Figure 1. Locations of the study sites.

The 13 study sites selected represent four different biomes: boreonemoral, southern boreal, northern boreal and subarctic-arctic vegetation zones. Fossil pollen and macrofossil study sites are indicated with numbered circles. (1) Lielais Svetinu, (2) Nakri, (3) Kankaanjärvi, (4) Laihalampi, (5) Kråkenes Lake, (6) Loitsana, (7) Kipojärvi, (8) Njargajavri, (9) Korsajavri, (10) Jansvatnet, (11) Llet-Ti, (12) Tumbulovaty and (13) Kharinei. See Supplementary Table 1 for details and references about these sites. The study site locations with pollen data adopted from the literature, Lake Tsuolbma16 and Toskal67, are indicated by capital letter A. The pollen–climate calibration data sets were selected from the 583-sample surface-pollen data set of Salonen et al.59, marked with small circles. To represent the modern pollen–climate relationships in the continentality regimes of different fossil sites, three different subsets (A: low continentality, B: intermediate continentality, C: high continentality) were selected from all the surface pollen assemblages. The modern T_jul gradient varies from 17.7 °C (Latvia) to 7.5 °C (northern Fennoscandia) and the annual precipitation varies between 1,280 mm (west coast of Norway) and 500 mm (Finnish Lapland). The elevation range of the sites is 38–705 m.a.s.l.