Understanding rates of migration and resilience to climate change is important for explaining both the distribution of single species and anticipate how ecosystems may respond to climate change. There are two vigorously debated questions about the response of NW European biota to past climate changes: 1) glacial survival vs tabula rasa and 2) Reid´s paradox of rapid plant migration through seed dispersal vs. survival in cryptic refugia just south or east of the ice sheet. These are related as survival in any northern refugia would suggest local dispersal rather than the rapid dispersal rates that are needed from southern refugia. Our main goal was to revisit glacial survival and postglacial dispersal using metabarcoding and innovative ancient DNA methods, ultimately unifying phylogeography with palaeoecology. Our objectives were to: 1) determine whether boreal trees, dwarf shrubs, and arctic herbs survived the glaciation in glacial or cryptic refugia; 2) determine dispersal routes and calculate migration rates based on palaeo-phylogeography, and 3) model future species distributions and genetic diversity based on past dispersal rates and genetic patterns.
Our results did not provide unequivocal support for glacial survival of conifer trees in N Norway, but we have strong support that high-arctic herbs did survive locally (Alsos et al. 2020). Similar, we found high-arctic species in the oldest sediments in Iceland (12 ka, Alsos et al. 2021), N Norway (16 ka, Alsos et al. 2022) and just outside the British-Irish Ice Sheet in Wales (19 ka, Zetter 2024), suggesting glacial survival of high-arctic species in northern refugia (summarised in Brochmann et al. 2025).
In northern Fennoscandia, we detected large time lags in first appearance of plants to the region, and also the dispersal within the region was slow (Alsos et al. 2022; Rijal et al. 2021, 2025). Further, we could show how the development of the vegetation relates to local glaciation (Elliott et al. 2023) and climate changes (Rijal et al. 2021, Alsos et al 2022, Elliott et al. 2023 Salonen et al. 2024, Rijal et al. 2025). These time lags need to be taken into account when attempting to forecast future species distribution and ecosystems.
We had a breakthrough in metabarcoding of mammal DNA, which allowed us to further disentangle different drivers of vegetation changes. Using this approach, we show that grazing by domestic mammals in general increase plant diversity in the Alps (Garcés-Pastor et al. 2022, 2025), Pyrenees (Julián-Posada et al. 2025), and Carpathian’s (Magyari et al submitted), whereas similar effect of native herbivores were not detected in Northern Fennoscandia (Alsos et al. submitted) or the Polar Urals (Topstad et al in prep, Lammers et al. in prep).
To trace within-species dispersal routes, we developed a multiplexing method for the ecologically important dwarf shrub bog bilberry. To our surprise, the boreal linage arrived in the northernmost part of Norway before the arctic lineage (Lammers et al. 2024). We are currently finalising a larger dataset that will allow us to identify dispersal patterns in more details by including samples from throughout Europe (Lammers et al. in prep).
The high taxonomic, spatial and temporal resolution of sedimentary ancient DNA data is ideal for improving predictions and trajectories of future species and ecosystems. We have outlined how this can be achieved (Alsos et al. 2024) and tested some promising approaches on our dataset from ten lakes in northern Fennoscandia (Beaulieu et al, submitted). We are further exploring how our within-species level data of bog bilberry can be used to also forecast genetic diversity under future climate scenarios.
