The 2012-2015 California drought induced a pulse of tree mortality throughout the state that was widespread and severe. In 2016, the state rain and snowfall levels returned closer to normal, but in 2017 conditions appear to have reverted back in the direction of drought. This occurrence provides an opportunity to explore the persistence of drought effects on forest ecosystems. We use a time series of canopy water content, derived from laser guided imaging spectroscopy data, to quantify tree stress in response to the drought throughout the entire state, an approach we have previously demonstrated to be effective at anticipating drought-induced tree mortality. We then couple this indicator of physiological response to drought with climatological indicators, used to quantify 2016 levels of renewed precipitation. We use these datasets to answer two questions: 1) How do areas that have been subject to significant drought conditions over a series of years react to renewed, short-term (annual) precipitation, and 2) how do forests respond if drought conditions recur after a temporary reprieve?
Results/Conclusions
Our findings indicate that despite the temporary relief in 2016, significant physiological indicators of water stress were observed in many areas throughout the state, often coinciding with areas of renewed precipitation. This continued response is likely due to a combination of drought-related weaknesses and bark-beetle outbreaks. Similar to the relationships between water stress and tree mortality that we have demonstrated previously, the response to renewed precipitation is specific to particular ecosystems. While data for the current season are still arriving, preliminary results indicate that areas with renewed climatological drought behave approximately the same physiologically as if no reprieve occurred at all.