Characterizing Eucalypt Leaf Phenology and Stress with Spectral Analysis

Detection of stress with remote sensing in any vegetation type relies on development of methods that highlight properties associated with stress which are discernable from background variation, such as phenological changes. Therefore the nature (and timing) of phenological foliar change needs to be systematically compared to foliar stress symptoms with physical, biochemical and optical analyses. Two such case studies with eucalypt species are presented here, including Eucalyptus globulus and Eucalyptus pilularis. Studies with both eucalypt species have shown that different leaf ages can be associated with alterations in pigments and properties that are as pronounced as those occurring for well-developed stress responses (potassium deficiency for E. globulus and low nutrient and cold exposure in E. pilularis). Chlorophyll, carotenoid and anthocyanin content were analysed, as well as specific leaf area and water content. Significant differences between leaf ages were detected for many of these leaf pigments and properties, but the significant differences between healthy and stressed leaves were usually of greater magnitude. Only carotenoid content was not significantly different with leaf age for E. globulus, but was significantly different with potassium-deficiency. This is a basis to further investigate the potential of carotenoids to discern stressed leaves from phenological changes. Preliminary data shown here provides a background for ongoing spectral research on this theme for eucalyptus.