Understanding genetic diversity of relict forests. Linking long-term isolation legacies and current habitat fragmentation in Abies pinsapo Boiss

Increasing variability and uncertainty regarding future climate provide new challenges for the conservation of endangered tree species. For example, threat status can be impacted by genetic diversity, where forest trees show reduced geographic range size, isolated populations and fragmented distribution. We place the conservation insights of population genetic structure in a climate change context, using as experimental system a relict drought-sensitive fir (Abies pinsapo Boiss.). Nuclear (nSSR, ISSR) and chloroplast (cpSSR) markers were analysed to investigate the extent to that A. pinsapo evidences ongoing genetic erosion, isolation and divergent genetic diversity, among populations, elevations and cohorts (young, adult and old trees). We obtained contrasting patterns among chloroplast and nuclear markers. Based on cpSSRs, the highest genetic distances were found in the western portion of the distribution, while based on both nSSRs and ISSRs, differentiation appeared in the eastern portion of the distribution. Evidence for bottlenecks and genetic drift were found in all the studied populations, as well as low among-population genetic differentiation. Land use legacies e.g. impacting current forest structural diversity might be related to observed genetic diversity. No evidence of demographic genetic erosion among cohorts were found. Conservation efforts should focus on reducing the probability of occurrence of stochastic events such as fires and habitat loss due to human impacts or climate change to maximise A. pinsapo population sizes. Further research on adaptive potential should focus on identifying active genetic management strategies that might improve adaptation to future climates in such endangered relict species.