Comparing response of Pinus edulis tree-ring growth to five alternate moisture indices using historic meteorological data

Annual growth of semiarid tree species is generally limited by a period of water deficit and this relationship can be reflected in interannual variation in tree-ring width of semiarid species such as Pinus edulis, a piñon pine that is widely distributed across the southwestern United States. Tree-ring width of P. edulis and other semiarid tree species is most frequently related to annual precipitation amount alone or to the Palmer drought severity index (PDSI). But water deficit and associated variation in moisture can also be described using numerous other indices such as the standardized precipitation index (SPI), and a comparison of the performance of several indices that relate historical climate data to tree-ring variation in P. edulis is lacking. We compared abilities to predict radial tree-ring growth of P. edulis using five metrics of water availability: PDSI, two indices based on precipitation alone (total precipitation and SPI), and two indices that factor in temperature to determine water deficit (based on Walter climate diagrams that use monthly precipitation and temperature). Each metric was evaluated over three commonly used time periods (water year, calendar year, and June-August) using the limited available data from P. edulis sites in the southwestern USA where co-located tree-ring and weather data were available. Our results indicate that PDSI was the best predictor of P. edulis ring widths, regardless of time period, and provide a first comparative test of PDSI with SPI and Walter indices that can be further tested as larger data sets become available.