Record High Temperatures in Arizona, Combined with Lack of Monsoon, Place Saguaro Cacti in Desert Botanical Garden Under Severe Stress.
Kimberlie McCue, the scientific director at the botanical garden, stated that the saguaro cactus can appear “quite normal” or slightly soft before it suddenly collapses, revealing that it has been rotting from the inside due to heat-related stress, CNN reported on July 28.
A fallen cactus in the botanical garden. (Photo: KVOA)
Every February, the Desert Botanical Garden conducts an inventory of the saguaro cacti and assesses the condition of each plant. According to McCue, since 2020, when record temperatures have stressed many saguaro cacti, she and her colleagues have noted an increasing number of cacti dying in the garden. The current record temperatures are pushing previously affected cacti to the brink, causing them to shed limbs or even collapse. The evening of July 26 marked the end of a 16-day streak of temperatures above 32.2 degrees Celsius in Phoenix, with the city experiencing temperatures over 43.3 degrees Celsius again on July 27.
Cacti perform many essential functions at night. It is during this time that they exchange gases, absorbing carbon dioxide needed for photosynthesis during the day. However, due to record heat at night in Phoenix, these conditions are suffocating and stressful for saguaro cacti, leading to dehydration and increased vulnerability to diseases and pests. According to McCue, while saguaro cacti are well-adapted to hot and arid environments, they also have their limits.
Phoenix is one of nine cities in the U.S. with at least one million residents living in neighborhoods where temperatures are several degrees Celsius higher than the surrounding areas. In Tucson, temperatures remain above 37.8 degrees Celsius, but local cacti are not experiencing the same stress due to less impact from the urban heat island effect. According to Erik Rakestraw, a plant manager at the Arizona-Sonora Desert Museum, the greatest threat to saguaro cacti is that as temperatures rise over time, new generations of cacti will have a harder time thriving.
