DOI: 10.17863/cam.57197
title: Datasets and scripts used for the publication "Direct response of tree growth to soil water and its implications for terrestrial carbon cycle modelling"

description: This Dataset contains all data files and scripts necessary to replicate the analysis in the linked publication. The project was conducted as part of the Dissertation by the first author. Field data has been collected in Switzerland. A README file contains a description of all files and how they are generated or used in the analysis. Field data generation was funded by the Swiss National science foundation (projects INTEGRAL-121859, LOTFOR-150205, and CLIMWOOD-160077): TRW data have been included in Peters et al. 2017. The soil moisture was originally used in Peters et al. 2019 and the xylogenesis data in Cuny et al 2019. ABSTRACT of the publication: Wood growth constitutes the main process for long-term atmospheric C sequestration in vegetation. However, our understanding of the process of wood growth and its response to environmental drivers is limited. Current Dynamic Global Vegetation Models (DGVMs) are mainly photosynthesis-driven and thus do not explicitly include a direct environmental effect on tree growth. However, physiological evidence suggests that, to realistically model vegetation carbon allocation under increased climatic stressors, it is crucial to treat growth responses independently from photosynthesis. A plausible growth response suitable for global simulations in DGVMs has been lacking. Here, we present the first soil water-growth response function and parameter range for Larch and Spruce in a dry temperate forest, tested and parameterised at a site in a valley in the Swiss Alps. We present a new data-driven approach based on a combination of tree ring width records, growing season length and simulated sub-daily soil hydrology to parameterise ring width increment simulations. We found that a simple linear function, with an intercept at zero moisture stress, could explain up to 62.3% and 59.4% of observed tree ring widths for Larch and Spruce respectively and, importantly, the slope was much steeper than literature values for the effect of soil moisture on photosynthesis or stomatal conductance. For example, we found tree stem growth stops at a soil moisture potential of -0.47 MPa for Larch and -0.66 MPa for Spruce, whereas photosynthesis in trees stops at -1.2 MPa or later, depending on species and measurement method. These results are strong evidence that the response functions of source and sink processes are indeed very different in trees, and need to be considered separately to correctly assess vegetation responses to environmental change. Our results provide a parameterisation for the explicit representation of growth responses to soil water in vegetation models. Peters, R. L., Klesse, S., Fonti, P., & Frank, D. C. (2017). Contribution of climate vs. Larch budmoth outbreaks in regulating biomass accumulation in high-elevation forests. Forest Ecology and Management, 401, 147–158. https://doi.org/10.1016/j.foreco.2017.06.032 Peters, R. L., Speich, M., Pappas, C., Kahmen, A., Arx, G. von, Pannatier, E. G., Steppe, K., Treydte, K., Stritih, A., & Fonti, P. (2019). Contrasting stomatal sensitivity to temperature and soil drought in mature alpine conifers. Plant, Cell & Environment, 42(5), 1674–1689. https://doi.org/10.1111/pce.13500 Peters, R. L., Speich, M., Pappas, C., Kahmen, A., Arx, G. von, Pannatier, E. G., Steppe, K., Treydte, K., Stritih, A., & Fonti, P. (2019). Contrasting stomatal sensitivity to temperature and soil drought in mature alpine conifers. Plant, Cell & Environment, 42(5), 1674–1689. https://doi.org/10.1111/pce.13500