Early Recognition of Changes in the Health Status of Norway Spruce with Hyperspectral Data

Abstract

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.