Background/Question/Methods   The transition from the last glacial period to the present interglacial was marked by a well-known series of rapid climatic changes between the Bolling-Allerod and the Younger Dryas. Although these do not provide exact analogs for future climate change, the rapidity of these changes is of the same orde of magnitude as that expected under future global change scenarios. We have used paleoecological records at a variety of spatial scale to examine the extent and magnitude of the impacts of these climatic fluctuations on ecosystem composition and structure.

Results/Conclusions   While both periods have global impacts on ecosystem change, the Bolling-Allerod appears to be more homogenous, with a general increase in functional and ecosystem diversity across the globe. This is due in part to the nature of the main external driver. The cold Younger Dryas has a marked effect in the circum-Atlantic region, causing fragmentation of the temperate vegetation developed during the Bolling-Allerod, but this attenuates with distance. In the southern hemisphere, the southward migration of the ITCZ and associated higher moisture results in increased forest cover. Taken together, the results show the ability of ecosystems to track these rapid changes, as well as the vulnerability of populations established under a new conditions to climatic reversals.