Ancient DNA reveals how Arctic plants shifted dramatically after ice ages

Sedimentary ancient DNA (sedaDNA) has improved our understanding of past vegetation dynamics by capturing fine-scale plant community changes in response to climate and environment. Multi-lake studies often reveal substantial heterogeneity, but it remains unclear whether lakes in close proximity to each other, with similar geological histories, produce consistent reconstructions of regional vegetation trends. Here we analyse sedaDNA from Lake Maloye Shchuchye (287 m a.s.l.) in the middle of the Polar Ural and directly compare its plant taxonomic diversity and growth-form composition since the Last Glacial Maximum (LGM) with a previously examined record from the adjacent Lake Bolshoye Shchuchye (187 m a.s.l.) that we now have re-analyzed. The records reveal four statistically significant vegetation shifts, resulting in five CONISS zones over the past 24,000 years. Especially at the initiation of Bølling-Allerød and at the entry of the Holocene, the vegetation of both localities shifted considerably. These shifts were most pronounced at 14.1 and 11.4 cal ka BP in both datasets. Samples dating back to the LGM maintained a high and fluctuating inventory of taxa, many of which persist throughout the full study period. Boreal taxa appeared slightly earlier in the record from Bolshoye Shchuchye where the local climate is slightly warmer than around Maloye Shchuchye. Differences in overall richness trends were minor and predominantly driven by forb taxa, whereas trees, shrubs, and dwarf shrubs showed comparable trajectories in both lakes. Both sites were forested for several millennia during the early to mid-Holocene. There also appears to have been a persistent presence of arctic-alpine species at both sites, which substantiates the hypothesis that the Polar Ural served as a long-term refugium for arctic-alpine plants during both warm and cold periods. These results demonstrate that the sedaDNA records from the two nearby lakes, which have separate catchments, yield highly congruent vegetation histories. Together, these catchments cover large areas of the northern Polar Urals and demonstrate regional vegetation dynamics and effects of climate change. Furthermore, their congruency strengthens confidence in sedaDNA reconstructions as tools for capturing broad-scale vegetation trends while also highlighting the ecological processes underlying long term plant survival in mountain environments. • Congruent vegetation reconstructions from two separate lake catchments. • Polar Urals forested for several thousand years during the Holocene. • Major vegetation shifts align with Bølling-Allerød and the onset of the Holocene.