Climate and abrupt vegetation change in Northern Europe since the last deglaciation

A long-standing question in palaeoecology has been to determine the importance of climate 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 generalized additive mixed models were applied to investigate the underlying dynamics of two periods of higher rates of turnover: the Younger Dryas-early Holocene transition (YD-EH; 11.6-9.0kyr) and early-middle Holocene (EMH; 9.0-6.0kyr). Results revealed a high frequency of turnover events between 12.75-11.5, 10.75-11, 10.25-10, 7.75-7.25, 3.25-3.0 and 1.75-.25kyr. Furthermore, there was a strong linear relationship between pollen assemblage turnover and large directional temperature changes during the abrupt climate changes of the Lateglacial-early Holocene transition. In contrast, patterns of turnover during the Holocene were generally site-specific and 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 were 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 result in these different responses and whether this rate is the same across biomes.