Climate change poses major challenges for forest tree species across the European continent. The ongoing climate warming will result in fundamental ecological changes of species habitats and will confront European tree species with increasing drought events.
However, tree species are not uniform biological units, but evolved through natural selection to distinct intraspecific genetic ecotypes adapted to local environments. Progenies originating from different ecological conditions may differ in morphological or phenological traits, varying in their ability to react to environmental changes. Consequently, the origin of seed sources exhibit levels of adaptation within the species ecological amplitude (i.e. the range of environmental conditions an organism can survive and function) and the site-specific choice of seed sources used in reforestations is an essential part of sustainable forest management and a key function in mitigating climate-induced maladaptation.
Sustainable reforestation strategies must therefore consider the adequate choice of seed sources, which have to match the planting side conditions and contain proper genetic information to adapt to future climate. As climate change is supposed to result in major environmental changes on a short timescale compared to the generation time of tree species, natural adaptation processes of tree populations might not be fast enough to compensate negative consequences on forest functions.
Afforestation decision circle
Sustainable forest management should include the adequate choice of seed sources for reforestations, which meet the future site conditions. The figure below illustrates a simplified decision pathway for a reforestation plot.
Despite the necessity for forest managers to react to climate change, local guidelines for transfer of forest reproductive material (FRM) are still mainly focused on regional and static seed sources. They mostly recommend autochthonous and geographically proximal populations, because these are supposed to be adapted to the current local climate. However, such populations are phenotypically selected and thus often grow on the most productive soils. But, how meaningful is it to use FRM from such populations, adapted to favourable and present-day environmental conditions, in order to establish forests capable of coping with the anticipated climate change?
What are the alternatives?
Forest reproductive material (FRM)
Any part of a tree that can be used for artificial regeneration such as sowing and planting. In most cases, the term refers to seed and seedlings. The marketing and use of FRM is regulated by European and international legislation including quality criteria and trackable data-collection.
For further information check the EUFORGEN FRM information booklet.
To mitigate climate-induced genetic maladaptation, enhancing the frequency of pre-adapted genes (i.e. implemented as transfer of pre-adapted FRM) is discussed as a promising tool to increase forest stability. These concepts are mostly based on bioclimatic models to indicate source populations associated with a warmer and more arid climate. These source populations can then serve for afforestation on sites within the species’ range, which will feature similar climatic characteristics in the future.
Several FRM transfer strategies have been developed, including (i) the translocation of FRM at a limited regional scale, (ii) a combined approach ("mix and match"), where suitable seeds from several populations are mixed and translocated, or (iii) the use of FRM with a very high genetic diversity, assuming that it represents populations with a very high adaptive potential. All of these approaches have one thing in common: They require detailed knowledge of genetic diversity, adaptive mechanisms, fitness-relevant traits, and habitat characteristics.
In ACORN, we propose the use of genetic and genomic tools in combination with common garden experiments in order to identify drought-adapted populations both at regional and interregional (continental) scales. This knowledge will serve as a basis for selecting such populations as future seed sources with the intention of mitigating the effects of climate change.
In particular, ACORN raises the following research questions:
Are there genes and genomic regions undergoing natural selection for drought tolerance at the regional and the interregional scale?
Are there common genomic signatures of adaptation to drought within and between climatically different regions?
Can we find genomic mechanisms behind traits involved in drought responses at the regional and interregional scale?
Will FRM transfer at the regional and/or interregional scale significantly increase the adaptive capacity of future forests?
Which strategy of FRM transfer is optimal in order to increase benefits in terms of adaptive capacity and minimize the risk of maladaptation?