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.