Summary• The variability of branch-level hydraulic properties was assessed across 12 Scots pine populations covering a wide range of environmental conditions, including some of the southernmost populations of the species. The aims were to relate this variability to differences in climate, and to study the potential tradeoffs between traits.• Traits measured included wood density, radial growth, xylem anatomy, sapwoodand leaf-specific hydraulic conductivity (K S and K L ), vulnerability to embolism, leaf-to-sapwood area ratio (A L : A S ), needle carbon isotope discrimination (Δ 13 C) and nitrogen content, and specific leaf area.• Between-population variability was high for most of the hydraulic traits studied, but it was directly associated with climate dryness (defined as a combination of atmospheric moisture demand and availability) only for A L : A S , K L and Δ 13 C. Shoot radial growth and A L : A S declined with stand development, which is consistent with a strategy to avoid exceedingly low water potentials as tree size increases. In addition, we did not find evidence at the intraspecific level of some associations between hydraulic traits that have been commonly reported across species.• The adjustment of Scots pine's hydraulic system to local climatic conditions occurred primarily through modifications of A L : A S and direct stomatal control, whereas intraspecific variation in vulnerability to embolism and leaf physiology appears to be limited.

According to the competitive exclusion principle, species with low competitive abilities should be excluded by more efficient competitors, and yet they generally remain as rare species. Here, we describe the positive and negative spatial association networks of 326 disparate assemblages, showing a general organization pattern that simultaneously supports the primacy of competition and the persistence of rare species. Abundant species monopolize negative associations in about 90% of the assemblages. Contrarily, rare species are mostly involved in positive associations, forming small network modules. Simulations suggest that positive interactions among rare species and microhabitat preferences are the most likely mechanisms underpinning this pattern and rare species persistence. The

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

Summary1. Plants exhibit a wide variety in traits at different organizational levels. Intraspecific and interspecific studies have potential to demonstrate functional relationships and trade-offs amongst traits, with potential consequences for growth. However, the distinction between the correlative and functional nature of trait covariation presents a challenge because traits interact in complex ways. 2. We present an intraspecific study on Scots pine branches and use functional multi-trait concepts to organize and understand trait interactions and their impacts on growth. Branch-level traits were assessed for 97 branches from 12 Scots pine sites across Europe. 3. To test alternative hypotheses on cause-effect relationships between anatomical traits, hydraulic traits and branch growth, we measured for each branch: the tracheid hydraulic diameter, double cell wall thickness, cell lumen span area, wood density, cavitation vulnerability, wood-specific hydraulic conductivity, the leaf area to sapwood area ratio and branch growth. We used mixed linear effect models and path models to show how anatomical traits determine hydraulic traits and, in turn, how those traits influence growth. 4. Tracheid hydraulic diameter was the best predictor of cavitation vulnerability (R 2 = 0AE09 explained by path model) and specific conductivity (R 2 = 0AE19) amongst anatomical traits. Leaf area to sapwood area ratio had the strongest direct effect on branch growth (R 2 = 0AE19) and was positively associated with the tracheid hydraulic diameter (R 2 = 0AE22). A number of bivariate correlations between traits could be explained by these functional relationships amongst traits. 5. The plasticity in tracheid hydraulic diameter (10.0-15.1 lm) and leaf area to sapwood area ratio (600-6051 cm 2 cm )2 ) and the maintenance of a minimum leaf water potential (between )2 and )2AE5 MPa) appear to drive the anatomical and hydraulic traits of Scots pine across Europe. These properties are major drivers of the functional trait network underlying the growth variation amongst pine branches and thus possibly contribute to the ecological success of pines at a local and continental scale.

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