History of the European larch (<em>Larix decidua</em> Mill.)

Abstract

This thesis focuses on the consequences of past climate and anthropogenic changes on populations of the European larch (<em>Larix decidua</em> Mill.) by integrating palaeoecological and genetic data. Such retrospective approaches provide a useful context for evaluating possible impacts of ongoing changes. A limitation of current studies dealing with forest trees is that they often deal exclusively with postglacial recolonization. Effects of more rapid changes on forests, including those caused by recent plantations or by abrupt climatic events of the last glacial, have been largely neglected. In this study high resolution genetic data and precise vegetation records correlated with high-resolution climate records of the last interglacial/glacial cycle (130,000 years) were used to precisely document long-term and short-term events that impacted the history of European larch. For the genetic analysis, highly informative nuclear markers (microsatellites) were designed and applied on a range-wide sample of 45 modern larch populations. These data were analysed together with mitochondrial data to establish a baseline for studies focussing on recent translocations. Results revealed that larch has been planted extensively, generating admixture between native and non-native populations from multiple sources across the range. Translocation events and admixture rates were distributed unevenly across the range, with a particularly high frequency in Poland, Slovakia and the Czech Republic where larch has a more scattered distribution compared to the Alps. Some of the most valuable populations appear to be seriously endangered by translocations. The palaeoecological results showed that larch persisted close to its modern distribution throughout the last interglacial/glacial cycle but that its range was highly dynamic and in equilibrium with both long-term and short-tem climate events, in line with the pioneer character of the species. The extent of species distribution was maximal during the first early Weichselian interstadial when larch built boreal forests in the north-central European lowlands (87,000 – 109,000 years ago). Responses to short-term climate events (Dansgaard-Oeschger cycles, Heinrich Events) were extremely rapid. Seven Last Glacial Maximum (LGM) refuges were detected using fossils and genetic data. This made it possible to identify recolonization pathways and concomitant introgression and homogenisation, highlighting the power of the joint population genetic and palaeoecological perspective.