The pace of Holocene vegetation change: Although much is known about the rapid environmental changes that have occurred since the Industrial Revolution, the patterns of change over the preceding millennia have been only patchily understood. Using a global set of >1100 fossil pollen records, Mottlet al.explored the rates of vegetation change over the past 18,000 years (see the Perspective by Overpeck and Breshears). The authors show that the rates of change accelerated markedly during the Late Holocene (∼4.6 to 2.9 thousand years ago), even more rapidly than the climate-driven vegetation changes associated with the end of the last glacial period. In addition, the Late Holocene acceleration began for terrestrial communities as a whole, suggesting that the acceleration in turnover over the past two centuries is the tip of a deeper trend.Science, abg1685, this issue p.860; see also abi9902, p.786

Summary: Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science. They are an effective way to identify research foci that advance the field and that also have high policy and conservation relevance. To date, there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct past ecological and environmental systems on time‐scales from decades to millions of years. We adapted a well‐established methodology to identify 50 priority research questions in palaeoecology. Using a set of criteria designed to identify realistic and achievable research goals, we selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. The integration of online participation, both before and during the workshop, increased international engagement in question selection. The questions selected are structured around six themes: human–environment interactions in the Anthropocene; biodiversity, conservation and novel ecosystems; biodiversity over long time‐scales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesizing information from multiple records; and new developments in palaeoecology. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes and the continued application of long‐term data for better‐informed landscape management. Synthesis. Palaeoecology is a vibrant and thriving discipline, and these 50 priority questions highlight its potential for addressing both pure (e.g. ecological and evolutionary, methodological) and applied (e.g. environmental and conservation) issues related to ecological science and global change.

There is a rapidly emerging interest in detecting and understanding biodiversity trends during the ‘Anthropocene’ in response to human stressors and climate change. Surprisingly few studies have, however, considered trends in biodiversity during the preceding Holocene. Here, we present general trends in terrestrial alpha- and beta-diversity and biomass for the four main ecological phases (protocratic, mesocratic, Homo sapiens, oligocratic) of the Holocene in north-west Europe based on palynological data at the meta-community scale. Alpha- and beta-diversity decreased in the protocratic, showed little change in the mesocratic, decreased in the oligocratic, and increased markedly in the Homo sapiens phase. Biomass was maximal in the mesocratic. Biodiversity changes in the last 200 years (‘Anthropocene’), as detected from palynological data, are small compared with the changes over the Holocene. There are minor decreases in α-diversity, spatial β-diversity and biomass and a slight increase in temporal β-diversity at sites on fertile soils. This analysis is designed to encourage ecologists and biogeographers interested in the ‘Anthropocene’ to extend the time-scale of their analyses and to consider whether ‘Anthropocene’ biodiversity trends are a simple continuation of trends in the late Holocene or whether recent ‘Anthropocene’ trends deviate from the long-term Holocene trends. Hopefully, it will also stimulate palaeoecologists to consider Holocene biodiversity trends in different geographical areas and different organism groups and ecological systems.

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; 11.6–9.0 kyr) and early–middle Holocene (EMH; 9.0–6.0 kyr). 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–.25 kyr. 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.