Effect of climatic variability on δ13C and tree-ring growth in piñon pine (Pinus edulis)

Understanding the response of long-lived species to natural climatic variability at multiple scales is a prerequisite for forecasting ecosystem responses to global climate change. This study investigated the response of piñon pine (Pinus edulis) to natural climatic variability using information on physiology and growth as recorded in leaves and tree rings. δ13C of annual leaf cohorts (δ13Cleaf) and tree rings (δ13Cring) were measured at an ecotonal/xeric site and a mid-range/mesic site. Ring width indices (RWI) were used to estimate annual growth of individual trees. Relationships between seasonal and annual climate parameters and δ13C and growth were investigated. δ13C–climate relationships were stronger for δ13Cleaf than for δ13Cring especially at the xeric site. The mean monthly maximum summer temperatures over May through September (summer Tmax) had the strongest influence on δ13Cleaf. There was a strong negative relationship between RWI with summer Tmax and a strong positive relationship between RWI with October to October precipitation (water–year PPN) at both sites. This suggests that piñon pine populations could be vulnerable to decreased growth and, perhaps mortality, in response to warmer, drier conditions predicted by models of global climate change.