Predicting tropical tree mortality with leaf spectroscopy

• DOI: 10.1111/btp.12901
• Publication Date: 2020-12-22T19:06:00Z
• Authors: Christopher E. Do...; Alexander W. Chee...; Terhi Riutta; Eleanor R. Thomson; Alexander Shenkin; Andrew T. Nottingham; Elizabeth M. Telford; Walter Huaraca Hu...; Noreen Majalap; Yit Arn Teh; Patrick Meir; Yadvinder Malhi
• Keywords: 580; Other Ecology and Evolutionary Biology; 0301 basic medicine; bepress|Life Sciences|Forest Sciences|Forest Biology; 0303 health sciences; bepress|Life Sciences|Plant Sciences|Other Plant Sciences; bepress|Life Sciences|Forest Sciences; Ecology and Evolutionary Biology; Plant Sciences; Life Sciences; bepress|Life Sciences|Ecology and Evolutionary Biology|Other Ecology and Evolutionary Biology; 15. Life on land; bepress|Life Sciences|Ecology and Evolutionary Biology; 03 medical and health sciences; bepress|Life Sciences; 13. Climate action; Other Plant Sciences; bepress|Life Sciences|Plant Sciences; Forest Biology; Forest Sciences

AbstractDo tropical trees close to death have a distinct change to their leaf spectral signature? Tree mortality rates have been increasing in tropical forests, reducing the global carbon sink. Upcoming hyperspectral satellites could be used to predict regions close to experiencing extensive tree mortality during periods of stress, such as drought. Here we show, for a tropical rainforest in Borneo, how imminent tropical tree mortality impacts leaf physiological traits and reflectance. We measured leaf reflectance (400–2500 nm), light‐saturated photosynthesis (Asat), leaf dark respiration (Rdark), leaf mass area (LMA), and % leaf water across five campaigns in a six‐month period during which there were two causes of tree mortality: a major natural drought and a co‐incident tree stem girdling treatment. We find that prior to mortality, there were significant (p < 0.05) leaf spectral changes in the red (650–700 nm), the NIR (1,000–1,400 nm), and SWIR bands (2,000–2,400 nm) and significant reductions in the potential carbon balance of the leaves (increased Rdark and reduced Asat). We show that the partial least squares regression technique can predict mortality in tropical trees across different species and functional groups with medium precision but low accuracy (r2 of .65 and RMSE/mean of 0.58). However, most tree death in our study was due to girdling, which is not a natural form of death. More research is needed to determine if this spectroscopy technique can be applied to tropical forests in general.