Scientists “Listen” to Saguaros — Seismic Vibrations Reveal Daily Changes and Offer a Non‑Invasive Health Check

Seismometers reveal subtle daily rhythms in Arizona’s iconic saguaros

Arizona’s towering saguaro cacti, long seen as still sentinels of the Sonoran Desert, actually vibrate in response to wind, environmental forces and distant seismic energy. Researchers have adapted geophysical instruments used to measure rock and earthquake vibrations to record those subtle frequencies, creating a non‑invasive way to probe a cactus’s internal structure.

A University of Utah geologist, Moore, developed the technique by repurposing ambient vibration seismology—the tools and analysis methods commonly applied to rock arches, towers and earthquake signals. The research, published last month in the American Journal of Botany, demonstrates how vibration data can provide insight into a cactus’s structural properties without cutting or harming the plant.

How the study was done

With permission from Pima County, Moore worked in Tucson Mountain Park, a 20,000‑acre preserve adjacent to Saguaro National Park. He selected tall, single‑column saguaro "spears" and carefully strapped lightweight seismometers to them. Each cactus was recorded for roughly 15 minutes, and the study sampled 11 individual saguaros of varying heights.

Key findings

The measurements showed that each saguaro’s resonance frequencies shifted over the course of day and night. Those shifts suggest the cactus’s outer skin or cortex becomes alternately stiffer and more flexible on a roughly 24‑hour cycle. Moore initially expected short‑term changes to be driven mostly by water content, but the vibration records indicate a more complex pattern of daily mechanical change.

"One of my main tools is ambient vibration seismology to study rock structures, like arches and towers. I realized those measurement and analysis techniques could be applied to biomechanics," Moore said. "The daily shifts in the cactus cortex are clearly detectable, though the exact biological mechanism needs further study."

Why this matters

Saguaros are a keystone species in the Sonoran Desert, providing shelter and food to birds, bats, insects and other wildlife. They are protected under Arizona state law; harming, moving or killing a saguaro without a permit is illegal. At the same time, saguaro populations face growing threats from rising temperatures, prolonged drought, wildfires and nonnative animals such as burros that damage the young plants' shade and nursery habitat.

Monitoring structural health without invasive sampling is therefore urgent. The new seismic technique offers land managers and ecologists a potentially fast, repeatable and non‑destructive tool to assess cactus condition and detect early signs of structural decline.

Next steps: Researchers plan to expand measurements across seasons and hydration states, compare vibration signatures with internal anatomy and explore automated monitoring systems that could track saguaro health over time without disturbing these culturally and ecologically important plants.

Reporting was supported by environmental coverage grants. For more information, see the original study in the American Journal of Botany and local conservation updates from the Arizona Game and Fish Department and Desert Botanical Garden.