The Annual Cycle Under Changing Climatic Conditions

Abstract

The hypothetico-deductive modelling framework introduced in Chap. 2 is applied to examining the effects of climatic change on the annual cycle of boreal and temperate trees. Most emphasis is devoted to the paradoxical hypothesis that climatic warming will increase the incidence of frost damage in these trees. According to early computer simulations, trees in boreal conditions in particular would deharden and even start to grow during such mild spells in winter as are commonly projected to prevail in the future climate, so that serious damage would result during subsequent periods of frost. Empirical tests of the frost damage hypothesis suggest that the catastrophic frost damage projected in the early computer simulations will not be realised. Even so, the frost damage hypothesis cannot be ruled out. Available experimental evidence remains limited, and theoretical work with computer simulations has shown that relatively small changes in the ecophysiological traits of trees may cause premature dehardening and growth onset during mild spells in the scenario climate. There have also been several reports of considerable frost damage to boreal and temperate trees and other plants in natural conditions after unseasonally warm spells in winter even in the present climate. For these reasons, nothing conclusive can be said about the frost damage hypothesis. However, the research discussed in this and other chapters of the present volume has pointed out not only the ecophysiological traits of the trees that are critical for the frost damage hypothesis but also the experimental designs that facilitate the determining of those traits in any tree population. Overall, the importance of ecophysiological realism and continuous critical testing of the models are emphasised. Finally, the implications of the effects of climatic change on tree seasonality to the stand and ecosystem level are briefly discussed.