Response of Siberian treeline forests to historical and present climate changes - a (paleo)genetic approach

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The circum-arctic boreal treeline is projected to move further north in response to the prospected strong high-latitude warming. This process will potentially have tremendous effects on climate - due to changes in vegetation-climate feedbacks - and on biodiversity. The reduction of tundra ecosystems and the increase of forested areas will lead to significant changes in biodiversity, both at the level of species and of intraspecific genotypes. To date, the treeline changes are not sufficiently documented or understood, especially in Siberia, where about half of the global circum-arctic boreal treeline is located and dominated by larch (Larix). It is uncertain (A) how fast Larix forest can colonize new areas (migration speed), (B) which are the spatial patterns of recruitment and spread (migration pattern), and (C) how competition between Larix species and genotypes affects larch forests in times of climatic change (competition effects). To address these questions this project proposes a multidisciplinary program to study arctic treeline dynamics at the decadal scale (within the last 400 years) and throughout the Holocene in North-Eastern Siberia. The arctic-boreal treeline has experienced multiple periods of treeline fluctuations during the Holocene, and these will be analysed. The project combines the use of palynological and dendrochronological investigations with sedimentary ancient DNA analyses. The use of sedimentary ancient DNA has to date mostly been restricted to species identification, but genetic data can also potentially be used to address temporal dynamics within single species. In this project, lake sediment cores from the southern Taymyr peninsula will be analyzed. In particular, the following research objectives will be pursued: 1) Migration speed: The occurrence of Larix will be determined using palynological and genetic data to infer the position of the treeline and determine the speed of response to climatic changes. 2) Migration pattern: Intraspecific genotypes of colonizing treeline populations will be determined in times of treeline advance, and compared to the current genotype distribution, to analyze whether recruitment is local or by long distance dispersal. 3) Competition effects: Possible shifts in the occurrence of Larix species and genotypes after forestation will be determined to analyze whether inter- and intraspecific competition influences forest composition. The analysis of these historical processes at a subspecific resolution will improve our understanding of treeline shifts and associated diversity changes, and will enable better projections of future shifts.