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On the Age and Growth Rate of Giant Cacti: Radiocarbon Dating of the Spines of Cardon (Pachycereus Pringlei)

Published online by Cambridge University Press:  30 March 2016

Mariana Delgado-Fernández*
Affiliation:
Centro de Investigaciones Biológicas del Noroeste, Instituto Politécnico Nacional 195, La Paz, Baja California Sur 23096, México
Pedro P Garcillán
Affiliation:
Centro de Investigaciones Biológicas del Noroeste, Instituto Politécnico Nacional 195, La Paz, Baja California Sur 23096, México
Exequiel Ezcurra
Affiliation:
University of California-Riverside, 900 University Avenue, Riverside, California 92521, USA
*
*Corresponding author. Email: mdelgado@pg.cibnor.mx.

Abstract

Age estimation has been a limiting factor in the study of giant columnar cacti. In order to test the feasibility of using radiocarbon methods to estimate the age of the giant cardon cacti (Pachycereus pringlei), we selected six sites spanning the latitudinal and precipitation range of the species in the Baja California peninsula. In each site, we selected four individuals of different heights and sampled a spine from the lowest areole in the stem. The age of the spine was estimated using 14C dating, and the mean annual growth rate of the plant was calculated dividing the height of the lead shoot by the plant’s age. Mean annual growth rate was 0.098 m/yr, with values varying between 0.03 and 0.23 m/yr. Within the range of plants sampled, mean annual growth rates were significantly correlated with the height of the plant (r 2=0.82, P<0.0001), and no other site-specific variable such as precipitation or latitude was a significant predictor of mean annual growth rates. A model integrating mean growth rate versus height showed that relatively small differences in growth rates between plants accumulate during the plants’ lifetime, so that plants of similar size may have very different ages. We conclude that 14C dating provides a robust method to explore the growth and demography of columnar cacti.

Information

Type
Research Article
Copyright
© 2016 by the Arizona Board of Regents on behalf of the University of Arizona 

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