Saguaro Cactus: Sentinel of the Southwest

Background

The saguaro cactus, Carnegiea gigantea, is the largest cactus in the U.S., commonly reaching 40 feet in height. The saguaro provides both food and shelter for a variety of desert species and plays an integral role in the culture of the Tohono O’odham people. It has been written that the saguaro can be ecologically connected to nearly every other organism in its range, including humans.

Saguaro cacti in Saguaro National Park

NPS

Ecology

The saguaro cactus grows only in the Sonoran Desert of the U.S. and Mexico. Its range is limited by freezing temperatures and altitude.

The body and armlike branches of the saguaro are pleated and ridged, with hard spines and bristles. In May and June, white flowers bloom, followed by bright-red fruits that may each contain up to 2,000 small black seeds. Composed mostly of water (75–90% of the plant’s mass), saguaros may weigh more than 6 tons.

Saguaro cacti are highly important to both animals and people. Small birds excavate nest cavities inside the saguaro’s pulpy flesh, and large ones build stick nests among its arms. Saguaro flowers, fruit, and flesh variously provide nectar, moisture, and food for birds, bats, mammals, reptiles, and insects. Archeological evidence indicates that the Hohokam people of the modern-day Tucson area used the saguaro in their daily lives. For the present-day Tohono O’odham, believed to be descendants of the Hohokam, the saguaro is a sacred plant, used for both ceremony and sustenance.

Saguaros are slow-growing. In Saguaro National Park, a saguaro grows between 1 and 1.5 inches in the first eight years of its life; branches normally begin to appear at 50–70 years of age. In drier areas, it may take up to 100 years before the branches appear. Saguaros begin to produce flowers at around 35 years of age, and reach adulthood at about 125 years of age. The average life span of a saguaro is probably 150–175 years, but some plants may live more than 200 years.

Sonoran Desert (brown), with an overlay of the range of the saguaro cactus (green).

Status and Threats

The saguaro is a common plant in the Sonoran Desert, and is not an endangered species. The biggest threats to its current status are anthropogenic: loss of habitat and exotic-plant introduction. Exotic plants, particularly buffelgrass, fountain grass, and red brome, are problematic because they can both outcompete the saguaro and increase the risk of fire in a landscape not adapted to it. Therefore, management of fire and exotic plants in Saguaro NP is crucial to maintaining a naturally functioning saguaro population. Other threats to the saguaro include vandalism, attempted transplant, and theft.

Prepared by Alice Wondrak Biel, Sonoran Desert Inventory and Monitoring Network, 2009.