Neue Publikation - Gräf et al. 2025

Michael Gräf, Peter Hietz, Rosemarie Stangl, Maximilian Poiss, Guido D’Urso, Stefan Lederbauer, Markus Immitzer

10.09.2025

https://academic.oup.com/forestry/advance-article/doi/10.1093/forestry/cpaf056/8250587

Abstract

Climate change forecasts for Central Europe predict increased drought and reduced summer precipitation, potentially endangering established forest ecosystems. Reliable detection of drought-stressed forests could be helpful to plan and initiate mitigation measures. This study evaluates the effectiveness of thermal infrared imaging in detecting drought stress in coniferous species, Picea abies (Norway spruce) and Abies alba (Silver fir), under controlled conditions. We conducted a 45-day experiment in a controlled environment using low-cost, high-resolution thermal cameras to monitor differences in leaf surface temperatures (T_DIFF) of drought-stressed and well-watered potted plants. We also measured transpiration rates using weight cells to understand the link between leaf temperature and water loss. Our findings indicate that drought stress is detectable 17–25 days earlier in the thermal infrared than through visual symptoms, such as leaf desiccation. For A. alba, T_DIFF increased significantly by Day 9 of drought stress imposition, while for P. abies, the first signs appeared at Day 13. Maximum mean T_DIFF values reached up to 1.5°C for A. alba and P. abies, demonstrating a clear thermal response to drought stress. The correlation between decreasing transpiration rates and increasing T_DIFF highlights the utility of thermal infrared imaging for the early detection of drought stress in coniferous species. This research supports the potential of thermal infrared imaging for monitoring plant water stress while noting the challenges of controlling environmental variables in practice.