Similar tree species richness-productivity response but differing effectson carbon stocks and timber production in eastern US andcontinental Spain

Unimodal response of tree species richness to increases in aboveground productivity is evident in grasslands butto a lesser extent in forests, where confounding factors (e.g., abiotic factors and management regimes) may alterthe response and compromise the delivery of ecosystem services. We hypothesize that unimodalresponse of bio-mass accumulation through increased species richness leads to greater tree above ground carbon (AGC) stocksand thus climate regulation but not necessarily higher timber volume production for human consumption acrossportions of North American and European forests. Wefirst evaluated the biodiversity-productivity pattern andassessed if the addition of potential confounding variables altered the response. Afterwards, we integrated directand indirect effects of species richness and confounding factors in the modelling of aboveground carbon stockand timber volume. We confirm an increase in carbon stocks concomitant with an increase in tree species rich-ness up to an optimum biomass value in both regions. Tree species richness had a marginal effect on both above-groundcarbonstocks and timber volumewitha trade-offinthe easternUS. Biomassaccumulation islower intreeplantations than in natural forests, although volume increased with species richness. Naturally-regenerated for-ests needed as much as double the number of tree species than plantations to reach the same carbon stocks. Dis-tinct ecosystem services (AGC and timber volume) showed unique pathways of achieving their maximumprovisioning. As increasing forest resilience to global change requires a fundamental understanding of howtree species combine with changing climatic conditions to drive the provisioning of various ecosystem services,further examination of this study'sfindings across additional biogeographical regions may lead the way tounraveling such dynamics and empowering adaptive management.We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe