Trade-offs in Functional Investments Influence Tree Mortality During 2012-2016 California Drought

California experienced a severe to exceptional drought from 2012 -2016, with combined dryness and high temperatures making its severity unprecedented. The drought played a role in the death of more than 150 million trees across California, with causes of mortality linked to tree height, soil moisture, groundwater depletion, and insect outbreaks. We used published tree mortality data (2009-2016) for the US National Ecological Observatory Network (NEON) Soaproot Saddle and Lower Teakettle sites in the Sierra Nevada Mountains in conjunction with annual foliar trait maps derived from NASA's AVIRIS-Classic imaging spectrometer to test linkages between pre-mortality plant functional traits and drought-related dieback. Trait maps were generated for images acquired over the study area in June each year during the core of the drought (2013-2016), and were linked to mortality data from 2014 and 2016 to test whether trait syndromes (combinations of trait values) were more or less associated with mortality as the drought progressed. Results show a functional trade-off between nonstructural carbohydrates (NSC, comprised of sugars and starches, which are usually associated with maintenance of osmoregulation under drought conditions) and defense compounds (phenolics) throughout the drought for all trees, regardless of eventual fate. While trees followed similar adaptive trends across years, within-year trends show that trees that survived the drought had higher concentrations of nitrogen (associated with photosynthetic capacity) and nonstructural carbohydrates and decreased levels of lignin, phenolics, and cellulose compared to trees that died. This suggests that during drought trees that invest in maintenance and photosynthetic capacity exhibit an advantage over those that allocate resources toward leaf structure and defense (cellulose, lignin, phenolics).