What does climate change mean for the sessile oak?

A team of Hungarian scientists who are partners in FORGER  have studied for the first time the potential impact of climate change on intra-specific diversity of sessile oak (Quercus petraea), focusing on marginal tree populations. The geographical distribution of sessile oak, similarly to other dominant tree species, finds its limits in the low altitude, low elevation and dry conditions of South-Eastern Europe.

Future scenarios derived from models show that climatic factors, such as early summer precipitation and late summer temperature, are going to determine where sessile oak will be able to grow. Furthermore, extreme events, such as repeated droughts, can have major effect on sessile oak close to the margins of its distribution range.Photo: Quercus petraea. Credit: Bioversity International/B.Vinceti

It is predicted that the South-Eastern European region will be subject to declining precipitation, warming, and increasing frequency of droughts. However, very few analyses of climate-driven selection pressures have so far concentrated on forests found at low-elevation forests at xeric limit (with moisture as limiting factor) of the distribution of sessile oak, in areas where the species is retracting.

The investigation concentrated on portions of the DNA sequence in chromosomes (loci) that contains genes controlling important physiological functions, likely affected by influence of climatic factors. The study suggests that climatic stress may lead to significant directional selection which is a mode of natural selection through which individuals with particular characteristics are favored over others. It causes the advantageous variants of a particular gene (alleles) to increase as a consequence of differences in survival and reproduction. This information helps interpret the patterns of genetic diversity in marginal tree populations, exposed to environmental pressure.

Results suggest that temperature and precipitation do exert their effects on specific regions of a chromosome where genes are located. The study also indicates that at warmer and drier sites, robust climatic selection might cause the decline of diversity and the higher level of fixation observed, meaning that in a certain tree population all individuals have the same single gene variant (allele) at a particular locus.

If these results are supported by additional studies, they may provide guidelines on how to conserve and use forest reproductive material originating from locations exposed to severe selection.

Text based on 'Decline of genetic diversity of sessile oak at the retracting (xeric) limits.' by Attila Borovics & Csaba Mátyás on Annals of Forest Science.

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