History of the “Section 17” Saguaro Survey in Saguaro National Park

Swann, Don

In 1941, scientists studied saguaros in a one-mile-square section, named Section 17, of Saguaro National Park’s Rincon Mountain District as part of an experiment to determine if a contagious disease was killing saguaros in the park’s “Cactus Forest” area. Long-term monitoring has continued in Section 17 since 1941. Many of the records from the 1941 study have survived, including the original maps, reports, and data. In 2011, Saguaro National Park worked with school groups and citizen scientists to study long-term changes in saguaros by repeating the survey of Section 17, seventy years after the original survey in 1941. This Appendix describes the history of Section 17, which includes study hypothesis, design and execution in 1941. To experimentally determine whether removing the diseased saguaros would increase the survivorship of those that showed no signs of the disease, Section 17 was divided into treatment control areas. Results of the original survey did not support bacterial necrosis as cause of the saguaro decline. The black fluid they were oozing as they died appears to have been, in many cases, a secondary effect of tissue damaged by freezing, not disease. Due to negative results of the Section 17 experiment, attention turned to other potential causes of the decline of saguaros in Saguaro National Park. In the 1960s and 1970s the focus turned increasingly to ecological factors such as the relationship between saguaros and nurse trees, the role of rodent herbivory, and the importance of climate, particularly freezing weather and drought. Plots of saguaros, including Section 17, have continued to be monitored via a Saguaro Census in ten-year intervals.

History of the “Section 17” Saguaro Survey in Saguaro National Park

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