Climate and abrupt vegetation change in Northern Europe during the Lateglacial and Holocene.

Abstract:

A long-standing question in palaeoecology has been to determine the importance of climate in driving vegetation change since the last deglaciation. Here, we investigate the local-to-regional dynamics of vegetation change during the Lateglacial and the Holocene in Northern Europe. We extracted sites from the European Pollen Database and used the squared-chord distance (SCD) dissimilarity metric to identify time periods of high pollen assemblage turnover representing periods of abrupt vegetation change. In addition, a set of generalised additive mixed models were applied to investigate the underlying dynamics of two periods of higher rates of turnover: the Younger Dryas–Early Holocene transition (11.6-9.0 ka) and Early–Middle Holocene (9.0-6.0 ka). Results indicated that consistently high SCDs were found during the abrupt climate changes of the Lateglacial–Early Holocene transition, and there was a strong linear relationship between pollen assemblage turnover and large directional temperature changes at this time. In contrast, patterns of turnover during the climatic events during the Holocene were site specific. During the EMH we found evidence that the vegetation response was non-linear and highly variable across and between regions. Our results have implications for understanding the relationship between threshold dynamics and the amplitude of an extrinsic forcing. Across the Lateglacial–Early Holocene boundary the rate and magnitude of temperature change was large enough to override any site-specific thresholds, resulting in large assemblage turnovers. In contrast, during the Holocene the vegetation response was mediated by intrinsic factors, which resulted in varying turnover rates between regions. The next research challenge is to attempt to determine whether it is possible to appreciate the velocity and rate of change that is necessary to illicit these different responses– and whether this rate is the same across biomes.