Saguaro Census 2020

Blog Post by Andrea Hoerr, Cohort 3

On Feb 18 2020, several Pima County Master Naturalists volunteered for the 2020 Saguaro Census. This survey was coordinated by the National Park Service and held at Saguaro National Park West (SAGU) with Don Swann, SAGU Wildlife Biologist, leading the way.

The Saguaro Census is held every 10 years, in concordance with the Federal census. The goal is to survey saguaros in the measurement plot and has been held since 1990. It is a large effort, with an estimated 500 Citizen Scientists participating in the survey. This day, we had 12 Pima County Master Naturalists representing various cohorts. We met at the Visitor Center at 7:45am and carpooled to the location. The participants were broken into groups of 4 and set out to methodically count and measure saguaros.

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What did we do?

  • There was some slow walking involved over the course of 4.5 hours. We took a lunch break around 11
  • The National Park Service staff marked the survey plot before we arrived. Don Swann, Kara O’Brien and Martha were our leaders and knew how to make tromping through the desert fun!
  • Each cactus had a temporary flag attached with a number that was recorded. The names ranged from numbers+letters to names like “Yoda” and “Pretty”
  • The metrics collected were:
    • UTM location – UTM is similar to GPS, but provides more accuracy
    • Height of the cactus. For cactus 6’ and shorter, we used measuring sticks. For taller cactus we learned how to use a tool called the clinometer. The clinometer demanded patience and a certain amount of skill to use effectively. It uses trigonometry to determine the height using a point 10 meters from the cactus, then measuring 2 points on the cactus – the top and bottom. Because it is somewhat fiddley, 2 people measured the height and then averaged the results
    • Number of arms
    • Number of bird holes
    • Any constriction noted which could have been caused by an injury or frost sometime in the history of the saguaro
    • In some cases, the cactus had a permanent tag that was recorded as well as the UTM location
  • Each team of 4 did 3 passes for their section. This was to ensure that no saguaro was missed
  • Laughed and told plant-geek appropriate stories

Overall, it was an excellent volunteer experience which was amazing to share with our fellow Master Naturalists! We each got a 2020 Saguaro Census Survey sticker and bandana which is a fantastic way to acknowledge our contribution.

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Some facts that we learned:

  • Saguaro National Park is around 140 square miles
  • The National Park Service estimates that there are upwards of 20,000 latex balloons littering Saguaro National Park! There’s a scientific journal that was published about this topic. Extract and full article here:
  • Weddellite is a mineral found in dead saguaro skeletons. It is comprised largely of calcite and is a key ingredient of caliche. Fascinating U of A article linked here:
  • We saw a large amount of Merriams kangaroo rat burrows centered around creosote. Sand is blown into creosote and collects into mounds. This provides an excellent opportunity for the kangaroo rat to form burrows.

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