Possible climatic response of delta ¹³C in leaf cellulose of pinyon pine in Arizona, U.S.A.

Leaves of pinyon pine (Pinus edulis) were collected from 10 living trees at 9 sites in Arizona and New Mexico, representing elevations from 1200 to 2200 m. Stable-carbon isotopic analysis was performed on cellulose isolated from the whole-leaf material. In spite of the range of conditions, the delta ¹³C response varies only over approx 1per mille, with an average variance among leaves of the same tree of 0.4per mille. These values were regressed with elevation and with monthly, seasonal and annual climatic data from nearby climatological stations. Linear relations of delta with T and precipitation yield mostly positive correlations, not significant at 95%. Because of high delta ¹³C values for the the highest elevation sites, the regressions improve greatly for second-order polynomials of elevation and T. The mechanism for higher delta ¹³C at higher elevations is not clear, but may be related to length of growing season. There may be some potential for reconstructions based on strong linear relations derived from the lower elevation trees.-P.Br.