Patterns of adaptive genetic variation in forest tree species; the reproductive enviroment as an evolutionary force in Picea abies

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Common garden plantations have provided data for studies of the variability in quantitative adaptive traits among and within wild populations of forest tree species. The distribution of variability among and within populations, its patterns across the landscape and relationships to environmental variables have been used to interpret the ecological basis for genetic differentiation and evolution of the species (Rehfeldt 1988, 1989,1995; Campbell et al. 1989). The studies have shown that climatic adaptation seems to be the most important component in the evolutionary process of temperate and boreal conifers. Most species show substantial variability in adaptive traits both within and among populations, even at the climatic margin of their range (Savolainen 1997). The main evolutionary forces influencing the variability patterns are natural selection, genetic drill, gene flow, mutations and phenotypic plasticity (Eriksson 1998a). The marry types of variability patterns shown by different species and their degree of adaptedness to the sites suggest that species occupying the same environment may be influenced by different evolutionary forces, see examples discussed by Eriksson (1998b). Several selective forces may even operate on the same population, some simultaneously and some at different life stages or during different seasons of the year (Eriksson 1998a). The variability patterns are therefore most likely under the influence of several evolutionary forces interacting in rather complex ways. This conclusion is supported by the rather high levels of genetic variation in survival and annual growth rhythm traits maintained in the boreal forest (Savolainen 1997), in spite of a strong directional selection against the traits.