Towards an understanding of the response of southern European vegetation to orbital and suborbital climate variability

Abstract

In recent years, the generation of high-resolution terrestrial and marine long pollen sequences with improved chronological control has provided new insights into the vegetation response in southern Europe to orbital and suborbital climate variability. Here a synthesis of our current understanding of the phase and amplitude relationships between climate forcing and vegetation changes is presented. What emerges is that on orbital frequencies the timing of interglacial forest expansion is closely linked to the summer insolation maximum, but does not have a fixed lag relative to the mid-point of the deglaciation, which may vary from one Termination to another. For the closing phases of interglacials, the available evidence suggests that forest in southern Europe usually extends into the interval of ice growth. However, suborbital variability may override the diachronous relationship between glacial inception and forest decline, leading to a premature ending of forest periods. During glacial intervals, there is a close correspondence between tree-population size and ice volume extent, while during temperate intervals, the extent of forest development is closely related to the amplitude of insolation and associated climate regimes, but may diverge from the extent of residual ice volume. On suborbital frequencies, changes in tree-population size are in phase with climate forcing, while the amplitude of these changes is modulated by geographical position and local factors. Finally, orbital mean state can lead to the modulation of the amplitude of suborbital-scale variability. Examination of additional climatic cycles and increased resolution (better than 200 years) are needed to test further these preliminary conclusions.