Dying light: Detecting tree mortality risk with chlorophyll fluorescence

Abstract

Increased greenhouse emissions have altered Earth's climate, resulting in rapid climate change which has brought warm droughts-especially in semi-arid regions-leading to forest die-off and dieback. Physiological stresses associated with climate change pose a great risk to tree survival, as future climate changes are likely to increase the intensity of drought. Some of these effects can be observed in species such as pinon pine (Pinus edulis), which typically have a high drought tolerance but have succumbed to widespread drought-induced mortality in recent decades, likely due to hydraulic failure. Currently, remotely sensing hydraulic failure is not possible. However, our results suggest chlorophyll fluorescence in dark-adapted samples is an indicator of water stress and the variation of chlorophyll fluorescence within a tree increases as drought stress prolongs. With continued observation, we believe chlorophyll fluorescence will show to be a useful proxy for hydraulic failure to aid mortality predictions as well as predict how future climate changes will impact terrestrial vegetation and climate feedback loops.