Comparison of Tree Species Sensitivity to High- and Low-Extreme Hydroclimatic Events

Abstract

We present here a six-species comparison of tree-ring growth response to extremes (below the 30th and above the 70th percentile) in temperature, precipitation, and corresponding streamflow. The species compared are Pinus edulis (PIED), Pseudotsuga menziesii (PSME), Pinus ponderosa (PIPO), Pinus flexilis (PIFL), Pinus aristata (PIAR), and Picea engelmannii (PCEN). Sensitivity was determined using contingency scores obtained by comparing tree-ring growth at different lags with hydroclimatic observations from the Upper Colorado River Basin in the southwestern United States. The scores were computed using dual scaling methods in which the higher scores are assigned to stronger relationships between tree-ring growth and severe hydroclimatic occurrences. At lag 0, PIED and PSME present the greatest sensitivity to severe streamflow events. For precipitation and temperature the most sensitive species at lag 0 are PIED and PIPO. PIAR and PCEN show no significant relationship with extreme hydroclimatic events. PIFL shows more uniform lag-to-lag scores, suggesting a higher year-to-year persistence for this species. In general, tree-ring growth for all sensitive species is more responsive to hot-dry than to cool-moist extreme conditions. The scoring method proposed in this study for the analysis of tree-ring records proved to be a useful tool for evaluating ring-width sensitivity to extreme climatic forcing.