Format: ORAL

Ral Garca-Valds 1; José V. Roces-Díaz 2,3,4; Miquel de Cáceres 2; Adrià Descals 2; Pilar Hurtado 2; Francisco Lloret 2,5; Josep Maria Espelta 2; Jose Manuel Álvarez-Martínez 6; Enric Batllori Presas 7; Jordi Martínez-Vilalta 2,5

1. Department of Biology, Geology, Physics and Inorganic Chemistry, School of Experimental Sciences and Technology, Rey Juan Carlos University, E28933 Móstoles, Madrid, Spain 2. CREAF, E08193 Bellaterra (Cerdanyola del Vallès), Catalonia, Spain 3. Smart-Forests Research Group, Department of Organisms and Systems Biology, University of Oviedo, Campus de Mieres C/ Gonzalo Gutiérrez Quirós s/n, 33600 Mieres, España. 4. Biodiversity Research Institute IMIB, Spanish Research Council CSIC – University of Oviedo – Principado de Asturias, C/ Gonzalo Gutiérrez Quirós s/n, 33600 Mieres, España 5. Universitat Autònoma de Barcelona, E08193 Bellaterra (Cerdanyola del Vallès), Catalonia, Spain 6. Environmental Hydraulics Institute “IH Cantabria”, University of Cantabria, PCTCAN. C/ Isabel Torres 15, 39011 Santander, Spain 7. Departament de Biologia Evolutiva, Ecologia i Ciències Ambientals, Facultat de Biologia, Universitat de Barcelona (UB), Av. Diagonal 645, Barcelona 08028, Spain.

Forest biomass productivity is essential for climate functioning and for providing other services to humankind. This productivity, however, is not constant, and it fluctuates between years due to variations in climate and the intrinsic characteristics of tree communities. At the same time, climate change is rising temperatures and climate variability around the World, increasing forest vulnerability to drought, and compromising the stability of forest functioning and services. It is therefore important to understand what factors drive the stability in forest productivity. We explored how tree community characteristics (local climate, vegetation structure and drought-related traits) affected the stability of 40k permanent forest plots across Spain. We used two decades of productivity-related satellite indices (NDVI and EVI) for measuring forest productivity stability, and stand-level data derived from the Spanish National Forest Inventory for measuring tree community structure (maturity and tree density) and mean and diversity of hydraulic drought tolerance traits (P50 and HSM). We found that there are complex interactions determining the patterns of stability, including direct and indirect effects of environmental variables, vegetation structure and tree species drought adaptations. Forests showed higher stability with higher water availability, its stability in time, stand development and density of trees. We also found solid evidence that tree community diversity in hydraulic drought tolerance favoured stability. Results indicated that this diversity influences both, the mean of productivity (positively) and its standard deviation (negatively). Mean drought tolerance at the community level showed a less clear (but mostly negative) effect on stability. These results suggest that drought-related functional diversification would be a good management strategy to secure the stable provision of forest ecosystem services, especially under increasing variability in climate and intensity of droughts.