Abstract Windthrow is a significant disturbance in many forests globally during which strong winds damage trees or other large flora, yet its role in arid ecosystems remains largely understudied. The saguaro cactus ( Carnegiea gigantea ), a keystone species of the Sonoran Desert, is a long‐lived, massive succulent whose demography is primarily thought to be influenced by mortality from drought, freezing, wildfire, and disease. Here, we document a large‐scale windthrow event initiated by a localized microburst on 22 August 2023 in Saguaro National Park, Arizona, USA. We mapped 1789 dead and 537 damaged saguaros across a 473‐ha area. Meteorological and radar analyses confirmed the microburst's signature, revealing a localized downburst with strong, divergent surface winds (approximately 10 m s −1 gusts, likely >45 m s −1 downdrafts), rapid temperature drop (16.4°C), and intense rainfall. Our surveys revealed disproportionately higher mortality among taller, mature individuals (>3.65 m in height). Most uprooted saguaros fell west‐northwest (WNW), consistent with the storm's trajectory. A notable finding was delayed mortality among most individuals impacted, with more than half of the recorded deaths occurring months post‐storm. We hypothesize this delayed mortality resulted from root damage sustained during the initial wind event, impairing water uptake. While windthrow is an infrequent disturbance for saguaros, the measured mortality rate owed to this microburst was 7% for mature individuals, greatly exceeding the background annual mortality rate (1.65%). This event highlights windthrow as a rare but demographically significant disturbance for saguaros, emphasizing the vulnerability of these keystone desert plants to intense convective storms, which may increase in frequency under changing climate. Our results underscore the need to incorporate stochastic wind disturbance into long‐term demographic models of desert plant populations.
Swann et al. (Fri,) studied this question.