The warmer climate in the Arctic tundra is changing the species composition, as shown by a study involving the SLF, WSL and the University of Zurich.
Up until now, the only plants to grow in the Arctic were low-growing grasses and dwarf shrubs. To withstand the harsh environmental conditions, they stay close to the ground and are often only a few centimetres high. However, this is changing with climate warming: over the last 30 years, communities of plants that grow significantly higher have emerged in the tundra, as shown by a study by 130 international scientists, including researchers from WSL, the SLF and the University of Zurich. The study has just been published in the renowned journal Nature.
As part of the study, the researchers analysed the most extensive data set yet on plants in the Arctic tundra, comprising observations at around 120 points in the Arctic Circle, including Alaska, Canada, Iceland, Scandinavia and Siberia, as well as at higher altitudes in the Alps, where the climatic conditions are very similar to those in the Arctic.
The data show that the increase in height has taken place not just regionally but at almost all locations studied. Some of the traditional plant species are now growing taller than they did 30 years ago but the biggest change is that higher-growing plant species that normally grow in warmer regions have spread throughout the tundra.
A similar phenomenon can also be observed on the Alpine peaks, as revealed in an earlier study by SLF and WSL researchers, which was published in Nature. "Plant species from lower altitudes are spreading to higher altitudes due to climate warming," says Christian Rixen, a mountain ecologist at the SLF.
The change in plant communities in the tundra can also be attributed to climate warming. Over the last 30 years, temperatures have risen by an average of around 1 oC in summer and 1.5 oC in winter in the locations studied. As a result, the Arctic is warming up faster than almost anywhere else on earth.
The trend towards higher-growing plants is still far from over: according to the researchers' estimates, the height of plant communities in the tundra could increase again by an average of about 20 to 60% by the end of the century. Furthermore, the study shows that the changes are not only dependent on temperature increases but also on other factors, in particular soil moisture. Because of the low temperatures, there is still very little precipitation in the tundra. "Based on our results, we expect greatly accelerated vegetation growth in locations where precipitation sharply increases as well," says study co-author Gabriela Schaepman-Strub from the University of Zurich.
One possible effect of higher-growing plant communities could be that more snow will accumulate around the plants in winter, insulating the soil. The active layer of the permafost will therefore no longer freeze as quickly. Up to half of the carbon stored in soil worldwide is found in permafrost. If it thaws, large amounts of CO2 and methane could be released, which would further accelerate climate warming.
Scientists from various institutions, such as the Senckenberg Biodiversity and Climate Research Centre (BIK-F), the German Centre for Integrative Biodiversity Research (iDiv), the University of Edinburgh, the University of Aarhus, the University of Zurich, the Swiss Federal Institute of Aquatic Science and Technology (Eawag), WSL and the SLF, took part in the study, which was led by Dr Anne Bjorkman. The results are based on over 50,000 individual plant measurements taken over a period of 30 years to study how tundra ecosystems are reacting to climate warming.