Environmental controls on canopy phenolics in European temperate forests revealed with spaceborne imaging spectroscopy

Understanding the spatial variability of canopy biochemistry is increasingly important for quantifying forest functional diversity, monitoring ecosystem resilience, and assessing biodiversity change. Canopy phenolics–such as total phenols and tannins–are key biochemical traits linked to plant defences, decomposition processes, and nutrient cycling. Although imaging spectroscopy has recently proven effective for estimating canopy phenolics, the environmental drivers shaping their large-scale variation remain poorly understood. In this study, we used PRecursore IperSpettrale della Missione Applicativa (PRISMA) hyperspectral imagery to map canopy total phenol content across temperate forests in the central Netherlands and southeastern Germany. Specifically, we investigated how climatic, topographic, and edaphic factors shape the spatial distribution of canopy phenolics. First, a nested permutational partial least squares regression (PLSR) was implemented to calibrate PRISMA reflectance (450–2400 nm) against in situ canopy phenol measurements, producing accurate and robust retrievals (R² = 0.64; normalized RMSE = 12.7%). The validated model was then applied to generate phenol maps that successfully captured fine-scale variability across diverse species compositions and forest structures with low prediction uncertainty. Finally, we used random forest modelling and variance partitioning to identify dominant environmental drivers and quantify the explained variation in canopy phenolics. Our results show that regional phenolic variation is primarily driven by edaphic variables, particularly within conifer-dominated forest landscapes. In deciduous and mixed forests, topographic and climatic influences become more pronounced, highlighting species- and context-dependent phenolic–environment relationships. By linking EO-derived phenolics with spatial environmental gradients, this study demonstrates how imaging spectroscopy can move beyond trait mapping toward a more mechanistic understanding of ecosystem functioning. These findings are relevant to understanding European temperate forest responses to climate variability and environmental changes. Canopy phenolics retrieved from space can also serve as scalable indicators of plant defence strategies, ecosystem resilience, and biodiversity–function relationships, supporting sustainable forest management and national reporting under the Kunming–Montréal Global Biodiversity Framework.