Evolutionary consequences of historic anthropogenic impacts on forest trees in Europe

Throughout history, man has strongly utilized and affected forest genetic resources in Europe. From an evolutionary perspective deforestation/fragmentation (→genetic drift), transfer of seeds and plants to new environments (→mainly gene flow) and selective logging (→selection) are most relevant and have been particularly addressed in this review. In contrast to most conifers, broadleaved tree populations have been especially reduced by historic fragmentation, and consequently, the related genetic effects have been possibly more pronounced. Widespread wind-pollinated species with wind/animal dispersed seeds appear to be more resilient to fragmentation than species with e.g. small geographic ranges and gravity dispersed seeds. In addition, naturally fragmented populations in the range margins may be more vulnerable than central populations as conditions for gene flow are generally impaired in peripheral areas. Traits important for adaptation (e.g. bud burst, bud set) are controlled by many genes, and as a corollary of fragmentation such genes are lost at a low rate. Large scale commercial translocation of seeds and plants for forestry purposes applies mostly to conifers and dates back about two centuries. Although many translocations have been successful in a forestry perspective, exposure to new selective regimes has sometimes challenged the adaptive limits of populations and caused setbacks or even diebacks of populations, as well as influencing neighbouring populations with maladapted genes (e.g. Scots pine, maritime pine, larch). Many tree species have substantial plasticity in fitness-related traits, which is vital for survival and viability following translocations. Selective logging has been practiced in Europe over the last two centuries and implies removal of superior trees with respect to growth and quality. Such traits are partly under genetic control. Consequent removal of superior trees may therefore have negative effects on the remaining gene pool, but this effect will also be counteracted by extensive gene flow. Although humans have strongly affected European forest trees over the last millennia, we argue that they are still resilient from an evolutionary perspective.