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The focus of this analysis is on the early detection of forest health changes, specifically that of Norway spruce (Picea abies L. Karst.). In this analysis, we planned to examine the time (degree of early detection), spectral wavelengths and appropriate method for detecting vitality changes. To accomplish this, a ring-barking experiment with seven subsequent laboratory needle measurements was carried out in 2013 and 2014 in an area in southeastern Germany near Altötting. The experiment was also accompanied by visual crown condition assessment. In total, 140 spruce trees in groups of five were ring-barked with the same number of control trees in groups of five that were selected as reference trees in order to compare their development. The laboratory measurements were analysed regarding the separability of ring-barked and control samples using spectral reflectance, vegetation indices and derivative analysis. Subsequently, a random forest classifier for determining important spectral wavelength regions was applied. Results from the methods are consistent and showed a high importance of the visible (VIS) spectral region, very low importance of the near-infrared (NIR) and minor importance of the shortwave infrared (SWIR) spectral region. Using spectral reflectance data as well as indices, the earliest separation time was found to be 292 days after ring-barking. The derivative analysis showed that a significant separation was observed 152 days after ring-barking for six spectral features spread through VIS and SWIR. A significant separation was detected using a random forest classifier 292 days after ring-barking with 58% separability. The visual crown condition assessment was analysed regarding obvious changes of vitality and the first indication was observed 302 days after ring-barking as bark beetle infestation and yellowing of foliage in the ring-barked trees only. This experiment shows that an early detection, compared with visual crown assessment, is possible using the proposed methods for this specific data set. This study will contribute to ongoing research for early detection of vitality changes that will support foresters and decision makers.

Recent studies show that Norway spruce monocultures are fragile with regard to climate changes (LWF) and furthermore vulnerable to different threats like storm damages or insect infestations. Especially due to the last mentioned, early detection of changes in the health status could help minimizing economical loss. The fundamental idea which lead to Norway spruce needle re flectance spectra analysis is, that within a time period of five months after artificial weakening of trees, reflectance spectra of needles show differences, which might make it possible to distinguish between weakened and control trees. Artificial weakening through ring-barking leads to a wide time frame for change detection due to a slow die back of trees. The point of time where needles still appear green but changes in reflectance spectra indicate a decline in the health status of ring-barked trees is of special interest. During the whole period needles were sampled directly within tree crowns and reflectance spectra were measured in a spectral laboratory. Comparison of spectra between both groups was conducted with the principal component analysis, the Jeffries-Matusita Distance and different health related indices. The results show that it is not possible to distinguish between ring- barked and control trees with the applied methods after a period of five months. This thesis illustrates that trees are complex systems with regard to their water -and assimilate transportation system. Time span from ‘damage’ to ‘symptom’ is dependent on various different factors. This makes ‘early’ recognition of health problems with needle reflectance spectra difficult in forest stands.