Les objectifs de ce projet étaient de décrire et quantifier les processus de croissance primaire aérienne du pin d'Alep et d'évaluer leur relation avec le climat. La croissance primaire (allongement des branches, taux de ramification, polycyclisme, nombre et atille d'aiguilles, fructification) c'est à dire le développement architectural du houppier et la fructification, ont été reconstitués pour les 16 dernières années en région méditerranéenne française. De 1998 à 2007, le climat de la zone d'étude a été beaucoup plus chaud et sec que la normale. Toutes les variables relatives au développement du houppier et la fructification, de même que la croissance en diamètre, ont décliné significativement après la canicule de 2003 et durant les années de sécheresses répétées qui ont suivi de 2004 à 2007. Une reprise partielle a été observée de 2008 à 2010 sur les branches vigoureuses, tandis que les branches faibles montraient moins d'amélioration. Le développement limité du houppier durant les années défavorables réduit significativement le potentiel photosynthétique des arbres durant plusieurs années suivantes et contribue à une convalescence plus longue que prévue ou à la mort différée des arbres. / The objectives of this study were to describe and quantify Aleppo pine aerial primary growth processes and to assess their relationships with climate. Primary growth (branch length growth, branching rate, polycyclism, needle number and size, fruiting), i.e. crown development and reproduction, was reconstructed for the last 16 years in Mediterranean France. From 1998 to 2007, climate has been far hotter and drier than normal in South-eastern France. All variables related to crown development and fruiting, as well as radial growth, significantly declined after 2003 heat-wave and during repeated droughts from 2004 to 2007. A partial recovery of most parameters occurred from 2008 to 2010 on vigorous branches while frail branches showed less improvement. The limited crown development during unfavourable years may significantly hold back tree potential photosynthetic biomass for several following years and contribute to a slower than expected recovery of tree growth or to delayed die-back

1Due to the scarcity of reliable and highly resolved moisture proxies covering much of the 2 Holocene, there has been increased interest in the study of living and subfossil peatland trees 3 sensitive to gradual and extreme changes in hydrology, precipitation, and related environmental 4 processes. Peatland development and the associated carbon accumulation, which are strongly 5 influenced by hydrological fluctuations, are also of prime importance as peatlands represent long-6 term sinks of atmospheric carbon. Improved knowledge of peatland development and soil 7 moisture variability during the Holocene is therefore essential to our understanding of long-term 8 hydroclimate changes, the terrestrial carbon cycle, and to enable more robust predictions of 9 peatland response to future climate changes. 10Here, we review the existing mid-to late Holocene peatland tree-ring chronologies that 11 have been used to study climate variability on (sub-)annual to centennial scales with a primary 12 focus on northern Europe. Since the 1970s, absolutely dated tree-ring chronologies covering 13 substantial parts of the Holocene have been developed from excavated remains of oak (Quercus 14 spp.) and pine (Pinus sylvestris L.). The annual tree-ring patterns of these trees are often 15 characterized by periods of depressed growth reflecting annual to decadal hydroclimatic changes. 16In addition, changes in the spatio-temporal distribution of trees throughout the Holocene are often 17 found to reflect decadal to centennial climate and hydrological changes. Moreover, synchronicity 18 between tree-ring chronologies and tree-population dynamics over larger geographical areas 19 show periods of coherent regional climate forcing, especially during the mid-Holocene. 20This review (i) provides an overview of pioneering and recent studies presenting tree-ring 21 chronologies developed from subfossil peatland trees, and (ii) presents recent developments in the 22 fields of dendroecology (i.e. the response of tree growth and changes in vitality as a result of 23 changes in climatic variables) and dendroclimatology (i.e. the reconstruction of climate 24 4 fluctuations based on tree-ring analyses) in peatland regions. Moreover, we (iii) use long-term 25 climate reconstructions based on alternative proxies for comparison, and (iv) present different 26 ways to analyse tree-ring records to generate novel information on annual to centennial 27 timescales. This analysis is based on an unprecedented network of tree-ring chronologies from 28 Denmark, Finland, Germany, Great Britain, Ireland, Lithuania, the Netherlands, Poland, Sweden, 29and Canada, as well as a wealth of old and previously (un) published literature from Scandinavia 30 and Germany, which has not been accessible to a wider audience in the past due to inaccessibility 31 or linguistic barriers. Finally, a map of possible hotspots for the assessment of continuous 32 peatland-tree studies is presented, along with suggestions for new research directions in the field. 33 34

Enhanced shrub growth in a warming alpine climate has potential far-reaching implications, including soil nutrient cycling, carbon storage, or water and surface energy exchanges. Growth ring analysis can yield mid-to long-term, annually resolved records of shrub growth, and thereby offer valuable insights into how growth is driven by interannual climate variability. In the European Alps, dendroecological approaches have shown that dwarf shrub productivity is influenced by interannual variations of growing season temperature but results also point to a negative effect of winter precipitation on radial growth. However, as past work lacked snow cover data, links between snow cover duration, growing season length, energy availability and inter-annual shrub growth remain poorly understood. In this paper, we combined multi-decadal shrub-ring series from 49 individuals sampled at three sites along a 600-m elevational gradient in the Taillefer massif, located in the French Alps to assess growth sensitivity of long-lived and widespread Rhododendron ferrugineum shrubs to 2 both snow cover dynamics and temperature changes. To this end, we computed structural equation models to track the response of shrub radial growth to extending growing season at 1800, 2000 and 2400 m above sea level and for two time periods (i.e. 1959-1988 and 1989-2016). The second period is marked by a significant advance in snow melt-out resulting in a regime shift highlighted at the end of the 1980s by a breakpoint analysis. At the high-elevation site, our results demonstrate a positive effect of increasing growing season length on shrub growth, which is strongly dependent on snowpack depth and snow cover duration. Conversely, at lower elevations, earlier melt-out dates and associated late frost exposure are shown to lead to radial growth reduction. Moreover, the climate signal in ringwidth chronologies of R. ferrugineum portrays a weakening since 1988similar to a phenomenon observed in series from circumpolar and alpine tree-ring sites and referred to as "divergence". By analyzing long-term records of radial growth along an elevation gradient, our work provides novel insights into the complex responses of shrub growth to climate change in alpine environments. This paper demonstrates that R. ferrugineum, as a dominant alpine shrub species, behave as an ecological indicator of the response of alpine ecosystem to global warming.