Changes in the growing-season lengths of temperate trees greatly affect biotic interactions and global carbon balance. Yet future growing-season trajectories remain highly uncertain because the environmental drivers of autumn leaf senescence are poorly understood. Using experiments and long-term observations, we show that increases in spring and summer productivity due to elevated carbon dioxide, temperature, or light levels drive earlier senescence. Accounting for this effect improved the accuracy of senescence predictions by 27 to 42% and reversed future predictions from a previously expected 2- to 3-week delay over the rest of the century to an advance of 3 to 6 days. These findings demonstrate the critical role of sink limitation in governing the end of seasonal activity and reveal important constraints on future growing-season lengths and carbon uptake of trees.

Seed longevity derived from artificial ageing experiments has been shown to be related to the macroclimate at the sampling site and with individual seed traits. Nevertheless, the ecological interpretation of artificial seed longevity remains to be clarified. In this article, the ecological significance of seed longevity expressed by the p50 index was explored using 16 closely related populations of the genus Silene L. Seeds were subjected to an artificial ageing treatment at 45 °C, 60% relative humidity and regularly tested for germination. The decline of viability to 50% (p50 index) was calculated using probit analysis. Its relationship with known ecological predictors of seed longevity was assessed by multiple regression analysis. Values of p50 ranged from 3.7 to 68.3 days. Seed lots which normally experience drought during the post‐zygotic phase in a dry, warm environment, were long‐lived. Consistently, precipitation during the driest months of the reproductive period was the strongest predictor of p50 variability (partial regression, R2 = 0.424). We could not find any relationship between ex situ seed longevity and soil seed bank formation or seed size. Our results indicate that ex situ seed longevity has an ecological significance related to long‐term climatic differences at population site. Increased longevity presumably reflects resistance to desiccation stress attained by seeds through local adaptation to warm, dry climates. We cannot exclude that seed tolerance to ageing could also represent phenotypic plasticity mediated by a drier maturation environment. The vulnerability of seeds from wet, cool climates and the adaptive response of seed longevity to different environments may have implications for ex situ conservation in the face of climate warming.

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 CO2 enrichment (FACE) experiments, where elevated CO2 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.

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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.

Abstract. 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 (propagule) 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, focusing on European forests. 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 plant migration to be simulated 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.

No abstract

Abstract. 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.