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Tree-ring carbon isotope data and drought maps
for the U.S. Southwest

Southwest USA map showing 14 Pinyon Pine sites
Fig. 1. 14 pinyon pine sites used to develop Drought Indices using d13C analysis. The Ozena, Hawthorne and Lamoille sites had Pinus monophylla and the other had Pinus edulis.

The Sites and Collections
Tree-ring samples from a set of 14 pinyon pine sites (Pinus edulis and Pinus monophylla) were collected across 6 states in the American Southwest (Fig. 1) between 1983 and 1986 (described in Leavitt and Long 1985, 1986, 1988, 1989b). Elevations of the sites (Table 1) range from about 1400 to 2500 m (ca. 4500 to 8200 ft). Normally, four orthogonal (approximately cardinal compass directions) cores were taken from 6-10 trees, and the rings of the 4 cores from 4 of the trees (selected for fewest missing rings, age, etc.) were used in the isotopic analysis. Rings were dated and separated into pentads (e.g., 1900-04, 1905-09, etc.), and the pentads from the four cores from four trees were pooled into composite samples for each site. Holocellulose was separated from the pentads, combusted to CO2 and analyzed for stable-carbon isotope composition (d13C (w.r.t. PDB) = [{13C/12Csample} / {13C/12Cstandard} - 1] x 1000) on a mass-spectrometer.

Table 1. Approximate site elevations and the beginning year contributing to the isotope drought maps.

SITE Elevation (m) Beginning Year Final Year
Kane Springs, UT 1965 1600 2001
Alton, UT 2245 1600 1999
Dry Canyon, CO 2150 1625 2000
Lower Colonias, NM 2375 1655 2001
Aztec, NM 2080 1710 2001
Cerro Colorado, NM 2500 1650 2001
Ozena, CA 1370 1750 2000
Hawthorne, NV 2330 1620 2001
Mimbres, NM 2025 1790 2001
Owl Canyon, CO 1860 1600 2001
NC AZ, AZ 1470 1725 2001
NE AZ, AZ 2090 1700 2000
Gate Canyon, UT 2220 1600 1999
Lamoille, NV 2130 1685 2000
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