A new drought tipping point for conifer mortality

(Huang et al 2015 Environ. Res. Lett. 10 024011) present a method for predicting mortality of ponderosa pine (Pinus ponderosa) and pinyon pine (Pinus edulis) in the Southwestern US during severe drought based on the relationship between the standardized precipitation–evapotranspiration index (SPEI) and annual tree ring growth. Ring growth was zero when SPEI for September to July was −1.64. The threshold SPEI of −1.64 was successful in distinguishing areas with high tree mortality during recent severe drought from areas with low mortality, and is proposed to be a tipping point of drought severity leading to tree mortality. Below, I discuss this work in more detail