Taiga could displace Siberian tundra almost completely | Polarjournal

The tundra is a vegetation zone that extends beyond the tree line in the northern hemisphere from about 55° north in Canada to 80° north in Svalbard. The predominant plant community is inconspicuous at first glance, but surprisingly diverse, ranging from mosses and lichens to grasses, bellflowers, buttercups, and saxifrage to dwarf shrubs such as dwarf birch and polar willow. At the Arctic tree line only single trees can be found like here at Lake Keperveem (Russia, Chukchi Autonomous Okrug). Photo: Stefan Kruse

The tundra in Siberia is one of the habitats already feeling the effects of climate change most severely, especially through thawing permafrost soils and changing precipitation patterns. But rapidly rising temperatures in the Arctic are also preparing the ground for the northward expansion of boreal forests, which will displace the tundra. Scientists from the Alfred Wegener Institute have now found in a modeling study that even with ambitious greenhouse gas reduction measures, only one-third of the Siberian tundra would be preserved.

In the last 50 years, the air temperature in the Arctic has already risen by more than two degrees Celsius – much more than anywhere else in the world. With a drastic reduction in greenhouse gas emissions (emissions scenario RCP 2.6), further warming of the Arctic could be limited to just below two degrees Celsius by the end of the century. By contrast, if we do not reduce our emissions (RCP 8.5), the Arctic could experience average summer temperatures 14 degrees Celsius higher than today by 2100.

Cotton grasses and the other tundra plants are well adapted to the harsh conditions with short summers and long winters. Animals such as reindeer, lemmings and insects such as the Arctic bumblebee have also found their habitat here. Photo: Stefan Kruse

“For the Arctic Ocean and sea ice, current and future warming will have significant consequences,” says Prof. Dr. Ulrike Herzschuh, head of the Polar Terrestrial Environmental Systems Section at AWI and co-author of the study. “But the environment will also change drastically on land. The vast Arctic tundra areas in Siberia and North America will decline massively because the tree line is currently shifting slowly northward and will shift very rapidly in the near future. In the worst case, the tundra will almost completely disappear by the middle of the millennium. In our study, we simulated this process in the model for the Siberian tundra in northeastern Russia. The focus was on one question in particular: what emissions path must humanity follow to save at least parts of the tundra as a refuge for animals and plants, as well as for the culture and traditional environmental relationships of indigenous peoples?”

The video shows the development of forest cover and tundra area in 10-year steps for the different emission scenarios up to the year 3000. The diagrams on the left and right of the maps show the decrease in tundra area. Video: Stefan Kruse & Ulrike Herzschuh 2022

The two authors of the study, Prof. Ulrike Herzschuh and Dr. Stefan Kruse, used the AWI vegetation model LAVESI for their simulation. “What’s special about LAVESI is that we can represent the entire tree line at the level of individuals, individual trees,” Kruse explains. “The model maps the complete life cycle of Siberian larches at the transition to tundra – from seed production and seed dispersal to germination and full growth of the tree. This allows us to very realistically calculate the advance of the tree line in an increasingly warmer climate.”

Their results show that the larch forest is expanding northward at a rate of 30 kilometers per decade. Since the tundra has no possibility of spreading because of the adjacent Arctic Ocean in northern Siberia, these areas will shrink. Forest expansion is still proceeding very slowly, as vegetation lags strongly behind warming. However, according to the simulation, the speed of spread increases sharply already from 2030. By 2500, only 5.7 percent of the tundra area in Siberia could be left. However, even under the RCP 2.6 scenario, only one-third of the original area would be preserved – on the Taymir Peninsula and in Chukotka.

Aerial view of open larch forests on Taimyr Peninsula – around Chatanga River. The larches grow here sometimes more densely, sometimes only very sporadically. Researchers refer to this zone as the tree-border region, which ranges from somewhat denser forests in the south to the north, where trees are very sporadic. Photo: Stefan Kruse

“For the Siberian tundra, it is now a matter of mere survival,” comments Eva Klebelsberg, Arctic regions officer at WWF Germany, on the study. “Only with very ambitious climate protection goals is it still possible to save larger areas. And even then, in the best case, only two refuges with smaller animal and plant populations that are very vulnerable to disruptive influences will remain in the long term. That is why it is important to expand protective measures and protected areas in the affected areas now in order to preserve refuges for the unique biodiversity of the tundra,” demands Eva Klebelsberg, who is campaigning for the designation of protected areas in cooperation with the Alfred Wegener Institute. “Because what’s clear is that if we keep doing business as usual, this ecosystem is going to disappear in the long run.”

Julia Hager, PolarJournal / Original text: Press release AWI

Link to the study: Stefan Kruse, Ulrike Herzschuh (2022): Regional opportunities for tundra conservation in the next 1000 years. eLife 11:e75163. DOI: 10.7554/eLife.75163

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