N.G. McDowell Craig D. Allen C. Mora N.B. English 2011 <p>Tree-ring carbon and oxygen isotope ratios from live and recently dead trees may reveal important mechanisms of tree mortality. However, wood decay in dead trees may alter the δ¹³C and δ¹⁸O values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and α-cellulose from live and dead specimens of ponderosa pine (<i>Pinus ponderosa</i>), one-seed juniper (<i>Juniperous monosperma</i>), piñon pine (<i>Pinus edulis</i>) and white fir (<i>Abies concolor</i>), including those with fungal growth and beetle frass in the wood, to determine if α-cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the δ¹³C or δ¹⁸O values of α-cellulose and whole wood was the same for both live and dead trees across a large range of inter-annual and regional climate differences. The method of α-cellulose extraction, whether Leavitt-Danzer or Standard Brendel modified for small samples, imparts significant differences in the δ¹³C (up to 0.4‰) and δ¹⁸O (up to 1.2‰) of α-cellulose, as reported by other studies. There was no effect of beetle frass or blue-stain fungus (<i>Ophiostoma</i>) on the δ¹³C and δ¹⁸O of whole wood or α-cellulose. The relationships between whole wood and α-cellulose δ¹³C for ponderosa, piñon and juniper yielded slopes of ~1, while the relationship between δ¹⁸O of whole wood and α-cellulose was less clear. We conclude that there are few analytical or sampling obstacles to retrospective studies of isotopic patterns of tree mortality in forests of the western United States.</p> application/pdf 10.1002/rcm.5192 en Wiley The effects of α-cellulose extraction and blue-stain fungus on retrospective studies of carbon and oxygen isotope variation in live and dead trees† article