2 Material and Methods
2.1 Study genus
Larix Mill. is the most abundant genus in boreal coniferous forests of Eurasia and Larix species cover 70% of the forest biome globally (Abaimov 2010). Larches are well adapted to the harsh climate conditions, that is, cold winters to below −40 °C and short summers with only 60–90 days exceeding the freezing point (Franz 1973). According to different taxonomic systems, there are different opinions regarding the number of larch species and the boundaries of their habitants (Mayr 1906; Dylis 1961; Bobrov 1972). The distribution areas of some Larix species overlap and larches can hybridize easily in natural habitats (Semerikov et al. 2007; Abaimov 2010). This especially applies to the Siberian larch species. For this study, following Bobrov (1972), we recognize three species of Larix across their Siberian distribution from east to west, L. sibirica Ledeb., L. gmelinii (Rupr.) Rupr., and L. cajanderi Mayr, although we acknowledge there might be considerable hybridization between the several species and varieties. The natural distribution of Siberian larch species extends from west to east in large, relatively discrete ranges with hybridization occurring in the boundary zones (Abaimov 2010).
2.2 Study area and sample collection
The study area includes arctic and subarctic areas located in the forest-tundra transition zone in Siberia. The sites are located in Siberia from the Ural Mountains in the West, followed by the Taymyr Peninsula, to the Lena Delta and the Verkhoyansk Range reaching to Chukotka in the Far East; as well as Kamchatka in the southeast, via Magadan and southern Yakutsk to the Altai Mountains (c. 50–80°N; 50–180°E).
For genetic analyses, fresh needles from natural populations ofLarix sibirica , L. gmelinii , and L. cajanderi were taken during summer fieldwork (2011–2021) (Fig. 1). Samples were selected to cover a wide distribution area of Siberia. Needle samples were dried on silica gel during fieldwork and stored at 4°C. In total, 148 individuals were processed for which the identifier, geographic position, and height were recorded (Appendix S1).