Crown‐scale evaluation of spectral indices for defoliated and discoloured eucalypts

Abstract

Remote sensing for evaluation of canopy health in plantation eucalypts is a realistic option for forest managers in the near future if reliable and robust methods of spectral analysis can be developed. Pot‐grown eucalypts of three species important to the Australian plantation industry were used for crown‐scale spectral (400–1000 nm) evaluations of vegetation indices as indicators of common symptoms of stress. When defoliation treatments (in E. globulus) or exposure to cold and nutrient deprivation (in E. pilularis) resulted in large differences in leaf cover, the red edge position and slope indices, two normalized difference vegetation indices (NDVIs), modified chlorophyll absorption ratio index 2 (MCARI2) or modified triangular vegetation index 2 (MTVI2) were most strongly correlated to leaf cover. However the NDVIs were significantly affected by soil background in a study with E. globulus. The percentage of red leaves resulting from stress treatment was most strongly correlated with the anthocyanin reflectance index (ARI) and red‐green index (RGI) in both E. grandis and E. pilularis, however the RGI was affected by background type in the E. globulus study while the ARI was not. Exposure to cold and nutrient deprivation led to marked changes in leaf cover for E. pilularis but not in E. grandis and a much more reduced level of chlorophyll in E. pilularis than is suspected in E. grandis. In E. globulus, defoliation from the upper crown was easier to detect with spectral data than from the lower crown. Results were generally comparable to studies of eucalypt crown condition from native forests.

Acknowledgements

This research was funded by an Australian Research Council Linkage grant (LP0453591) and Forestry Tasmania, Forests and Industries Council of Tasmania, Forests NSW, Gunns Ltd. and WAPRES. We thank Stephen Ridge for assistance while involved in a Summer Studentship supported by the Tasmanian Institute of Agricultural Research. Mr. Malcolm Hall (CSIRO Forestry) assisted with maintenance of glasshouse material and the stress study. Dr. Neil Sims and Dr. Darius Culvenor (Ensis Remote Sensing Research Group) contributed useful discussion for developing the crown‐scale system. Dr. Sims, Dr. Glenn Newnham and Ass. Prof. Mary Martin provided helpful comments which improved earlier versions of this paper.