The regeneration of a protected Sonoran Desert cactus since 1800 A.D. over 50,000 km2 of its range

The tall, branched saguaro cactus (Carnegiea gigantea) is perhaps the best-recognized symbol of the desert. However, little is known about the regeneration and future of the species outside of a few well-studied populations. In 2000, data for 537 saguaros were collected in 30 populations throughout the northern Sonoran Desert. A recently developed technique now provides a mechanism by which to reconstruct individual age at multiple populations. This new technique is based on a general growth curve with a site-specific adjustment factor, which I calculate based on local growth data and a recognized relationship with summer rain. Thus, the year of establishment was estimated for all saguaros in each of the populations individually, followed by the merging of all individuals, to create a single regeneration and survivorship curve for the combined regional dataset. Unlike other studies that only look at regeneration at one site, this is the first study to look at the long-term regeneration of the species over an area of more than 50,000 km², nearly the US portion of its range. The results suggest that over the long term, the population is quite stable, with a favorable period of regeneration in the late 1800s and early 1900s. It is also encouraging that the frequency of individuals that established in the most recent time period is relatively high. However, whether these youngest individuals will persist over the long-term in the face of future extreme freezing events (which can substantially thin populations) is not clear.