Boreal forests, which make up roughly one‐third of the world's total forested area, provide critical ecosystem services including carbon stocks, climate‐feedbacks, permafrost‐stability, biodiversity, and economic benefits. The Siberian boreal forest is the largest continuous forest region on Earth and plays a crucial role in regulating global climate. However, the distribution and environmental processes behind this ecosystem are still not well understood. The GlacialLegacy project assessed whether summergreen and evergreen needle‐leaf forests represent alternative quasistable states that occur today under similar climatic conditions, but were triggered by different environmental conditions and gene pools during the Last Glacial. GlacialLegacy used coherent empirical and modelling approaches to investigate this hypothesis across the entire Northern Hemisphere.
Our combined pollen and sedimentary ancient DNA analyses showed that larch, a summergreen coniferous tree, was able to survive with substantial populations in northeastern Siberia, and was able to spread out of these refugia during the late Glacial period. Evergreen tree taxa, including spruce and pine only expanded during the Holocene from southern refugia. Our investigations yielded support for vegetation-permafrost interaction at the local-scale. However, our vegetation assessment did not find evidence for stable states in forest composition as a first order signal at the larger scale. In addition to permafrost, we found that fire was in a complex way connected with forest composition and human impact in Siberia during the Holocene. Our predictions also indicate that forest changes are slow and characterized by substantial lag times which is also of relevance for ongoing forest changes. Furthermore, we found that forest composition has a substantial impact on lake water quality, which is of relevance for drinking water quality particularly in the densely populated arid areas of Central Yakutia. So our results contribute substantial knowledge to the potentially critical future ecosystem service changes required for adaptation strategies to be prepared.
