Detection of stress in coniferous forest trees with the VIRAF spectrometer

The Visible Infrared Reflectance Absorbance Fluorescence (VIRAF) spectrometer was applied in outdoor measurements to compare the needles of two spruce trees differently affected by the forest decline in the Northern Black Forest in Germany. Changes of the reflectance signatures due to loss of chlorophyll or other damage effects are interpreted with the help of other techniques currently used for the evaluation of physiological activity. The VIRAF spectrometer was used to examine the spectra of reflectance, absorption, and chlorophyll fluorescence. The measurements were carried out with the same sample without changing its position. By means of the two-wavelength chlorophyll fluorometer and pulse amplitude modulation fluorometer the fluorescence induction kinetics and several fluorescence parameters were determined as an indicator of vitality. In addition, the rate of photosynthetic CO₂ fixation and the stomatal closure were studied using a CO₂ H₂O porometer