The Saguaro Census is large “citizen science” project that helps Saguaro National Park keep track of the population and health of its namesake plant. The Census started in 1990, takes place every 10 years, and is completed with the help of hundreds of volunteers who help to measure, map and collect data on thousands of saguaros.

The 2020 Saguaro Census began in October, 2019 and ended in April, 2020- just before the pandemic hit. 518 volunteers participated in the Census along with park staff and NextGen rangers. Data was collected from 21,517 individual saguaros located at 45 random plots. Based on that statistical data, it’s estimated that the saguaro population at Saguaro National Park is 2,066,281 with 460,478 at the Rincon Mountain District and 1,605,803 at the Tucson Mountain District. This is an increase of over 100,000 from the 2010 Saguaro Census results.

Interpreting the Saguaro Census results is complicated because the saguaro population changes slowly. Saguaros are slow-growing plants that can live more than 150 years but, conditions need to be perfect for new saguaros to germinate. The real value of the 10-year Census is the insight it provides about long-term changes over many decades. The major findings from the 2020 Census are; 1) The park’s saguaro population is large, growing, and healthy. A surge of young saguaros that germinated in the late 1960s through the mid-1990s are thriving. They are growing under “nurse trees” and not yet visible on the landscape, 2) Fewer young saguaros survived and entered the population in the mid-1990s. This slow-down was caused by the lack of ideal environmental conditions for germination and continued through the mid-2000s, 3) More very small saguaros (less than 15 years old) were found. The 1 to 2 inch saguaros were found in foothill and rocky areas of both districts, 4) Saguaros are impacted by the effects of climate change. Saguaros germinate and grow faster during cooler and wetter periods. High temperatures and drought do not allow for germination and cause saguaros to grow more slowly and bloom earlier in the spring, 5) Increased protection of saguaros and efforts to control invasive buffelgrass are working. Since the 1990s saguaros have received greater protection and the removal of invasive plants have allowed more saguaros to grow and germinate. The full detailed analysis of the 2020 Saguaro Census will be published in a scientific journal by Saguaro National Park later this year.

This vital scientific research would not have been possible without our donors who participated in the Adopt-A-Saguaro Program. In addition to grant funds from the National Park Foundation and Western National Parks Association. Thank you for supporting the research and protection of saguaros at Saguaro National Park.