Evaluating the Seasonality of Remote Sensing Indicators of System State for Eucalyptus Grandis Growing on Different Site Qualities

The stability of remote sensing indicators of leaf water, chlorophyll and nutrients to discriminate between Eucalyptus grandis growing on different site qualities in KwaZulu-Natal, South Africa was evaluated for two growing seasons (winter and early summer). Site quality was defined by the total available soil water (TAW). Canopy reflectance spectra for 68 trees (winter) and 45 trees (summer) from good, medium, and poor sites were collected on clear sky days using an ASD spectroradiometer. Two-way analysis of variance showed that the discriminatory capabilities of leaf water, chlorophyll, and nutrient concentrations for E. grandis growing on different site qualities, are seasonal by nature. Leaf water and chlorophyll indices were better indicators of site quality in winter than foliar nutrient concentrations of N, P, and K, which in turn performed better in summer. These results will help to define the sensing timeframe for monitoring E. grandis growth in KwaZulu-Natal.