The mighty saguaro cactus is both a cultural and ecological icon. Crimson fruits open and drop preceding the monsoon season providing sustenance for desert life at the hottest, driest time of the year. The tall cacti cast shade, creating patches of microclimates that make life more possible in the arid desert.
Despite being a strong foundational species, saguaros need a little help as sprouts. A small plant can easily dry out or freeze in the harsh Sonoran Desert. In many plant communities, one species can support the survival of another, a process known as facilitation. Saguaro “nurse” plants such as mesquite, palo verde, and even other cacti provide shade, reduce temperatures, diminish wind, protect seedlings from predators, and add nutrients to the soil.
In Sonora, Mexico, researchers found 83 saguaros growing under a single mesquite tree. Saguaros may even establish near “nurse rocks” that re-radiate heat at night, increasing nighttime temperatures.
Indigenous peoples, including the Tohono O’odham, have long recognized the importance of nurse plants facilitating saguaro growth. Anthropologist Ruth Underhill recorded Tohono O’odham elders comparing young saguaros to sick children: the plants struggle to grow on their own, while fast-growing palo verde trees act like mothers, providing shelter and resources.
In the summer months, birds, bats, mammals, and insects consume saguaro fruit under the shade of viable nurse plants, starting the dynamic cycle over again.
This Earth Note was written by Danika Thiele and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.
