WASHINGTON: The acceleration of climate change is stressing mountain plants in Europe and driving them to migrate to higher altitudes, according to a study released on Thursday by US researchers.

The plant migration is also decreasing species diversity, the study's authors said in the April 20 edition of the journal Science.

The study was based on an inventory of flora on 66 mountains between northern Europe and the Mediterranean.

An increasing number of plant species was found only on mountains in northern and central Europe, the researchers reported, while in nearly all mountainous regions of the Mediterranean, the number of plant species was either stagnant or declining.

The researchers, who were coordinated by the Austrian Academy of Sciences and the University of Vienna, produced a map of plant species on each of the sites studied in 2001 and 2008.

“Our results showing a decline at the Mediterranean sites is worrying because these are the mountains with a very unique flora and a large proportion of their species occur only there and nowhere else on Earth,” said Harald Pauli, coordinator of the project.

“The observed species losses were most pronounced on the lower summits, where plants are expected to suffer earlier from water deficiency than on the snowier high peaks,” he said.

Mountainous areas at lower elevations typically experience a dry season in summer whereas at higher elevations, melting snow provides water to plants during the summer dry season.

Climate warming and decreased rainfall in the Mediterranean region in recent decades corresponds perfectly to the decrease in plant life, said Georg Grabherr, who chairs the Global Observation Research Initiative in Alpine Environments.

“In addition, most of the Mediterranean region will become even drier in coming decades,” Grabherr said.

“Impacts of climate change, either through warming or combined with increased drought stress, are likely to threaten alpine plants not only on the continent, but even on the world-wide level,” he said.