Manuel Nicolas, Duccio Rocchini, Fabian Ewald Fassnacht, Raf Aerts, Michael Ewald, Ben Somers, Olivier Honnay, Hannes Feilhauer, Sebastian Schmidtlein, Sandra Skowronek, Jonathan Lenoir, Tarek Hattab, Jérôme Piat, Ruben Van De Kerchove, Carol X. Garzon-Lopez, Ecologie et Dynamique des Systèmes Anthropisés - UMR CNRS 7058 (EDYSAN), Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS), R&D, Astra Zenec, Université Catholique de Louvain = Catholic University of Louvain (UCL), Catholic University of Leuven - Katholieke Universiteit Leuven (KU Leuven), Ecosystèmes et Ressources Aquatiques (UR03AGRO1), Institut National Agronomique de Tunisie, MARine Biodiversity Exploitation and Conservation (UMR MARBEC), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Karlsruhe Institute of Technology (KIT), Centre National de la Recherche Scientifique (CNRS)-Université de Picardie Jules Verne (UPJV), Ewald, Michael, Aerts, Raf, Lenoir, Jonathan, Fassnacht, Fabian Ewald, Nicolas, Manuel, Skowronek, Sandra, Piat, Jérôme, Honnay, Olivier, Garzón-López, Carol Ximena, Feilhauer, Hanne, Van De Kerchove, Ruben, Somers, Ben, Hattab, Tarek, Rocchini, Duccio, and Schmidtlein, Sebastian
Imaging spectroscopy is a powerful tool for mapping chemical leaf traits at the canopy level. However, covariance with structural canopy properties is hampering the ability to predict leaf biochemical traits in structurally heterogeneous forests. Here, we used imaging spectroscopy data to map canopy level leaf nitrogen (Nₘₐₛₛ) and phosphorus concentrations (Pₘₐₛₛ) of a temperate mixed forest. By integrating predictor variables derived from airborne laser scanning (LiDAR), capturing the biophysical complexity of the canopy, we aimed at improving predictions of Nₘₐₛₛ and Pₘₐₛₛ. We used partial least squares regression (PLSR) models to link community weighted means of both leaf constituents with 245 hyperspectral bands (426–2425 nm) and 38 LiDAR-derived variables. LiDAR-derived variables improved the model's explained variances for Nₘₐₛₛ (R²cᵥ 0.31 vs. 0.41, % RSMEcᵥ 3.3 vs. 3.0) and Pₘₐₛₛ (R²cᵥ 0.45 vs. 0.63, % RSMEcᵥ 15.3 vs. 12.5). The predictive performances of Nₘₐₛₛ models using hyperspectral bands only, decreased with increasing structural heterogeneity included in the calibration dataset. To test the independent contribution of canopy structure we additionally fit the models using only LiDAR-derived variables as predictors. Resulting R²cᵥ values ranged from 0.26 for Nₘₐₛₛ to 0.54 for Pₘₐₛₛ indicating considerable covariation between biochemical traits and forest structural properties. Nₘₐₛₛ was negatively related to the spatial heterogeneity of canopy density, whereas Pₘₐₛₛ was negatively related to stand height and to the total cover of tree canopies. In the specific setting of this study, the importance of structural variables can be attributed to the presence of two tree species, featuring structural and biochemical properties different from co-occurring species. Still, existing functional linkages between structure and biochemistry at the leaf and canopy level suggest that canopy structure, used as proxy, can in general support the mapping of leaf biochemistry over broad spatial extents. ispartof: Remote Sensing of Environment vol:211 pages:13-25 status: published