Long-term Saguaro Monitoring

Saguaro Forest in the Rincon Mountain District, 1935 (top) and 1998 (bottom).

Ray Turner

Saguaro National Park was established in 1933 to protect the famous stand of saguaros at the base of the Rincon Mountains east of Tucson. From the beginning, people were concerned that this stand was dying out. To find out why, all saguaros were measured and counted in a one-square-mile section of the park called Section 17 in 1942. Monitoring of saguaros at the park began in 1942 and, thanks to dedicated researchers, has continued every year since. After more than a half century of poor establishment, survival of young saguaros began to increase in the 1960s. Establishment of new plants surged in the 1980s. The old giants of the Saguaro Forest are slowly being replaced by these slow-growing youngsters.

The photographs at right depict this dramatic transformation. Even though many old, tall saguaros were lost from 1935 to 1998, today we see more young saguaros sprouting up from under nurse trees.

Read more about long-term demographic change in saguaros:

• Saguaro (Carnegiea gigantea) Mortality and Population Regeneration in the Cactus Forest of Saguaro National Park: Seventy-Five Years and Counting
• Demographic Changes Over >70 yr in a Population of Saguaro Cacti (Carnegiea gigantea) in the Northern Sonoran Desert

The Saguaro Census, conducted every 10 years since 1990 in Saguaro National Park, is the primary way the park tracks the population health of its signature plant and associated vegetation community. Results from the 2020 Saguaro Census indicate the park’s saguaro population is healthy. Since 1990, the number of saguaros has nearly doubled, from an estimated 1.15 million to 2 million in 2020.

At the same time, it is clear that the surge of new saguaros entering the population in the late 20th century has now mostly ended. In 2020, only slightly more saguaros were detected than in 2010. Some younger plants were found in foothills and slopes of both districts, where certain soils and rock crevices may retain moisture for longer than in lower, flatter areas. The overall decline in survival of young saguaros can likely be attributed to the extended drought that began in the 1990s and appears to be driven by higher temperatures.

Read more about saguaros and climate:

• The Interaction of Drought and Habitat Explain Space–Time Patterns of Establishment in Saguaro (Carnegiea gigantea)
• The Iconic Saguaro Cactus Across its Landscape
• The Extraordinary Saguaro Bloom of 2021: An Explanation

Research on Saguaro National Park's saguaro population is ongoing—by park staff, the Sonoran Desert Network, university and independent researchers, and through citizen science.

 

• 

  Learn about research in the parks

  Inventory and Monitoring

  The Sonoran Desert Network collects long-term data on the state of key natural resources at Saguaro and 10 other national parks.

• 

  Saguaro Arms Project

  Citizen scientists are helping Saguaro National Park study the growth and symmetry of saguaro arms.

• 

  Saguaro Census

  Every ten years, citizen scientists help Saguaro conduct a census to monitor the long-term health and vitality of saguaros.

 

Notable Saguaro Monitoring Projects

We hope these data are useful for research projects by researchers, college students, and local high school and middle school students.

Notable Saguaro Monitoring Projects

Survey	Description	Documents
Section 17 (1941 and 2011)	In 1941, scientists studied saguaros in a one-mile-square Section 17 to determine if a contagious disease was killing saguaros in the park’s Cactus Forest. Saguaros were mapped, measured and monitored. Seventy years later, in 2011, there was a re-survey of Section 17 to study long-term changes in saguaros.	Dataset Shapefile Report
Historic Plots (1975, 2001, 2010)	Eleven study plots were established in 1941 and 1975 as a long-term study of mortality and recruitment focusing on height and population density. Each saguaro tagged in 1975 was re-located in 2002 and 2010 using GPS units, its status checked (i.e., live or dead), and/or height and number of arms recorded.	Dataset Shapefile Report
Saguaro Census (1990, 2000, 2010)	The census is based on 45 plots of 4 ha each originally established in both districts of the park in 1990 and resurveyed in 2000. This study started with a saguaro count, checking for epidermal browning and measuring saguaro population density and structure. A third resurvey of population density occurred in 2010, without checking for epidermal browning.	Dataset Report
Vegetation Subplots (1990, 2000, 2010)	This project was established in 1990 and resurveyed in 2000 and 2010. The study occurred in small 10x10 meter subplots within the 45 Saguaro Census plots. All perennial species were mapped to provide insights into long-term community dynamics. Vegetation maps were analyzed for differences in species composition, density, and cover through the decades.	Dataset Shapefile Report
Ecotone (2011)	Climate change predictions indicate that the southwestern United States is moving toward an increase of minimum temperature and decreased frequency of freeze events. These predicted changes suggest the geographical and elevational range of the saguaro may change. The ecotone study in 2011 established a baseline for examining these changes more closely.	Dataset Report
Plot Corners and Boundaries	Plot corners and boundaries	Dataset Shapefile

 

Published Research on Saguaro Cacti at Saguaro National Park

Source: Data Store Saved Search 4956. To search for additional information, visit the Data Store.