Global warming is threatening ecosystems and vegetation zones around the world. But in the far north, climate change is progressing particularly quickly and is replacing the Siberian tundra with the spread of coniferous forests. A simulation now shows that if no climate protection measures are taken, the Siberian tundra could almost completely disappear by the middle of the millennium.
The Siberian tundra is a vegetation zone between the frozen landscapes of the Arctic and the boreal coniferous forest. In this region, the ground is almost completely frozen, so that no trees grow in this cold steppe, only a few specially adapted plants. In the course of evolution, the harsh conditions produced special plant species, some of which are found exclusively in the tundra and the arctic. This habitat is also home to unique animals such as reindeer, lemmings or the arctic bumblebee.
However, climate change does not stop at the arctic tundra either, in fact, it hits particularly hard there. The average air temperature in the far north has risen by more than two degrees Celsius in the last 50 years – and thus much more than in other regions of the world. The rise in temperature causes the tundra soils to thaw more frequently and quickly in summer. As a result, the tree line of the Siberian forests bordering to the south is shifting further and further north. This displacement of the vast areas of the cold steppe with its unique flora and fauna could continue in the coming years.
Simulation sees Tundra in distress
In order to find out how badly the Siberian tundra is actually threatened, Stefan Kruse and Ulrike Herzschuh from the Alfred Wegener Institute for Polar and Marine Research in Potsdam simulated the future spread of forests at the expense of the tundra on the computer. To do this, they use the LAVESI vegetation model, which can even represent the position of the Arctic tree line at the level of individual trees: “The model maps the complete life cycle of Siberian larches at the transition to tundra – from seed production and seed dispersal to germination for full growth of the tree. In this way, we can very realistically calculate the advance of the tree line in an ever warmer climate,” explains Kruse.
The results of the simulation show an alarmingly rapid displacement of the treeless cold steppe: According to the calculations, the larch forest will spread northwards from Russia at a rate of 30 kilometers per decade. The tundra areas, which cannot shift to colder regions because of the adjacent Arctic Ocean, are shrinking more and more as a result. The spread of forests follows warming at some distance, since the trees with their seeds only have a limited propagation radius. At some point, however, the trees will inevitably catch up.
Climate protection can mitigate the consequences
According to the forecasts, the tundra in Siberia could shrink so much that by the year 2500 only about six percent of today’s tundra area would be left. “In the worst case, the tundra will disappear almost completely by the middle of the millennium,” predicts Herzschuh. However, since this model was developed for a scenario without any climate protection, there is still hope for the icy vegetation zone, according to the two researchers: “Ambitious strategies to mitigate global warming could prevent such an extreme loss and preserve around 32.7 percent of today’s tundra “. According to the simulation, what used to be 4,000 kilometers of continuous tundra belt in Siberia will then have shrunk to two areas that are 2,500 kilometers apart.
In this scenario, however, the diversity of plant and animal species of the tundra would be severely threatened, as geographic isolation results in smaller populations that are less able to respond to environmental changes and disturbances. “It is therefore important to expand protective measures and protected areas in the affected areas in order to preserve retreat areas for the unique biodiversity of the tundra,” demands Kleberlsberg from the nature conservation organization WWF, who was not involved in the study. Because thanks to the simulation, it is now certain that this ecosystem will disappear in the long term without measures to curb global warming.
Source: Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, Article: Ecology, doi: 10.7554/eLife.75163