The East European forest-steppe ecotone crossing Europe from the Carpathian to the Ural Mountains represents one of the most important cultivation areas in the world. Modern climate change triggers increased droughts causing harvest losses, already affecting the social, economic and political life of millions of people. For a sustainable management strategy, the natural climate variability and the resilience of this extraordinary zone must be considered. The main goal of the project was to reconstruct the long-term response of the European forest-steppe ecotone to climatic changes, fire and human impact.

The selected study area between the Dnepr and the Don Rivers is situated in the heart of the East European forest-steppe. Its vegetation composition is very sensitive to changes in temperature, precipitation and human impact, while human influence is evidenced by various archaeological cultures of nomads and peasants. Palynological archives covering the last 14,800 years have been collected along a latitudinal gradient crossing the whole ecotone from the adjacent forests in the north to the steppes in the south. Multi-proxy studies including pollen, non-pollen palynomorphs, micro- and macrocharcoals, loss-on-ignition and macroremains analysis have been conducted.

The obtained data revealed that the vegetation of the East European forest-steppe is highly sensitive to moisture availability caused by the northern hemispheric climate changes. The stadial periods of the Late Glacial caused the steppe spread, while forest-steppe was developing during the interstadials. The spread of birch forest into the steppe followed the Holocene warming ~11,700 years BP when milder climate conditions allowed the development of forests all over the East European Plain. During the Younger Dryas and early Holocene, the ecosystems were affected by forest fires, but in the Middle Holocene their role had decreased. At ~10,300 years BP, the vegetation became dominated by pine. Around 8,600 years BP the forest-steppe was represented by pine-broadleaf mixed forests with Quercus, Tilia, Ulmus and Corylus. The strong spread of the broadleaf trees started ~7,000 years ago coincided with decreasing summer insolation and temperatures in the late Middle Holocene, lowering evapotranspiration and increasing the amount of available moisture. Around ~4200 years ago, the region became entirely forested including its southern limits. The southern treeline is extremely sensitive to human activities and has been largely defined by those over the past ~3500 years. With the development and spread of agriculture, local societies induced deforestation and fires to clear the land. In the last 800 years, the area of the ecotone has become deforested, reaching the minimum forest cover in the 17th century. Without constant anthropogenic pressure, climatic conditions would have allowed a wider distribution of forests during the past 2000 years. The conversion of the forest-steppe into an agrarian land allowed only very small patches of semi-natural vegetation to remain today.

Considering the current global warming, the southern tree line is likely to shift northwards, bringing the area to the mid-Holocene conditions with the dominance of steppe. The protection of forests will be necessary to maintain the heterogeneity of the forest-steppe. Lower moisture availability will increase the risks of droughts affecting agriculture in the region. Without the protection of a natural vegetation, the extensive crop lands are at risk of desertification. Urgent action is needed to protect the East European forest-steppe from the increasing effects of climate change.