Mountain ecosystems are experiencing a major mix-up in plant species, thanks to climate change. As Earth heats up the cool alpine temperatures, plant species have begun a slow-motion diaspora to escape, relocating upward an average of 29 meters per decade. With plant species migrating at different speeds, the entire makeup of mountainside communities is changing and potentially heading toward extinction, researchers conclude online today in Science .
Previous research has shown that alpine flora and fauna are especially vulnerable when it comes to global warming and that the upper and lower boundaries of populations' home ranges have been moving higher up the mountain with every successive generation. Instead of focusing on those edges of a species range, Jonathan Lenoir, a plant ecologist at the Paris Institute of Technology in France, and colleagues decided to examine what climate change was doing to optimum ranges--the zones where most of a population lived--for plants in the mountain forests of western France. By analyzing species surveys that spanned a century, from 1905 to 2005, they were able to map the migration of 171 species.
The researchers found, overall, that the plants' ideal ranges were moving upward and doing so quickly. This upward climb matched that of the temperatures in the French mountains--which have risen, more or less, by roughly 0.6°C in the 20th century--a much more dramatic increase than that of average worldwide temperatures. Furthermore, each kind of plant shifted its optimum range at a different pace: Strictly mountain-living species such as alpine wildflowers moved faster, whereas species that were able to live in lowland areas, such as the common juniper, were less hurried. Plants with shorter life cycles--such as grasses and herbs--also climbed quickly, leaving slow-maturing trees such as the silver fir to creep behind them. Such varied migration rates mean climate change is ripping apart the delicate connections between mountainside species, the team concludes.
This spells bad news for many mountain species, says Chris Thomas, a biologist at the University of York in the U.K. "The fact that you’re getting elevation shifts is symptomatic that some species might get pushed right off the top of the mountains," Thomas says. "In some cases, that may mean localized extinctions--or it could mean complete extinction."
Georg Grabherr, a plant ecologist at the University of Vienna in Austria who specializes in alpine plants, hadn't expected the species to move so quickly over the decades. "I am somewhat surprised about the magnitude of [the plants'] shift," he says. "These are forest plants, and forests are very resistant to migration."