Past climate changes and ecophysiological responses recorded in the isotope ratios of saguaro cactus spines English, Nathan B. ; Dettman, David L. ; Sandquist, Darren R. ; Williams, David G. Abstract Publication: Oecologia Pub Date: November 2007 DOI: 10.1007/s00442-007-0832-x Bibcode: 2007Oecol.154..247E