness of individual regions, they considered both the number of plant species a region shares with other regions and the degree to which plant species are related to each other. In doing so, they also included regional evolutionary history in their study.

Biogeographic factors play an important role in the spread of alien plants and the loss of uniqueness of regional floras. These include the geographic distance between the regions considered and their climatic differences, according to the study. “A plant can establish well in a new region if the climatic conditions in the area of origin and the new area are similar,” explains biodiversity researcher Franz Essl of the University of Vienna.

Political factors as additional driving force

But man-made factors have an influence on the spread of alien plants and the standardization of regional floras worldwide as well. For example, the researchers describe that a common political past also plays a role: Regions that formerly belonged to a common state show greater uniformity in the species composition of their floras. This effect can also be seen within existing national borders, such as within the single states of the USA. Historical examples include European colonial powers and territories formerly occupied by them. “The colonial powers also introduced plant species into their former colonies – either intentionally as trade goods or as useful plants, but also unintentionally,” explains biodiversity researcher Bernd Lenzner of the University of Vienna, co-author of the study.

The need for more effective biosecurity measures

The bottom line is that alien plants are driving the global standardization of regional plant communities, and humans are a major contributor by further spreading them. “We need more effective biosecurity measures against the continuing spread of alien plants to preserve the uniqueness of our habitats” concludes Franz Essl.

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