Variation in age and height of onset of reproduction in the saguaro cactus (Carnegiea gigantea) in the Sonoran Desert

摘要

The objective of this study is to determine the height and age at which reproduction begins (i.e., production of flowers and fruits; the transition to adulthood) in the giant saguaro cactus (Carnegiea gigantea) in four geographically and environmentally distinct populations, and to relate observed variability to environmental differences. The onset of reproduction has been estimated at a height of 2.2 m in near optimal conditions. This value has been widely accepted and applied to populations in less optimal conditions, although variations under less ideal conditions have not been investigated. In addition, previous research has demonstrated that Carnegiea growth rates are highly variable over their range. Thus, even if 2.2 m is a consistent transition height to adulthood over their range, the age of individuals in different populations would be different. I investigate the age and height at which this transition occurs.