The range of rare plant species in the Alps is shrinking faster than that of widespread species. Especially in low-lying areas, rare and sometimes endangered species are increasingly competing with non-native plants. These are the results of a study by Italian researchers who were able to draw on data from 1479 plants and their distribution between 1990 and 2019. In lower areas, the habitat of the plants is also more severely affected by humans than at higher altitudes, writes the team led by Costanza Geppert and Lorenzo Marini from the University of Padua (Italy) in the journal "Proceedings of the National Academy of Sciences" ("PNAS"). .
"Our long-term, high-resolution dataset allowed us to account for a large number of native species, including rare native species, and alien species," the scientists write. The database used contains more than a million entries of plants that have been identified over 30 years at an altitude of 61 to 3456 meters above sea level. The study authors define “rare species” as those listed as “Near Threatened”, “Vulnerable”, “Endangered” and “Critically Endangered” in the regional Red List. "Alien species" were introduced by humans after the 1500s.
Geppert, Marini and colleagues classified the 1,479 analyzed plant species from the autonomous province of Trento in north-eastern Italy as common (1,507 species), rare species (604), and alien (134). The temperature increase from 1981 to 2010 (0.75 degrees Celsius) in the region leads to the expectation that a plant's range will migrate uphill by an annual average of four meters. Because the average temperature at a certain altitude is an important factor in determining whether a plant can thrive there. The average annual temperature usually decreases with every meter of altitude.
In the case of the common species, such as white clover (Trifolium repens), the lower limit of the distribution area shifted by 2.9 meters on average over the year, but the upper limit by only 2.2 meters. The distribution area thus shrank somewhat in terms of altitude. The situation was more drastic with the (potentially) endangered species, for example the summer Adonis (Adonis aestivalis): the lower limit increased by more than four meters on average, while the upper limit increased by less than half a meter. These species have therefore lost a significantly larger part of their range than the frequently occurring ones.
The development is more advantageous for non-native species, such as wild sorghum (Sorghum halepense). According to the study, these species spread up the mountains at an average of more than four meters per year, while the lower limit of the range hardly changed. Both the endangered species and the non-native species are predominantly adapted to a warm climate, while some of the endangered species are also adapted to a medium-warm climate. But the alien species have some competitive advantages, such as a high relative growth rate.
Among other things, the authors of the study advocate changing the protection strategy for endangered and endemic species, which only occur in a limited area, and shifting the focus from higher to lower areas in the Alps. "Although endemic high-mountain plants may be increasingly threatened by global warming in the future, most of them do not appear to be under immediate threat and therefore we should prioritize the lowlands to implement more urgent conservation measures," the researchers write. In lower areas, native plants are not only exposed to climate change, but also to a greater extent than species that have migrated to the highlands and also to habitat destruction by humans.
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