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.
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