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The global vegetation cover underwent strong changes during the past glacial cycle. These have been driven by climatic fluctuations but also by spatiotemporal vegetation dynamics, including migration to new climatologically suitable areas and interactions with other species. However, how much migration lag contributed to the vegetation change after the Last Glacial Maximum (LGM) is often not clear. We used the newly-implemented model LPJ-GM 2.0 to simulate the vegetation change of southern and central Europe from the end of the LGM (18.5 ka) to the preindustrial era (1.5 ka). The model couples a migration module to the dynamic global vegetation model LPJ-GUESS, thus allowing species to migrate simultaneously while interacting with each other. We compared two dispersal settings (free dispersal and dispersal limitation) against pollen data to test the reliability of the migration module to provide realistic paleo-vegetation reconstructions for biome and species distributions. Furthermore, we calculated range shifts of the leading edges and centroids to detect potential species-specific migration lags and range filling delays across simulation time. Our results show that the setting with dispersal limitation is better at capturing the initial post-glacial expansion of non-boreal forests in southern and central Europe than the scenario assuming free dispersal. Range shift analysis shows significant migration lags for most tree species at times of sudden temperature rise (start of the Bølling–Allerød warming event and following the Younger Dryas). Overall, our study suggests that it is necessary to include migration processes when simulating vegetation range expansion under rapid climate change, with implications for future vegetation projections.

The prediction of species geographic redistribution under climate change (i.e. range shifts) has been addressed by both experimental and modelling approaches and can be used to inform efficient policy measures on the functioning and services of future ecosystems. Dynamic Global Vegetation Models (DGVMs) are considered state-of-the art tools to understand and quantify the spatio-temporal dynamics of ecosystems at large scales and their response to changing environments. They can explicitly include local vegetation dynamics relevant to migration (establishment, growth, seed production), species-specific dispersal abilities and the competitive interactions with other species in the new environment. However, the inclusion of more detailed mechanistic formulations of range shift processes may also widen the overall uncertainty of the model. Thus, a quantification of these uncertainties is needed to evaluate and improve our confidence in the model predictions. In this study, we present an efficient assessment of parameter and model uncertainties combining low-cost analyses in successive steps: local sensitivity analysis, exploration of the performance landscape at extreme parameter values, and inclusion of relevant ecological processes in the model structure. This approach was tested on the newly-implemented migration module of the state-of-the-art DGVM, LPJ-GM 1.0. Estimates of post-glacial migration rates obtained from pollen and macrofossil records of dominant European tree taxa were used to test the model performance. The results indicate higher sensitivity of migration rates to parameters associated with the dispersal kernel (dispersal distances and kernel shape) compared to plant traits (germination rate and maximum fecundity) and highlight the importance of representing rare long-distance dispersal events via fat-tailed kernels. Overall, the successful parametrization and model selection of LPJ-GM will allow simulating plant migration with a more mechanistic approach at larger spatial and temporal scales, thus improving our efforts to understand past vegetation dynamics and predict future range shifts in a context of global change.

To what extent Pleistocene sea-level fluctuations have affected the genetic diversity of species is one of the current topics in biogeographical research. Carduncellus dianius is a Mediterranean narrow endemic species, restricted to < 20 populations distributed along coastal areas in Alicante (mainland eastern Iberian Peninsula) and on the island of Ibiza (Balearic Islands). To get insights into its evolutionary history and its genetic diversity and structure, we combined the analysis of molecular markers (three plastid DNA regions and AFLP) with ecological niche modelling. Results from dated phylogeographical analyses revealed that this species might have originated in the continental region during the early Pleistocene. The colonization of Ibiza could have occurred by a single long-distance dispersal event, with a subsequent back-colonization from the island to the same continental area of origin. These results corroborate the role of islands as sources for mainland colonization (biodiversity reservoirs) and as refugia during glacial periods. Notably, we detected that populations located on stable landmasses (i.e. not affected by sea rising during interglacial cycles) harboured significantly higher genetic diversity than those that were periodically submerged during the periods of marine transgressions. Our results point out sea-level fluctuations as a factor to be considered in phylogeographical studies focused on species distributed along coastlines., Financial support from the Spanish Ministerio de Ciencia e Innovación (Projects CGL2007-60781 and CGL2010/18631) and the Catalan government (‘Ajuts a grups consolidats’ 2009/SGR/439 and 2014/SGR/514 and 2017-SGR1116) is also acknowledged.

Our study showed that increases in seasonal productivity drive earlier autumn senescence of temperate trees. Norby argues that this finding is contradicted by observations from free-air CO 2 enrichment (FACE) experiments, where elevated CO 2 has been found to delay senescence in some cases. We provide a detailed answer showing that the results from FACE studies are in agreement with our conclusions.

Limits to the growing season The length of the growing season in temperate forests has been increasing under recent climate change because of earlier leaf emergence and later leaf senescence. However, Zani et al. show that this trend might be reversed as increasing photosynthetic productivity begins to drive earlier autumn leaf senescence (see the Perspective by Rollinson). Using a combination of experimental, observational, and modeling studies based on European forest trees, the researchers conclude that leaf senescence will advance by 3 to 6 days by the end of the 21st century rather than lengthening by 1 to 3 weeks as current phenological models have predicted. In turn, this predicted phenological pattern will limit the capacity of temperate forests to mitigate climate change through carbon uptake. Science , this issue p. 1066 ; see also p. 1030

Ecological Research, 32 (6), ISSN:0912-3814