Higher temperatures could lead plants living at the top of Europe’s mountains to decline and disappear, as they face greater competition with plants from warmer, lower levels. That’s one finding from surveys of 17 mountain areas conducted by 17 different research teams, co-ordinated by Harald Pauli from the University of Vienna and Austrian Academy of Sciences. Comparing surveys performed in 2008 and 2001 shows that changes are already happening across the continent, and faster than the scientists might have thought. “Alpine vegetation often is given as an example of a highly resilient ecosystem, with slow-growing but long-lived plants that may not see dramatic changes over decades,” Pauli said. “Based on previous studies, we did expect that species composition will change, but not that we would get a significant signal after just 7 years.”
The idea to perform regular surveys to collect long-term measurements on what climate change is doing to mountain plants came during the 1990s, when such studies were still rare. Pauli and his colleagues were comparing modern species numbers in mountains with those measured by botanists 50-100 or more years earlier. They found more species than had been previously able to live there, but data were patchy and limited to the Alps and Scandinavia. “This obvious scarcity of comparable data from permanent plots across many mountain systems led to the establishment of the GLORIA network around the turn of the century,” Pauli said.
For a paper published in Nature Climate Change last week, 32 GLORIA scientists from 13 countries used the same methods to study 867 vegetation samples from 60 different mountain tops. The group was divided into teams based near the mountain range they studied, meaning they had the best knowledge of the local plants. Their methods relied on visually estimating how much of the area of marked-out and temperature-monitored plots on each mountain is covered by each different type of plant. “The basic unit is a 1 x 1 m square plot – four such plots are arranged in each compass point of each summit site, making 16 such plots per summit,” Pauli explained. “The distribution of the plots over all main compass directions should result in a maximum coverage of vegetation types that occur on a summit site.”
A stronger signal than expected
After repeating the same surveys in 2001 and 2008, the reseachers compared the results against minimum June temperature at the plots. They found that alpine plants, which are ground-hugging, light-hungry, adapted to cold temperatures and slow to grow, face more competition as the world warms. While changes across different mountains varied, when taking Europe as a whole there were strong indications that such plants are being squeezed out.
“Alpine vegetation across Europe experienced a so called ‘thermophilisation’,” Pauli said. “In other words, more warm-demanding species that usually dwell at lower elevations now occur higher than seven years ago. The proportion of warm-demanding species either increased by invasion of new species or by an expansion of already occurring species. The magnitude of change was related to an increase in the minimum June temperature. A period of 5 to 10 years is very short for detecting changes in species cover. We were surprised to see a significant signal.”
For some species extinction will therefore become unavoidable “within the next few decades, if this is not already the case”, Pauli said. Other alpine species will see a reduction in the richness of genetic information in their population, he assumes, while some of the warm-demanding species will increase. In fact, identifying which will succeed and which will suffer are just some of the questions that Pauli wants answers to. “What effect does warming have combined with decreasing precipitation, as we currently observe in parts of southern Europe?” he asks. “How does this compare with changes in other continents?” he inquires. The answers may now be elusive, but the GLORIA team have a well-defined plan of action to find them. At the core of that plan? The next return to the surveying plots on these 60 mountains.