Tree-Ring Variation in Pinyon Predicts Likelihood of Death Following Severe Drought

A severe drought in northern Arizona caused widespread pinyon (Pinus edulis) mortality, exceeding 40% in some populations. We measured tree-ring widths of pinyons that survived and that died in three sites designated as “high,” “medium,” and “low” stress. Growth characteristics during the previous 10–15 years can be used to predict the likelihood of drought-induced death; dead trees exhibited 1.5 times greater variation in growth than live trees. A model of ring-width deviations vs. drought severity showed a loss of “climatic sensitivity” with age in dead trees. These differences were independent of site. We found two distinct tree types that are predisposed to die during drought; highly sensitive young trees, and insensitive older trees. As the Southwest has a dynamic climate typified by severe droughts, it is important to understand how droughts act as bottleneck events to affect a dominant tree in a major vegetation type of the United States.