The long-term survival of populations depends on genetic variation in traits related to survival and reproductive fitness. The polygenic architecture of traits is thought to facilitate adaptive shifts, but whether tree species will be able to adapt to the currently rapidly changing climatic conditions remains a subject of debate. On the other hand, trees are characterized by considerable phenotypic plasticity that allows them to grow under different or variable environmental conditions caused by global climate change. Phenotypic plasticity may thus help populations survive by “buying time” until genetic adaptation to the new environmental conditions occurs. One of the most important mechanisms underlying phenotypic plasticity is epigenetic regulation—stable altered gene expression without changes to the DNA sequence. Efficient dispersal mechanisms and the high fecundity of forest trees can promote genetic connectivity and facilitate the spread of adaptive genes and the colonization of new habitats. However, the colonization of new areas in response to a shift in suitable habitats, for example by northward migration, requires the dispersal of diploid sporophytes by seeds or fruits. Natural dispersion of tree species is therefore likely largely lagging behind the expansion of potentially suitable habitats dependent on the genetic system of species.