Oxygen isotope ratios from tree rings containing compression wood

Abstract Oxygen isotope determinations on the α-cellulose of tree rings cut from two leaning Picea engelmannii revealed significant differences between results from normal and compression wood radii. Nine samples (10-year periods) from the normal wood radius (1721–1953) in one tree showed good agreement with proxy climate information and maximum differences of 1.8‰ between the “warmest” and “coolest” decades sampled. Differences of equivalent magnitude were found between samples from the same decade from normal and compression wood radii. These differences are strongly related to the amount and/or density of compression wood present and suggest that sampling for paleoclimatic work should be restricted to complacent, erect trees without compression wood rings.