SUPERVISOR: Christine STUMPP

PROJECT ASSIGNED TO: Megan ASANZA-GRABENBAUER

Due to climate change, droughts and precipitation increase in severity (IPCC, 2023). In Austria, precipitation is expected to increase during winter and spring, while moderate and extreme summer droughts become more frequent (Haslinger et al., 2023). This poses significant risks to forest ecosystems and drought sensitive tree species like the European beech (Fagus sylvatica S.). The interactions between forests and the water cycle during droughts, including impacts on evapotranspiration or stream water quality and quantity, are not fully understood yet, necessitating better knowledge to mitigate future drought-related water deficits in Austria (Jones et al., 2020). Therefore, this project aims to investigate how resilient beech trees are to prolonged droughts and extreme rainfall. Under normal conditions and through manipulation experiments, this research aims to:

(1) elucidate whether beech trees rely more on winter or summer rainfall for their water needs, (2) estimate evapotranspiration and partition it into evaporation and transpiration, and

(3) estimate groundwater recharge.

Drought will be simulated with rainout shelters, while high‑intensity rainfall will be generated using sprinklers at a mature beech stand in the Rosalia Forest, Austria. High-resolution measurements of soil and xylem water isotopes will be achieved by installing gas-permeable probes into the soil and sapwood, which will continuously deliver soil and xylem water vapor for laser spectroscopic analysis in the field. Field monitoring includes a metrological station with a precipitation autosampler, soil moisture and temperature sensors, and tensiometers. In addition to in-situ sampling, soil cores are collected every 3 weeks from January 2025 to April 2027, while xylem cores are only collected during the growing seasons. These samples are analyzed in the laboratory together with precipitation collected by the autosampler. Stable water isotopes will be used to quantify the seasonal origin of tree water with the seasonal origin index (Allen et al., 2019) and to estimate evaporation and transpiration rates using a water and isotope mass balance approach (Liebhard et al., 2022). Groundwater recharge will be assessed with the isotope‑based piston displacement method (Allison & Hughes, 1983) in combination with HYDRUS‑1D modeling (J. et al., 1998).

This project aims to provide a comprehensive understanding on how beech trees in the Rosalia Forest respond to drought and intense rainfall. By quantifying changes in water fluxes under these conditions, this research will offer valuable insights into the hydrological processes that support beech tree resilience. Furthermore, this project will develop a non-destructive method to achieve high-resolution data. These findings will be applicable to other forests in similar hydroclimatic regions and will guide forest management practices in enhancing health and sustainability of beech forests amid climate change. This study expands the research topic of HR21 on water resources under the vulnerability, metabolism and connectivity research clusters.

 

Allen, S. T., Kirchner, J. W., Braun, S., Siegwolf, R. T. W., & Goldsmith, G. R. (2019). Seasonal origins of soil water used by trees. Hydrology and Earth System Sciences, 23(2), 1199-1210. https://doi.org/10.5194/HESS-23-1199-2019

Allison, G. B., & Hughes, M. W. (1983). The use of natural tracers as indicators of soil-water movement in a temperate semi-arid region. Journal of Hydrology, 60(1-4). https://doi.org/10.1016/0022-1694(83)90019-7

Haslinger, K., Schöner, W., Abermann, J., Laaha, G., Andre, K., Olefs, M., & Koch, R. (2023). Apparent contradiction in the projected climatic water balance for Austria: wetter conditions on average versus higher probability of meteorological droughts. Natural Hazards and Earth System Sciences, 23(8), 2749-2768. https://doi.org/10.5194/NHESS-23-2749-2023

IPCC. (2023). Climate Change 2023: Synthesis Report (Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)], Issue. IPCC. doi.org/10.59327/IPCC/AR6-9789291691647

J., Š., M., Š., M.T., V. G., D., J., D., M., H., S., & M., S. (1998). The Hydrus-1D software package for simulating the one-dimensional movement of water, heat, and multiple solutes in variably-saturated media (IGWMC – TPS – 70). C. S. o. M. International Ground Water Modeling Center. 

Jones, J. A., Wei, X., Archer, E., Bishop, K., Blanco, J. A., Ellison, D.,…Creed, I. F. (2020). Forest-Water Interactions Under Global Change. 589-624. https://doi.org/10.1007/978-3-030-26086-6_24

Liebhard, Klik, A., Stumpp, C., & Nolz, R. (2022). Partitioning evapotranspiration using water stable isotopes and information from lysimeter experiments. Hydrological Sciences Journal, 67(4), 646-661.