Genetic diversity in young and mature cohorts of cultivated and wild populations of Picea asperata Mast (Pinaceae), a spruce endemic in western China

Dragon spruce (Mast) is a conifer endemic to western China and a popular species for reforestation programs of this region. We used inter simple sequence repeats (ISSRs) molecular markers to conduct a population genetic study of nine geographically close stands from three types of dragon spruce forests: (1) intact, (2) plantation, and (3) natural regenerated following clearcut. Our main objective was to investigate the genetic structure of these populations and our expectation was that gene flow was an important evolutionary force among them. We were unable to sample a large number of individuals in each cohort. However, when young and mature cohorts from a particular stand were interpreted as a single unit, then sample size increased significantly. The highest levels of genetic diversity were found in mature cohorts of the intact forests, the lowest in young cohorts of these stands. Contrary to our expectations, low levels of gene flow existed between mature and young cohorts of different forest types; and most gene flow occurred between cohorts belonging to the same stand. There were major differences in the genetic structure of the three types of stands. Our results have conservation implications as the majority of wild populations of dragon spruce are small and fragmented. Low gene flow among populations will lead to high levels of genetic drift and a decline of genetic diversity within populations.