Water and carbon fluxes in forests are largely related to leaf gas exchange physiology 27 varying across spatiotemporal scales and modulated by plant responses to environmental cues. 28 We quantified the relevance of genetic and phenotypic variation of intrinsic water-use 29 efficiency (WUEi, ratio of net photosynthesis to stomatal conductance of water) in Pinus 30 sylvestris L. growing in the Iberian Peninsula as inferred from tree-ring carbon isotopes. Inter-31 population genetic variation, evaluated in a provenance trial comprising Spanish and German 32 populations, was low and relevant only at continental scale. In contrast, phenotypic variation, 33 evaluated in natural stands (at spatial level) and by tree-ring chronologies (at temporal inter-34 annual level), was important and ten-and threefold larger than the population genetic 35 variance, respectively. These results points to preponderance of plastic responses dominating 36 variability in WUEi for this species. Spatial phenotypic variation in WUEi correlated 37 negatively with soil depth (r=-0.66; p<0.01), while temporal phenotypic variation was mainly 38 driven by summer precipitation. At the spatial level, WUEi could be scaled-up to ecosystem-39 level WUE derived from remote sensing data by accounting for soil water holding capacity 40 (r= 0.63; p<0.01). This outcome demonstrates a direct influence of the variation of leaf-level 41 WUEi on ecosystem water and carbon balance differentiation. Our findings highlight the 42 contrasting importance of genetic variation (negligible) and plastic responses in WUEi (large, 43 with changes of up to 33% among sites) on determining carbon and water budgets at stand 44 and ecosystem scales in a widespread conifer such as Pinus sylvestris.

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Aim of the study: To develop regional guidelines for sustainable forest management.Area of the study: Forests of Catalonia (NE Spain).Material and methods: The process of developing the forest management guidelines (FMG) started by establishing a thorough classification of forest types at stand level. This classification hinges on two attributes: tree species composition and site quality based on ecological variables, which together determine potential productivity. From there, the management guidelines establish certain objectives and silvicultural models for each forest type. The forest type classifications, like the silvicultural models, were produced using both existing and newly-built growth models based on data from the National Forest Inventory (NFI) and expert knowledge. The effort involved over 20 expert working groups in order to better integrate the expertise and vision of different sectorial agents.Main results: The FMG consist in quantitative silvicultural models that include typical silvicultural variables, technical descriptions of treatments and codes of good practice. Guidelines now cover almost all forest types in Catalonia (spanning up to 90% of the Catalan forest area). Different silvicultural models have been developed for pure and mixed stands, different site quality classes (2–3 classes per species), and even- and multi-aged stands.Research highlights: FMG: i) orient the management of private and public forests, (ii) provide a technical scaffold for efficient allocation/investment of public subsidies in forest management, and (iii) bridge forest planning instruments at regional (strategic-tactical) and stand (operational) level.

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