ACORN - Identifying seed sources for highly adaptable oak forests in a changing climate

Abstract

In the face of climate change, drought-adapted forest stands may serve as seed sources to increase the resilience of future forests. Assisted gene flow (AGF) describes the transfer of reproductive material from source populations currently featuring the anticipated environmental conditions and genetic composition of the planting site, within a species range. AGF aims to facilitate adaptation in a changing climate, as natural migration and adaptation may lag behind the pace of environmental change. Genetic studies are crucial in order to identify populations suitable for AGF. The ACORN-project applied molecular and quantitative genetic and genomic tools, in order to investigate drought adaptation and inform AGF strategies in European white oaks. It focused on three widely distributed species (Quercus petraea, Q. pubescens and Q. robur) with an important role in a climate-smart forestry. The species’ large distribution areas and wide ecological amplitude enable addressing the issue of drought adaptation at different geographic scales. By studying more than 120 populations, it was shown that past migration and landscape barriers like mountain changes resulted in a significant spatial genetic structure among, but not within regions. Association between environmental parameters, like precipitation seasonality and soil water storage capacity, and genomic variation suggests that natural selection at certain genes led to adaptation to harsh environmental conditions. The results show signatures of such an adaptation at a large scale, along environmental gradients, but also locally. At the local scale, this was demonstrated by comparing closely situated population pairs, each one growing on an arid site vs. a site with good water availability. A further approach was to test physiological differences between progenies of selected study populations growing in three different common gardens established near Zurich, Vienna and Ankara and link them to genomic variation. This experiment indicated a high level of phenotypic plasticity and that water use efficiency might differ even between progenies of closely situated populations as a result of adaptation to different water supply regimes. Furthermore, at the continent-wide scale certain gene loci were found to be significantly associated to traits related to drought stress tolerance, thus suggesting adaptation via natural selection. In summary, small scale AGF may be a low-risk option to increase climate resilience. Exchange with stakeholders showed that AGF in practice is limited for practical reasons (legislation, regulations, seed availability). Finally, it showed that a better communication of research results to practitioners is paramount in order to implement climate-smart seed sourcing strategies.