Saguaro Census 2010 Final Report

O'Brien, Kara; Swann, Don; Springer, Adam

We studied the demographics of the saguaro cactus (Carnegiea gigantea), Saguaro National Park‟s signature species, at the park during the 2010 Saguaro Census. The Census is based on 45 plots of 4 ha each that were originally established in both districts of the park in 1989-1990 by Duriscoe and Graban (1991, 1992), and re-surveyed in 2000 by Turner and Funicelli (2000). Compared to 1990 and 2000, we observed many more saguaros on Census plots, particularly young saguaros (<1 m in height). In the Rincon Mountain District, the number of saguaros observed has increased 60.0% since 1990 and 40.7% since 2000. In the Tucson Mountain District, the number has increased 67.4% since 1990 and 10.3% since 2000. Using the same method as Turner and Funicelli (2000), we estimated that there are approximately 1,896,030 saguaros in Saguaro National Park. In 2000, they estimated that there were 1,624,821 saguaros in the park, and had been 1,145,784 in 1990. Based on height-age models, we estimated when young saguaros have entered the population. Our results indicate that saguaro recruitment was high during the 1970s through the early 1990s throughout the park, but has declined during the past 10-15 years. Nevertheless, the saguaro population in both districts of Saguaro National Park now has a large number of young saguaros. Given the current trends, we expect that the landscape view of the park, particularly in the Rincon Mountain District‟s “Cactus Forest” area near the Visitor Center and Loop Road, will once again begin to resemble the view seen by visitors when the park was first created in the 1930s. The 2010 Saguaro Census was the first in which volunteer “Citizen Scientists” conducted nearly all of the field work under the direction of student employees and interns, and this aspect of the Census was a great success. It is hoped that the Census will continue as a long-term monitoring effort at Saguaro National Park, with plots surveyed every 10 years into the future.