Statistical comparison of spectral and biochemical measurements on an example of Norway spruce stands in the Ore Mountains, Czech Republic

The physiological status of vegetation and changes thereto can be monitored by means of biochemical analysis of collected samples as well as by means of spectroscopic measurements either on the leaf level, using field (or laboratory) spectroradiometers or on the canopy level, applying hyperspectral airborne or spaceborne image data. The presented study focuses on the statistical comparison and ascertainment of relations between three datasets collected from selected Norway spruce forest stands in the Ore Mountains, Czechia. The data sets comprise i) photosynthetic pigments (chlorophylls, carotenoids) and water content of 495 samples collected from 55 trees from three different vertical levels and the first three needle age classes, ii) the spectral reflectance of the same samples measured with an ASD Field Spec 4 Wide-Res spectroradiometer equipped with a plant contact probe, iii) an airborne hyperspecral image acquired with an Apex sensor. The datasets cover two localities in the Ore Mountains that were affected differently by acid deposits in the 1970s and 1980s. A one-way analysis of variance (ANOVA), Tukey’s honest significance test, hot spot analysis and linear regression were applied either on the original measurements (the content of leaf compounds and reflectance spectra) or derived values, i.e., selected spectral indices. The results revealed a generally low correlation between the photosynthetic pigments, water content and spectral measurement. The results of the ANOVA showed significant differences between sites (model areas) only in the case of the leaf compound dataset. Differences between the stands on various levels of significance exist in all three datasets and are explained in detail. The study also proved that the vertical gradient of the biochemical and biophysical parameters in the canopy play a role when the optical properties of the forest stands are modelled.