Investigation of the recent recolonisation of Beech on Mont Ventoux using historical records, vegetation analyses from satellite image and landscape genetics

In this study, we investigated the genetic structure and the recolonisation process of the European beech (Fagus sylvatica) over the north face of the Mont Ventoux Mountain, using of combination of historical record investigation, vegetation mapping from satellite image and unsupervised classification process, and a landscape genetic approach. Mont Ventoux has undergone large deforestation phases until the XIXth century due to over-grazing and over-logging for woof supply. Historical records showed that the relic Beech populations were distributed as small but not isolated forest fragments on a belt at around 1300 m in elevation. Vegetation classification based on satellite images allowed to map with a correct accuracy the present distribution of Beech on North face of Mont Ventoux, and confirmed its presence almost everywhere between 950m and 1500 m in elevation. Finally, we used the landscape genetic approach implemented in Geneland software in order to identify the delimitation of population units and to correlate the genetic discontinuities to landscape features. Over 38 experimental plots, we sampled 1599 individuals divided in two cohorts (young beech stands and relic-trees), and genotyped them at 13 microsatellite loci. Standard population genetic analyses showed small but significant genetic differentiation among experimental plots (Fst = 2.57%). Moreover no significant pattern of isolation by distance among plots was found. However the GeneLand model success to identified 3 main clusters and 2 marginal populations. No obvious correlation were found between the genetic discontinuities and the topography or the landscapes features. These results concerning the past response of Beech to a major population decline suggest that beech population of the north face of the Mont Ventoux are able to resist to quite high level of disturbance without major impact on their genetic structure