REFOREST · The Role of extreme drought and legacy EFfects of long-term manipulatiOn of water availability on growth and REproduction of ScoTs pine REFOREST

The Role of extreme drought and legacy EFfects of long-term manipulatiOn of water availability on growth and REproduction of ScoTs pine REFOREST

Scots pine (Pinus sylvestris) and deciduous oak (e.g. Quercus petrea, Q. robur and Q. pubescens) are widely distributed tree species in Europe. Several recent studies conducted in southern Europe have reported drought-induced dieback of Scots pine. Many of those forests once dominated by Scots pine are now shifting towards the dominance of oak. Drought stress has been identified as an important driving factor for this transition of forest composition from Scots pine to oak. The future climate is expected to be associated with more frequent and longer drought events, which will challenge the acclimation potential (i.e., ability to grow and survive with environmental changes) of forest tree species. An important question in the debate on drought and acclimation is whether trees will be able to acclimate fast enough to cope with increased frequency and severity of droughts. It is therefore important to understand how tree growth responses to extreme droughts vary across sites with different productivity, since site productivity can modify trees growth and survival. In addition to adult tree responses to drought, the seedling growth and survival performances are key to forecast the future forest composition. Current global warming is happening too quickly for long-lived organisms such as trees to be able to adapt genetically to new living conditions through the process of evolution, which takes many generations. Fortunately, trees – like all plants – can respond very flexibly to their environment, for example by forming more roots in times of drought and more leaves (promoting strong growth) when conditions are good. However, these specific environmental adaptations are not handed down genetically to their offspring; the inherited genome only includes the ability for a tree to adapt itself. Consequently, it was long believed that the abilities acquired by an individual tree were lost from one generation to the next. It is only in recent years that scientists have discovered mechanisms in animals and humans that allow them to pass on responses to environmental influences to their offspring. These mechanisms take the form of small molecules, known as methyl groups, which are attached to DNA building blocks and help determine the extent to which individual genes are deployed. This pattern of molecular groups is transmitted to offspring via egg cells, sperm or pollen. In this context, the overall objectives of this study were to (1) quantify tree-level growth of the two common European tree species, Scots pine and deciduous oak along a latitudinal gradient from southern Spain to northern Germany with particular focus on the effects of severe drought events, and (2) quantify the potential role of mother trees environmental experiences to offspring growth and survival in variable growing conditions (water, temperature and shading).

Data: CORDIS, © European Union