Abstract: Understanding the past and future evolutionary dynamics of dominant species in a forest is important for guiding decisions for biodiversity conservation, forest management, and vegetation restoration. This study used Quercus schottkyana, a dominant tree in subtropical evergreen broad-leaved forests in southwest China, to investigate the influences of past environmental fluctuations and future changes in climate on the dynamics of tree demographics. Genomic data were obtained for 133 samples of Q. schottkyana from 22 populations using double-digest genotyping by sequencing. The single-nucleotide polymorphisms in the genome showed a uniform distribution. Based on principal component analysis and Admixture analysis, two distinct lineages and one mixed group were identified that corresponded to their geographical distribution. Approximate Bayesian computation analyses provided evidence that the divergence among Q. schottkyana populations could be driven by the collision between the Asian and Indian plates during the Miocene, and that climatic fluctuations in the late Pleistocene led to the introgression. The analysis of genotype-environment relationships showed that annual precipitation and geographic distance were associated with spatial genetic variation. Populations of Q. schottkyana in the northern area of the Jinsha River basin were predicted to be the most vulnerable to future climate change. To increase genetic diversity in the northern Jinsha River basin and to buffer threats from future climate change, managers could use a mixture of local and alien seeds during forest restoration and management. This case study can promote further investigations into assessing how past and future climate change impacts genetic divergence and local adaptation of trees in forests.

Key words: climate change, demographic history, forest dynamics, genomic vulnerability, landscape genomics, Quercus