Effect of climatic variability on δ13C and tree-ring growth in pion 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 pion pine (Pinus edulis) to natural climatic variability using information on physiology and growth as recorded in leaves and tree rings. delta C-13 of annual leaf cohorts (delta C-13(leaf)) and tree rings (delta C-13(ring)) 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 delta C-13 and growth were investigated. delta C-13-climate relationships were stronger for delta C-13(leaf) than for delta C-13(ring) especially at the xeric site. The mean monthly maximum summer temperatures over May through September (summer T (max)) had the strongest influence on delta C-13(leaf). There was a strong negative relationship between RWI with summer T (max) and a strong positive relationship between RWI with October to October precipitation (water-year PPN) at both sites. This suggests that pion pine populations could be vulnerable to decreased growth and, perhaps mortality, in response to warmer, drier conditions predicted by models of global climate change.