The study of the colonization of silver fir (Abies alba) in the Pyrenees, where the species forms its southwestern distribution limit in Europe, has been widely debated based on palaeobotanical records. The debate has revolved around two main issues: 1) whether there were silver fir refugia in the Pyrenees or nearby areas during the Last Glacial Period, and 2) how the colonization (or expansion) of silver fir occurred during the Holocene in the Pyrenees._x000D_
In this study, palaeobotanical information gathered through a literature search and obtained from pollen diagrams was compared with novel genetic data from 43 silver fir populations on the southern Pyrenean slope. Additionally, these data have been compared wit

This study aims to provide a better understanding of the corelation between pollen and vegetation. There are differences in pollen productivity among different taxa that cause a non-linear relationship between pollen dispersal and vegetation data. Four elevational gradients in the Catalan Pyrenees, ranging from alpine (2750 m) to montane-basal environments (797 m), were studied. A detailed map of vegetation cover was used, and a reclassification into eight taxonomic categories that represent at least 80% of the pollen spectra was made. For each point, a moss sample (used as a pollen trap) was collected, and the percentage of vegetation cover was measured at different radii. Additionally, a detailed plant inventory was made a few meters around each point.

The pollen results showed a complete dominance of Pinus percentages, making it difficult to perceive the dynamics of other relevant taxa. In alpine environments, Poaceae is always clearly underrepresented due to the long transport of Pinus pollen. Moreover, grazing often leaves no time for plants to flower, and some species of Poaceae show changes between sexual and vegetative reproduction in response to herbivory. Additionally, there are groups within this family where cleistogamy is quite common, causing low pollen dispersion. The pollen percentages of Abies alba are highly underrepresented. It appears that a significant portion of its pollen grains settle within less than 100 meters from the sampling point. Due to the size, shape, and density of fir pollens, the decline in pollen deposition with distance from the source is remarkable. Subsequently, it can be stated that the records in the Catalan Pyrenees with high percentages of fir pollen found during the middle Holocene would indicate the presence of dense and mature fir forests nearby the coring point. Betula and Corylus populations present more unpredictable pollen percentages, probably because they act as secondary communities.

h genetic data available for the northern slope (Scotti et al., 2021). To study colonization dynamics, we analysed the beginning of the continuous silver fir pollen curves on 43 selected pollen diagrams to identify the species arrival._x000D_
No glacial refugia were either because they did not exist or because they were crypto-refugia and could not be detected. According to genetic data, there were two genetic groups in the Pyrenees that probably originate in two or more refuge zones. They have been identified eastern and western groups and a central mixed area. Paleobotanical and genetic data agree if different Holocene colonisation phases occurring during different periods are assumed. There would have been a primary colonization path from east to west during the early Holocene and additional but minor colonisations from crypto-refugia due to Holocene climatic changes.

Ramon Pérez-Obiol¹, Anna Badia², Marc Sánchez-Morales^3, Jordi Nadal²

^{1 Department of Animal Biology, Plant Biology and Ecology, Universitat Autònoma de Barcelona, Spain}

^{2 Department of Geography, Universitat Autònoma de Barcelona, Spain}

^{3 Department of Biosciences, Universitat de Vic-Universitat Central de Catalunya, Vic, Barcelona, 08500, Spain}

ID Abstract: A12