Evolutionary Aspects of the Annual Cycle

Abstract

The hypothetico-deductive modelling framework introduced in Chap. 2 is applied to examining the evolutionary aspects of the annual cycle in boreal and temperate trees. For use of growth resources and competition (capacity adaptation), early onset and late cessation of growth are selected for. However, due to the risk of spring and autumn frost damage (survival adaptation), they are simultaneously selected against. This trade-off is examined by means of computer simulations with models representing various regulation principles of the annual cycle. Considerable differences among the principles are reported. When the principles are equally constrained for avoidance of frost damage, some of them allow the trees to use the growing season more comprehensively than others. Next, differences among the provenances of the tree species are examined within the framework of the modelling approach. The annual cycle of each provenance is adapted to its native climate, and this adaptation is manifested in several traits associated with the environmental regulation of the annual cycle. In the models of the annual cycle, this genetic differentiation is readily addressed via the values of the model parameters, such as critical night length of growth cessation or the chilling requirement of rest break. The possibilities of addressing the effects of the maternal environment on the annual cycle traits of the offspring are also discussed, and so is the emerging approach of combining genetic and ecophysiological modelling of the annual cycle.