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Genetic characterisation of a global climate change-induced altitudinal tree-line shift in European beech (Fagus sylvatica)

Final Activity Report Summary - FOREST RISE (Genetic characterisation of a global climate change-induced altitudinal tree-line shift in European beech (Fagus sylvatica))

This project represents a novel approach to the study of the response of plants to climatic variability. It combines molecular genetic analysis of natural populations with dendrochronological (tree-ring) and climate data to allow investigation of climate as a driving force in changes in adaptive genetic change in natural populations. The work was based in the Montseny mountains of Catalonia (NE Spain), where a recent increase in the altitude of the mountain tree line has been reported. This tree line shift is evidence of changes plant distribution that are resulting from global warming and recent changes in land use.

Using a genetic fingerprinting technique ('AFLP') we compared the genetic structure of European beech (Fagus sylvatica) trees at the upper and lower limit of the species distribution and in a central area of the beech forest in the Montseny mountains. We used state-of-the-art statistical procedures (population genomic methods) to identify a region of the total beech DNA (the beech genome) that was being selected for at the upper treeline, and selected against at the lower limit of the species distribution.

For each tree we also calculated the year in which that individual established. We analysed this establishment data alongside the data of presence or absence of the DNA region under selection (as described above) and mean annual temperature data. This enabled us to identify patterns of genetic change that are occurring over space (with increasing altitude), with increasing temperature, and over time as a consequence of recent increases in temperature due to global warming.

The most important scientific achievement from this project is the identification of genetic variation for temperature response within the natural population of this species. Genetic change is occurring over time in response to increasing temperatures, this shows that this species possesses a limited potential to adapt to changing temperatures within current populations.

This project successfully met all of the principal project objectives set out in the original proposal document, thereby demonstrating that the initial planning was sound and that the project ran according to plan. Specifically these objectives were as follows:

Objective 1. To determine whether juvenile subpopulations of beech trees established at the upper and lower altitudinal margins (respectively, the advancing and retreating edge of the migration) of the temperate forest zone exhibit lower levels of genetic diversity than a similar sample of more central trees. There was no evidence of reduced diversity at either the advancing or retreating range edge when compared to the central area of the forest.

Objective 2. To determine the degree of climatic segregation of beech subpopulations in the central region of the temperate beech zone and the primary climatic variables responsible - i.e. trees preferentially establishing in warm v cool or dry v wet years. 'Genetic segregation was detected in response to temperature (as outlined above) not in response to precipitation. This genetic segregation affects a specific region of the beech genome' thereby indicating a region likely to contain a gene or genes selected for by hot or cold temperatures during plant establishment.

Objective 3. To assess the extent to which the documented altitudinal migration of beech in the Montseney Mountains has led to the spatial segregation of these subpopulations. These subpopulations are segregated both spatially and temporally as a result of temperature variation within the forest. For example, the number of individuals possessing the selected DNA region increases with altitude and decreases over time as the climate warms, thereby demonstrating that climate change is driving genetic change in the population.