About Section 17

 

Our Changing Cactus Forest

Shortly after the establishment of Saguaro National Monument in 1933, the saguaro population began declining. Park rangers feared that over time, there would be no saguaros left, thus beginning a study to determine why these newly protected cacti were dying. 

Scientists conducted censuses of the majestic saguaro in an effort to understand why the population was declining.  In 1941, Paul Lightle, Lake Gill and James Mielke counted all 13,304 cacti in Saguaro National Park East, Section 17.  Section 17 is indicated on the map below.


At the time, the decline in saguaros was thought to have been caused by a contagious bacterial disease. To experimentally test this hypothesis, dead and dying saguaros were removed and buried and smaller lesions caused by bacterial rot were treated with antibiotics in the southern half of the section, while saguaros in the northern half of the section were simply monitored. 


After monitoring the plots for 9 years, Gill determined that there was no evidence to support a contagious bacterial disease and that the continued lack of saguaro reproduction in the cactus forest was a major problem.
Sub plots within section 17 have been monitored continuously since 1941, making section 17 one of the longest vegetation monitoring programs in the National Park Service.


In the 1950s research turned towards a disease called bacterial necrosis, though to be spread by a moth.



By the 1960-70s research turned towards ecological factors that could be both killing older large saguaros, and preventing new saguaros from growing.

 Scientists now believe that many saguaros died from two intense freezes in 1937 and 1939 rather than bacterial rot.  Factors contributing to the lack of small saguaros were probably wood-cutting which removed the saguaros’ protective “nurse trees” and cattle grazing.


Starting in 2011, we are re surveying the entire section 17 for the first time since the early 1940s. Because saguaros are such slow growing plants, long term monitoring projects are one of the only ways we can study their ecology and life cycle. In this citizen science based study, volunteers will be counting, measuring and recording important information about their habitat. If you'd like to be involved in the current Section 17 Saguaro Census, please visit the Volunteer Info page.