Genetic variation and origin of mountain birch on a recently colonized glacial outwash plain by Vatnajökull glacier, southeast Iceland

Mountain birch ( Betula pubescens subsp. tortuosa (Ledeb.) Nyman) is the only indigenous forest-forming tree species in Iceland, and conservation of the remaining native birch forests is a recognized priority. In the last 30 years, a glacial outwash plain at Skeiðarársandur, southeast Iceland, has been colonized by birch which has now been established on an area > 35 km 2 . Genotyping by sequencing was used to determine the origin of the birch plants in the new population by assessing the genetic variation of its first generation and assessing its relatedness with the three neighboring but geographically isolated woodlands/forests closest to the outwash plain (Núpsstaðarskógar, Bæjarstaðarskógur, and Skaftafellsheiði). In total, 135K single-nucleotide polymorphisms (SNPs) were obtained, and 26K SNPs with the lower allele frequency (MAF) > 5% in 20,562 contigs. The new population on Skeiðarársandur most likely originated from Bæjarstaðarskógur and has slightly less variation than the established forests. Comparisons of the three established forests show that the adjacent forest Bæjarstaðarskógur and Skaftafellsheiði are more similar to each other than to Núpsstaðarskógar.