Estimating light use efficiency and leaf area index in youg eucalypts with hyperspectral reflectance

Monitoring of growth and health is vital for optimal management of forests, but represents a high cost. Remote sensing offers a range of options for capturing timely and spatially explicit data related to growth and health, including estimation of leaf area index (LAI) and light use efficiency (LUE), the key determinants of primary productivity. Studies of pot-grown Eucalyptus globulus have shown that pre-dawn chlorophyll fluorescence, xanthophyll pigment status and the photochemical reflectance index (PRI) are well correlated at the leaf-level across a range of stress symptoms. In addition, leaf-level relationships between the PRI and LUE were good in young field- grown E. globulus at an experimental site in southern Tasmania, Australia. At this low-rainfall site, treatments were applied including low and adequate nitrogen applications to irrigated or non-irrigated plots. Half the plants in each plot were also artificially defoliated. Crown-level studies revealed that LAI of young trees before and after defoliation was most strongly correlated with NDVI (R² 0.65). LAI was also significantly related to a number of other spectral vegetation indices, including the red edge position and MCARI2. After 6 months of nutrient and irrigation treatments crown studies were to investigate detection of physiological differences between trees with spectral reflectance. Determinations of pre-dawn chlorophyll fluorescence and LUE suggested that trees were all of relatively healthy status and differences between treatments subtle. The PRI values were consistent with the healthy status of the trees and did not vary between treatments. While correlations between the PRI and other physiological variables were poor at the crown-scale, results here warrant further investigation.