Radiocarbon analysis confirms the annual nature of sagebrush growth rings

In the Great Basin of North America, big sagebrush (Artemisia tridentata Nutt.) growth rings can be used to reconstruct environmental changes with annual resolution in areas where there is otherwise little such information available. We tested the annual nature of big sagebrush wood layers using accelerator mass spectrometry (AMS) radiocarbon dating. Four cross-sections from 3 sagebrush plants were collected near Ely, Nevada, USA, and analyzed using dendrochronological methods. Ten C-14 measurements were then used to trace the location of the 1963-64 "bomb spike." Although the number of rings on each section did not exceed 60, crossdating was possible within a section and between sections. Years assigned to individual wood layers by means of crossdating aligned with their expected C-14 values, matching the location of the C-14 peak. This result confirmed the annual nature of growth rings formed by big sagebrush, and will facilitate the development of spatially explicit, well-replicated proxy records of environmental change, such as wildfire regimes, in Great Basin valleys.