Goals of the first project (2007-2011):
The long-lived (125-175 yrs) saguaro cactus (Carnegiea gigantea) is a defining floristic element of the Sonoran Desert, occurring throughout southern Arizona and western Sonora, Mexico. Saguaro and other columnar cacti (cardón, Pachycereus pringlei; organ pipe cactus, Stenocereus thurberi) are “foundation species” in the Sonoran Desert because significant amounts of water, nutrients and energy are provided to consumers from fruits, seeds and stems of these large succulents. This project will examine the interaction of climate and the saguaro in order to quantify the impact of climate variability (both past and future) on the ecophysiology of saguaro and the saguaro-based ecosystem of the Sonoran Desert. This will be done by constructing precisely dated, high resolution records of oxygen, hydrogen, and carbon isotope ratios in spines grown and retained throughout the life of saguaro cacti across a gradient in water stress and seasonality of precipitation. Oxygen and hydrogen isotope ratios of spines reflect the supply of water and variation in relative humidity. Carbon isotope ratios reflect photosynthetic efficiency and water stress. Comparison of these annually-resolved stable isotope records with growth rates, fecundity, and instrumental records of climate anomalies covering the last 50 – 80 years will reveal the cactus’ physiological response to local environmental variation.
Kevin Hultine, Research Ecologist, The Desert Botanical Garden, Phoenix.
David Williams, Professor, Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY.
Nathan English, Research Fellow, School of Earth and Environmental Sciences, James Cook University, Australia.
Future work expands this approach to columnar cactus in general. Adding more than 30 species with a range of plant geometries and adaptations to this work.