J. For. Sci., 2026, 72(9):483-499 | DOI: 10.17221/61/2026-JFS

Cross-scale assessment of pigment differences between healthy and bark-beetle-damaged Norway spruce stands using UAV and airborne hyperspectral imageryOriginal Paper

Adenan Yandra Nofrizal ORCID...¹, Lucie Červená ORCID...¹, Jakub Lysák ORCID...¹, Zuzana Lhotáková ORCID...², Kristýna Štěpánová², Jana Albrechtová ORCID...², Lucie Kupková ORCID...¹

¹ Department of Applied Geoinformatics and Cartography, Faculty of Science, Charles University in Prague, Prague, Czech Republic

² Department of Experimental Plant Biology, Faculty of Science, Charles University in Prague, Prague, Czech Republic

Chlorophyll and carotenoid content provide information on forest canopy condition and may reveal biochemical differences associated with disturbance. However, it remains uncertain whether these differences can be consistently detected from hyperspectral observations acquired at different spatial scales. We assessed pigment differences between two contrasting Norway spruce [Picea abies (L.) Karst.] reference stands: one without visible crown damage and one disturbed following bark beetle infestation in Krkonoše National Park, Czechia. The study combined 54 biochemical needle samples from 18 trees and simultaneous UAV Headwall Nano-Hyperspec® and airborne CASI-1500 imagery. A hybrid framework based on PROSAIL simulations and Random Forest regression was used to retrieve chlorophyll and carotenoid content. After averaging the three within-tree image-derived estimates to obtain one crown-level value per tree, linear models based on 18 independent crown-level observations showed higher retrieved chlorophyll and carotenoid content at Tetřeví Boudy (healthy) than at Rejdiště (infested). UAV retrieval achieved R² = 0.96 and RMSE (root mean square error) = 2.64 µg·cm^–2 for chlorophyll and R² = 0.80 and RMSE = 0.9 µg·cm^–2 for carotenoids. Airborne retrievals reached R² = 0.93 and RMSE = 3.76 µg·cm^–2 for chlorophyll and R² = 0.76 and RMSE = 0.95 µg·cm^–2 for carotenoids. Chlorophyll showed stronger cross-scale correlation than carotenoids (r = 0.98 and 0.89, respectively), while the main spatial patterns and differences between stands were preserved at both scales. The results provide proof of concept that physiologically meaningful pigment differences between contrasting Norway spruce stands can be captured using UAV and airborne hyperspectral data. Because only two stands and one acquisition date were analysed, although the single-stand-per-condition design precludes attribution of the contrast to bark beetle damage, and broader validation across stands, disturbance stages and seasons is required.

Keywords: carotenoids; chlorophyll; forest health; imaging spectroscopy; PROSAIL

Received: August 8, 2026; Revised: September 23, 2026; Accepted: September 24, 2026; Published: September 30, 2026  Show citation