目次

International audienceRecent climate change will presumably allow many plant species to expand their geographical range up to several hundred kilometres towards the poles within a few decades. Much uncertainty exists however to which extent species will actually be able to keep pace with a rapidly changing climate. A suite of direct and indirect research approaches have explored the phenomenon of range expansions, and the existing evidence is scattered across the literature of diverse research subdisciplines. Here I attempt to synthesise the available information within a population ecological framework in order to evaluate implications of patterns of seed dispersal and initial population establishment for range expansions. After introducing different study approaches and their respective contributions. I review the empirical evidence for the role of long-distance seed dispersal in past and ongoing expansions. Then I examine how some major ecological determinants of seed dispersal and colonisation processes - population fecundity, dispersal pathways, arrival site conditions, and biotic interactions during recruitment - could be altered by a rapidly changing climate. While there is broad consensus that long-distance dispersal is likely to be critical for rapid range expansions, it remains challenging to relate dispersal processes and pathways with the establishment of pioneer populations ahead of the continuous species range. Further transdisciplinary efforts are clearly needed to address this link, key for understanding how plant populations 'move' across changing landscapes

Greater capacity to exploit warming temperatures in northern populations of European beech is partly driven by delayed leaf senescence

One of the most widespread consequences of climate change is the disruption of trees’ phenological cycles. The extent to which tree phenology varies with local climate is largely genetically determined, and while a combination of temperature and photoperiodic cues are typically found to trigger bud burst (BB) in spring, it has proven harder to identify the main cues driving leaf senescence (LS) in autumn. We used 905 individual field observations of BB and LS from six Fagus sylvatica populations, covering the range of environmental conditions found across the species distribution, to: (i) estimate the dates of BB and LS of these populations; (ii) assess the main drivers of LS; and (iii) predict the likely variation in growing season length (GSL; defined as the period from BB to LS timing) across populations under current and future climate scenarios. To this end, we first calibrated linear mixed-effects models for LS as a function of temperature, insolation and BB date. Secondly, we calculated GSL for each population as the number of days between BB and LS. We found that: i) there were larger differences among populations in the date of BB than in the date of LS; ii) the temperature through September, October and November was the main determinant of LS, although covariation of temperature with daily insolation and precipitation-related variables suggests that all three variables may affect LS timing; and iii) GSL was predicted to increase in northern populations and to shrink in central and southern populations under climate change. Consequently, the large present-day differences in GSL across the range of beech are likely to decrease under future climates where rising temperatures will alter the relationship between BB and LS. Northern populations are likely to increase their productivity as warmer conditions will enable them to extend their growing season.Peer reviewe

Revegetation through seeding or planting: A worldwide systematic map

Roughly 2 billion ha of land are degraded and in need of ecological restoration worldwide. Active restoration frequently involves revegetation, which leads to the dilemma of whether to conduct direct seeding or to plant nursery-grown seedlings. The choice of revegetation method can regulate plant survival and performance, with economic implications that ultimately feed back to our capacity to conduct restoration. We followed a peer -reviewed protocol to develop a systematic map that collates, describes and catalogues the available studies on how seeding compares to planting in achieving restoration targets. We compiled a database with the charac-teristics of all retrieved studies, which can be searched to identify studies of particular locations and habitats, objectives of restoration, plant material, technical aspects, and outcomes measured. The search was made in eight languages and retrieved 3355 publications, of which 178 were retained. The systematic map identifies research gaps, such as a lack of studies in the global South, in tropical rainforests, and covering a long time period, which represent opportunities to expand field-based research. Additionally, many studies overlooked reporting on important technical aspects such as seed provenance and nursery cultivation methods, and others such as watering or seedling protection were more frequently applied for planting than for seeding, which limits our capacity to learn from past research. Most studies measured outcomes related to the target plants but avoided measuring general restoration outcomes or economic aspects. This represents a relevant gap in research, as the choice of revegetation method is greatly based on economic aspects and the achievement of restoration goals goes beyond the establishment of plants. Finally, we identified a substantial volume of studies conducted in temperate regions and over short periods (0-5 y). This research cluster calls for a future in-depth synthesis, potentially through meta-analysis, to reveal the overall balance between seeding and planting and assess whether the response to this question is mediated by species traits, environmental characteristics, or technical aspects. Besides identifying research clusters and gaps, the systematic map database allows managers to find the most relevant scientific literature on the appropriateness of seeding vs. planting for particular conditions, such as certain species or habitats

Maternal effects shape the seed mycobiome in Quercus petraea

The tree seed mycobiome has received little attention despite its potential role in forest regeneration and health. The aim of the present study was to analyze the processes shaping the composition of seed fungal communities in natural forests as seeds transition from the mother plant to the ground for establishment. We used metabarcoding approaches and confocal microscopy to analyze the fungal communities of seeds collected in the canopy and on the ground in four natural populations of sessile oak (Quercus petraea). Ecological processes shaping the seed mycobiome were inferred using joint species distribution models. Fungi were present in seed internal tissues, including the embryo. The seed mycobiome differed among oak populations and trees within the same population. Its composition was largely influenced by the mother, with weak significant environmental influences. The models also revealed several probable interactions among fungal pathogens and mycoparasites. Our results demonstrate that maternal effects, environmental filtering and biotic interactions all shape the seed mycobiome of sessile oak. They provide a starting point for future research aimed at understanding how maternal genes and environments interact to control the vertical transmission of fungal species that could then influence seed dispersal and germination, and seedling recruitment.Peer reviewe

Spatial patterns of genus-level phylogenetic endemism in the tree flora of Mediterranean Europe

Aim: The Mediterranean Basin is a major hotspot of plant biodiversity, including forest trees. Over the past centuries, Mediterranean forests have been fragmented and over-exploited, to which the threats of climate change are now added. Our aim is to better understand patterns and processes of tree biodiversity in the Mediterranean and to provide indicators complementing the traditional approaches to biodiversity conservation based on species counts and occurrences, using georeferenced phylogenetic diversity and endemism analyses in a spatial ecological context. Location: Mediterranean Europe. Methods: Using a dated phylogeny of the 64 Euro-Mediterranean tree genera, we calculated phylogenetic diversity for all 50 × 50 km2 grid cells spanning Mediterranean Europe (n = 643) and compared values with those obtained for genus-level taxonomic diversity. Then, we tested the relative influence of geography, past and present climate, and soil on tree diversity (phylogenetic or taxonomic) and its geographical turnover. Geographical patterns of phylogenetic endemism were inferred using the Categorical Analyses of Neo- and Paleo-Endemism (CANAPE) methodology. Results: We showed that phylogenetic and taxonomic diversity within and among cells are correlated and influenced by soil parameters as well as current, Holocene and Late Glacial Maximum climate. Southern Spain, Cyprus and some Aegean islands contained areas of disproportionately high phylogenetic diversity and a concentration of phylogenetic paleo-endemics, while phylogenetic neo-endemism was high in eastern Sicily. Mixed phylogenetic endemism regions were detected in southern Spain and Portugal, in the Balkans and in Crete. Main conclusions: Our phylogenetic approach provides relevant indicators for better protecting forests of the Mediterranean, encompassing past and present evolutionary processes and factors. We consider areas that show a concentration of evolutionary history manifested by high phylogenetic endemism as high priority targets for the conservation of the European tree flora.Aix-Marseille University ANR-11-LABX-006

Widespread latitudinal asymmetry in the performance of marginal populations: A meta-analysis

Aim Range shifts are expected to occur when populations at one range margin perform better than those at the other margin, yet no global trend in population performances at range margins has been demonstrated empirically across a wide range of taxa and biomes. Here we test the prediction that, if impacts of ongoing climate change on performance in marginal populations are widespread, then populations from the high-latitude margin (HLM) should perform as well as or better than central populations, whereas low-latitude margin (LLM) populations should perform worse. Location Global. Time period 1995–2019. Major taxa studied Plants and animals. Methods To test our prediction, we used a meta-analysis to quantify empirical support for asymmetry in the performance of high- and low-latitude margin populations compared to central populations. Performance estimates (survival, reproduction, or lifetime fitness) for populations occurring in their natural environment were derived from 51 papers involving 113 margin-centre comparisons from 54 species and 705 populations from the Americas, Europe, Africa and Australia. We then related these performance differences to climatic differences among populations. We also tested whether patterns are consistent across taxonomic kingdoms (plants vs animals) and across realms (marine vs terrestrial). Results Populations at margins performed significantly worse than central populations, and this trend was primarily driven by the low-latitude margin. Although the difference was of small magnitude, it was largely consistent across biological kingdoms and realms. Differences in performance were weakly (p = .08) related to the difference in average temperatures between central and marginal populations. Main conclusions The observed asymmetry in performance in marginal populations is consistent with predictions about the effects of global climate change, though further research is needed to confirm the effect of climate. It indicates that changes in demographic rates in marginal populations can serve as early-warning signals of impending range shifts

Forest microclimates and climate change: importance, drivers and future research agenda

Forest microclimates contrast strongly with the climate outside forests. To fully understand and better predict how forests' biodiversity and functions relate to climate and climate change, microclimates need to be integrated into ecological research. Despite the potentially broad impact of microclimates on the response of forest ecosystems to global change, our understanding of how microclimates within and below tree canopies modulate biotic responses to global change at the species, community and ecosystem level is still limited. Here, we review how spatial and temporal variation in forest microclimates result from an interplay of forest features, local water balance, topography and landscape composition. We first stress and exemplify the importance of considering forest microclimates to understand variation in biodiversity and ecosystem functions across forest landscapes. Next, we explain how macroclimate warming (of the free atmosphere) can affect microclimates, and vice versa, via interactions with land-use changes across different biomes. Finally, we perform a priority ranking of future research avenues at the interface of microclimate ecology and global change biology, with a specific focus on three key themes: (1) disentangling the abiotic and biotic drivers and feedbacks of forest microclimates; (2) global and regional mapping and predictions of forest microclimates; and (3) the impacts of microclimate on forest biodiversity and ecosystem functioning in the face of climate change. The availability of microclimatic data will significantly increase in the coming decades, characterizing climate variability at unprecedented spatial and temporal scales relevant to biological processes in forests. This will revolutionize our understanding of the dynamics, drivers and implications of forest microclimates on biodiversity and ecological functions, and the impacts of global changes. In order to support the sustainable use of forests and to secure their biodiversity and ecosystem services for future generations, microclimates cannot be ignored.Peer reviewe

Herbivory on the pedunculate oak along an urbanization gradient in Europe : Effects of impervious surface, local tree cover, and insect feeding guild

Urbanization is an important driver of the diversity and abundance of tree-associated insect herbivores, but its consequences for insect herbivory are poorly understood. A likely source of variability among studies is the insufficient consideration of intra-urban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effects of local canopy cover and percentage of impervious surface on insect herbivory in the pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe. We found that the damage caused by chewing insect herbivores as well as the incidence of leaf-mining and gall-inducing herbivores consistently decreased with increasing impervious surface around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of impervious surface. In contrast, an increase in local canopy cover buffered the negative effect of impervious surface on leaf miners and strengthened its effect on gall inducers. These results show that-just like in non-urban areas-plant-herbivore interactions in cities are structured by a complex set of interacting factors. This highlights that local habitat characteristics within cities have the potential to attenuate or modify the effect of impervious surfaces on biotic interactions.Peer reviewe

Search for top-down and bottom-up drivers of latitudinal trends in insect herbivory in oak trees in Europe

International audienceAim: The strength of species interactions is traditionally expected to increase toward the Equator. However, recent studies have reported opposite or inconsistent latitudinal trends in the bottom-up (plant quality) and top-down (natural enemies) forces driving herbivory. In addition, these forces have rarely been studied together thus limiting previous attempts to understand the effect of large-scale climatic gradients on herbivory. Location: Europe. Time period: 2018–2019. Major taxa studied: Quercus robur. Methods: We simultaneously tested for latitudinal variation in plant–herbivore–natural enemy interactions. We further investigated the underlying climatic factors associated with variation in herbivory, leaf chemistry and attack rates in Quercus robur across its complete latitudinal range in Europe. We quantified insect leaf damage and the incidence of specialist herbivores as well as leaf chemistry and bird attack rates on dummy caterpillars on 261 oak trees. Results: Climatic factors rather than latitude per se were the best predictors of the large-scale (geographical) variation in the incidence of gall-inducers and leaf-miners as well as in leaf nutritional content. However, leaf damage, plant chemical defences (leaf phenolics) and bird attack rates were not influenced by climatic factors or latitude. The incidence of leaf-miners increased with increasing concentrations of hydrolysable tannins, whereas the incidence of gall-inducers increased with increasing leaf soluble sugar concentration and decreased with increasing leaf C : N ratios and lignins. However, leaf traits and bird attack rates did not vary with leaf damage. Main conclusions: These findings help to refine our understanding of the bottom-up and top-down mechanisms driving geographical variation in plant–herbivore interactions, and indicate the need for further examination of the drivers of herbivory on trees