Forest canopies buffer climate extremes in the understory. This buffering capacity is key to explain understory biodiversity and forest regeneration, and thus forest resilience to climate change. It is also important for recreational activities. Forest management practices impact these ecosystem services by modifying forest structure and composition, and thus understory microclimate. Today, however, forest managers have no tool to quantify the impact of their practices on understory microclimate, notably in terms of climate extremes or under future climate conditions. The objective of MaCCMic is to develop such tools that will help identify the main factors influencing forest understory microclimate and anticipate the impact of forest management (density, fragmentation, thinning, choice of species, understory removal, etc.) and climate change on forest microclimate and understory vegetation, notably in terms of climate extremes. Bringing together long-term datasets of understory microclimate, state-of-the-art LiDAR and Sentinel2 products and biophysical forest microclimate modelling, we will quantify how understory microclimate is modified by local factors (canopy closure but also forest structure and functional diversity), landscape features (topography, but also the proximity of a river or the degree of fragmentation of the surroundings) and climate change (notably increasing atmospheric CO2 and its effect on plant physiology and forest regeneration). To best tease apart the different factors influencing understory microclimate, we will integrate existing and comprehensive datasets of forest microclimate from Europe, North America and the Neotropical region, but will also design specific experiments or use biophysical microclimate models. Results from the project will then be synthetized and translated into clear recommendations and easy-to-use tools to help foresters understand the impact of climate change and their practices on understory microclimate. For example, our results should help us write an expertise report on the impact of forest management on the understory microclimate in riparian forest corridors. Two web tools dedicated to forest owners and managers, but also the general public, will be also developed: (1) an interactive virtual forest that will show how forest management can influence understory microclimate during specific past and future extreme events and; (2) a web “tracker” that will summarise, based on near real-time data, how understorey microclimate is buffered and decoupled from its macroclimate, for a set of typologies of forests or tree plantations in a given region. Other expected outcomes of the project are: new teaching materials (for forest engineering schools or master programmes, but also middle schools), new microclimate datasets, software updates and technical notes, as well as 8 master reports, 3 PhD theses and several peer-reviewed articles. The results of MaCCMic will be closely followed by the community of terrestrial ecologists interested in how climate change impacts forest biodiversity. These results should also strongly interest the global carbon cycle and climate change research community, by bringing new understanding of the biophysical and ecological mechanisms of forest regeneration and resilience under rising atmospheric CO2 concentrations. Our results on the impact of understory microclimate and atmospheric CO2 increase on forest regeneration and resilience should also interest strongly the research community working on the global carbon cycle and climate change. Finally, MaCCMic should have a strong impact on the forest sector by providing new tools to help forest managers increase the resilience of forests and foster their ecological, recreational and climate services in a warming world.

Trees play an essential role in the functioning of urban socio-ecosystems, providing vital ecosystem services for city dwellers. The diversity, size and distribution of trees in urban spaces reflect the socio-cultural dynamics of cities. Urban trees are vulnerable to environmental stresses and, as such, are sentinels of global change (heat, drought, soil artificialisation, erosion of biodiversity, introduction of species) as much as they represent a management lever for adapting cities to climate change. Understanding the factors that make urban trees vulnerable to biotic and abiotic stresses is essential if we are to manage the urban forest and sustainably drive the ecosystem services provided by trees to city dwellers. As the majority of urban trees are privately owned, urban forest management initiatives need to be a joint effort between municipal services and private individuals. This implies that all stakeholders share the same knowledge of the matter, the different management options and their consequences. It is therefore essential that scientific knowledge about turban tree health is accessible, understood and shared between the great diversity of stakeholders and citizen. OSCAR - the Scientific and Citizen Observatory of Urban Trees Hetalth - has this threefold ambition: (1) to co-construct scientific knowledge through the sponsorship of sentinel trees, (2) to encourage the dissemination of this knowledge in various forms so that (3) it can be appropriated by individuals and managers of green spaces and urban forests.

Theory predicts that virulence should be higher when multiple strains of parasites regularly compete within hosts. This is because, under conditions of multiple infection, parasites that exhaust limiting host resources more rapidly will leave more descendents than those that follow a more prudent strategy. Furthermore, plasticity of virulence expression, as well higher mean virulence, may evolve, allowing parasites to respond optimally to their local infection environment (i.e., multiple versus simple infection, relatedness of co-infecting strains…). Additional theoretical developments, however, suggest that the evolutionary trajectory of virulence as well as the value of optimal virulence under conditions of multiple infection will depend on the nature of within-host competition as well as on the degree of relatedness between interacting, competing parasites. For example, virulence is expected to decrease rather than increase under multiple infections in cases of interference (competitive inhibition) between different co-infecting parasites, particularly if parasite strains are unrelated. To date very few data are available with which to confront these theoretical predictions. In particular there are very few experiments that vary degree of genetic relatedness between strains of interacting or competing parasites. Here we propose a set of experiments in the field and the greenhouse using three different plant pathogen-host associations: Hyaloperonospora, an oomycete parasite of Arabidopsis thaliana, Microbotryum, a basidiomycete anther smut of the Caryophyllaceae, and Cryphonectria parasitica, the chestnut blight fungus, that itself is parasitized by a double stranded hypovirulence virus. All three are model systems for which a battery of genetic tools are rapidly becoming available, but more importantly, all present multiple infections in natural populations and all are well suited to this kind of experimental manipulation. We will perform experimental inoculations of multiple parasite strains and measure the response in terms of virulence. We will also follow the course of multiple infections to determine whether parasite strains can coexist, can do so in a perennial fashion or whether one strain can exclude the other, and whether this depend on relatedness between them. We will measure the phenotypic effect of single versus multiple infections, and in particular of multiple infections that vary for the degree of genetic relatedness between co-infecting parasite strains to determine whether parasites exhibit plasticity for the negative effects on their hosts and are sensitive to the kin status of their competitors. This is timely because the role of kin selection in the evolution of social behaviour in general and costly parasite traits that can cause damage to hosts is currently the object of some controversy. We intend to contribute to this debate in an informed manner, by providing data on how kin versus non-kin parasites interact when they compete for host resources. Despite the breadth of the biological details of our systems, most of our questions are general to all three. This work should elucidate the effects of within-host competition between more or less related parasite strains on how damaging parasites are to their hosts. Our results will aid in designing control programmes that take into consideration the long-term effects of modifying the competitive environment of parasites and the identity of likely competitors. Our project proposes basic research that nonetheless has important applications for better design of informed parasite control programmes that are of extreme importance for human health, food security and management of forests.

Tropical grassy biomes (TGB), the world’s ancient savannas and grasslands, support outstanding biodiversity, and provide key ecosystem processes. Our goal is to understand the functional mechanisms promoting the restoration of native herbaceous TGB communities that are fire-resilient, self-sustaining, invasion-resistant, and able to provide crucial ecosystem processes. We choose the Cerrado (Brazilian savanna) as a model to answer our research questions as it hosts a vast biodiversity, offers many ecosystem services and is currently highly threatened. We will set up a Biodiversity-and-Ecosystem-Functioning field experiment to understand how the manipulation of both functional diversity and species richness of herbaceous plants allow the establishment of a continuous herbaceous ground cover. We aim at better understanding how functional diversity and species richness modulate restored ecosystem functioning. Current restoration of Cerrado herbaceous communities rely on direct seeding of fast-growing, acquisitive species, whereas we will develop methods that allow establishing a range of species, including species with conservative strategies, characteristics of pristine TGB. Yr1: collect seeds and propagules from 4 functional groups; set up field experiment. Yr2-4: monitor vegetation (establishment, plant functional traits, invasive species, flammability) and ecosystem processes (erosion control, productivity, carbon and water cycles). Test, in mesocosms, if the response of the functional groups to invasive species is modified by extreme weather events. Yr3: set prescribed fires. Yr4: monitor recovery. We expect to find a positive correlation between the complementarity of functional traits and restoration effectiveness. This project will contribute to deepening TGB ecological knowledge and to informing guidelines for effective TGB restoration. Partnerships with stakeholders and local traditional Kalunga communities should improve these guidelines.

Trees are an important component of the biosphere. They dominate many regions of the world as natural forests or plantations. They are not only important economically through the multiple uses of wood, but also for climate change mitigation through their function as carbon dioxide sinks, as well as for their role in the regulation of the hydrological cycle. Recent studies on tree mortality and climate change show that some of the world's forest ecosystems may already be responding with increasing tree mortality rates, in response to climatic warming and drought, even in environments that are not normally considered water-limited. In the long term, growth and survival of trees largely depend on their ability to adapt to the predicted rapid climatic changes. Among the possible strategies for adapting forests to climate change, the optimal use of natural genetic variation certainly represents an important component, along with genetic improvement, forest management and facilitation of migration. A sustainable management of forest ecosystems will require an understanding of the processes underlying adaptation to climate change. Knowledge of processes, and finally genes, involved in the variation of traits affecting fitness, the assessment of their variability in natural tree populations and their use as an indicator of adaptability should improve management practices facing climate change. An important management goal, in the context of climate change, is to optimize biomass growth versus water used through transpiration, even in forests that are presently only exposed to moderate soil water deficits. The ratio between these two traits is called the water use efficiency (WUE). Recent modelling studies, based on plastic responses of ecophysiological traits, have shown that predicted climatic changes will impact the WUE of forest ecosystems. The H2Oak project focuses on the diversity of WUE in two major French oak species : Quercus robur (pedunculate oak) and Q. petraea (sessile oak). In France they represent 11% of the total timber harvested and one fourth of the total forested area (~4Mha). These two species are largely sympatric, but have different ecological requirements: Q. petraea is more frequently found on well drained soils and is more tolerant to drought, whereas Q. robur is able to survive and grow on poorly drained sites and displays a higher tolerance to water-logging. Q. petraea has a higher WUE compared to Q. robur. Such an eco-hydrological niche segregation has been suggested to have implications for conservation in habitats that face changing water constraints caused by climate change. The main objective of the H2Oak project is to determine whether WUE and underlying traits play an adaptive role in oaks in terms of (i) impact on tree fitness, (ii) past selection and adaptation of provenances to their specific environments, and (iii) sufficient standing genetic diversity for future adaptation related to climate change, especially increased soil water deficit. The ultimate goal is to define genetic factors that can be used to evaluate the impact of silviculture and forest management practices on the adaptive potential of efficient use of water in oak forests. The proposed project will take a large step towards the discovery of genes underlying the ecological divergence within these oak species using forward genetics approaches (including QTL and association mapping), and ecological genomics. The H2Oak project will follow a progression of tasks advancing from detailing the genomic regions related to WUE in known progenies, using extreme phenotypes to refine diversity of physiological responses, screening candidate genes in diversity panels based on geographic distribution of populations, and applying the discovered adaptive molecular markers to study adaptation in natural regenerations of oak seedlings under silvicultural management.