Trees and shrubs are likely to be most threatened by rising temperatures
Climate change has caused plants to seek cooler conditions at higher altitudes, scientists suggest.
A study of 171 forest species in mountain ranges of western Europe found that many plants had climbed an average of 29 metres each decade.
Smaller species such as ferns, which had shorter reproduction cycles, were the quickest to relocate, the researchers said.
The findings have been published in the Science journal.
"This is the first time that it has been shown that climate change has already had a significant effect on plant species over a wide range of temperatures during the past century," explained Jonathan Lenoir, the paper's lead author.
Professor Lenoir, an ecologist at AgroParisTech, France, said the team wanted to establish whether "fingerprints of climate change were already apparent in ordinary ecosystems".
In order to do this, the team of French and Chilean researchers compared the distribution of forest species between 1905 and 1985 with their distribution between 1986 and 2005.
"This work was possible because of two large-scale, long-term databases that have recorded the presence of forest species since 1905," he explained.
This may imply profound changes in the composition and structure of plant communities and animal species that depend upon them
Professor Jean-Claude Gegout,
"We used 171 species commonly found over French mountains, which are part of Mediterranean, temperature and mountainous forest ecosystems between 0m to 2,600m above sea level.
"We found a significant change in species' altitudinal distribution towards higher elevation of about 29 metres per decade.
"Out of the 171 species, most are shifting upwards to recover temperature conditions that are optimal for their development and reproduction."
Co-author Jean-Claude Gegout added that different types of plants displayed different responses to the temperature changes.
"Long-life plants, such as trees and shrubs, did not show significant shifts, whereas short-life species, such as herbs, showed a strong upward shift," he said.
"Herbs, by having a short life cycle, have had several generations during a decade that allows for a faster dispersal of seeds.
"By contrast, trees have had just one or two generations during the same period of time, which may affect their ability to track the climate changes."
Professor Gegout said that this suggested that long living woody plant species, such as trees, were likely to be more threatened by climate change than herb species like grasses.
"This may imply profound changes in the composition and structure of plant communities and animal species that depend upon them."
The researchers concluded by saying that further studies were needed to understand the full magnitude of the changes, and to assess the impact on the ecosystems' long-term future.