How climate change is slowly driving biodiversity off the mountain
Climate change is causing temperatures to rise, pushing the treelines higher up in mountain ranges. Rare species that live above that treeline are forced to seek higher ground. How did nature cope with warm periods in the past? University of Amsterdam alumna Eline Rentier is reconstructing this on a large scale for the first time.
When Eline Rentier, UvA alumna and PhD candidate at the University of Bergen, goes hiking in the mountains with friends, she is sometimes surprised that her fellow hikers see the mountain as a fixed entity. Rentier: “The mountains are constantly changing. Rivers cut into them, glaciers wear away rock, and fluctuations in temperature cause flora and fauna to move across the mountain.”
This is not surprising, as Rentier’s daily work involves researching how nature has moved across the mountain over the past 120,000 years. She does this at the Mountains in Motion research group, led by UvA alumna Suzette Flantua in Norway. She focuses specifically on alpine zones: the climate zones found only at the tops of mountains, above the tree line and below the permanent snow line.
Alpine zones are characterised by harsh conditions. It is cold, windy, the ground consists mainly of rocks and the growing season is short. Many species that live there have specialised in order to survive. Examples include the alpine marmot, the ptarmigan (snow grouse) and the famous rock plant edelweiss. When the temperature rises and the tree line seeks higher ground, alpine zones are slowly pushed off he mountain and the rare species are outcompeted by other species for whom the area then becomes habitable.
Mountain islands
In order to predict the consequences of a further rise in temperature for nature in high mountains, researchers are looking to the past. How have alpine zones moved across the mountains over the past 120,000 years? Together with her team, Rentier is mapping the location of the tree line and glaciers in the mountains of Europe, Africa, America and Asia, as well as the global temperature at that time. This is the first time that researchers have reconstructed the position of alpine zones over time on such a large scale.
Rentier is looking not only at the absolute shift in temperature, but also at the rate of change. “The last 120,000 years have been characterised by enormous fluctuations in temperature. There were very cold periods, such as the last ice age, and warmer periods between the ice ages. We are now in a warm period, glaciers are melting worldwide and the tree line has already shifted significantly upwards in the last fifty years. But that situation is not unique. The speed at which the temperature is now rising is, however, something we have not seen in the last 120,000 years.”
This is worrying because it does not give the unique species that inhabit the alpine zone time to adapt. Ultimately, this will be at the expense of the alpine biodiversity on the mountain and therefore also of the ecosystem services that nature provides, such as purifying water, clean air and generating food. In the Himalayas, researchers have already shown that the advancing tree line affects the amount of water that flows downhill.
The research is still in full swing. Rentier has now mapped the tree line, but the glacier line is still under construction. Rentier hopes to publish these results in June when she defends her PhD.
