Population responses to on-going climate changes can consist on: (i) allocating all ressources in surviving to new stressful conditions with a gradual loss of fecundity that eventually might lead to the population extinction ; (ii) colonize new suitable areas, thus expanding their current distribution ; or (iii) undergoing some evolutionary change allowing local populations to increase their overall fitness, (i.e., local adaptation). In fact, forest populations need to combine the three types of responses to overcome external changes, and we need to consider the interplay between demo-genetic-processes (involving demographic changes with genetic consequences such as increased fecundity variance) and evolutionary responses (involving adaptive changes across generations). A sizeable proportion of Mediterranean forests are currently undergoing a demographic expansion or a displacement of their distribution area due to/in addition to climate change. In these populations, we hypothesize that the wave front of the expansion is a location where demographic and selective processes have strong and rapid effects on the evolution and structuration of genetic diversity. Our objective is to detect in genotypic data patterns indicating : (i) the role of long distance dispersal in favouring the mix of genotypes in the front wave ; (ii) demo-genetic processes in the front wave that would enhance local recruitment ; and (iii) adaptation of traits favouring survival in increasingly arid conditions. We investigate these questions by studying two populations that have successfully regenerated and expanded in the latest decades from forest remnants (J. p. turbinata) or from a single founding population (C. atlantica) and where all trees are still present. This providing the unique opportunity to study in the same environment several cohorts of trees that were born in the last hundred year, the management time-scale at which we aim to understand micro-evolution. Our project will combine three contrasted approaches (i) reconstruction of chronosequences of the expansion based on aerial pictures and field measurements that will provide information of how the expansion took place in space, time and ecological conditions (ii) landscape genetics and genomics where statistical analysis of the spatio-temporal patterns of genetic diversity (of both microsatellites and SNPs associated to resistance to drought) will inform us about the parameters of on-going demo-genetic processes and (iii) modelling the interplay between demographic and genetic factors in order to predict the fate of forest populations under different climate scenarios and for a variety of sets of demo-genetic parameters. The ExpandTree project relies on the tight collaboration between the teams of C Garcia (CIBIO, Porto) and E Klein/S Oddou-Muratorio/F Lefèvre (INRA, Avignon) and takes benefit of the comparable situations of the two study sites identified for juniperus woodland (Doñana, Spain) and Cedrus (Mont-Ventoux, France). The participants will acquire comparable data and will conduct similar analyses. This will enable the comparison of the ecology of two species that inhabit two of the most threatened Mediterranean ecosystems : semi-arid coastal dunes (J. p. turbinata) and Mediterranean mountain forest (C. atlantica).