Photo by Pete Gregoire

Saguaros (Carnegiea gigantea) are the largest cacti in North America -- growing to a height of approximately 50 feet, and often weighing seven tons or more.  Saguaros can be found only in the Sonoran Desert -- southern Arizona, southeastern California, and Sonora, Mexico.

In the early 20th century, the very existence of the giant saguaro cactus in the American Southwest was being threatened . . . and in 1933, President Herbert Hoover used the powers of the Antiquities Act to create Saguaro National Monument -- the first U.S. national park or monument set aside to protect a species of plants.  The saguaro is the tallest cactus in the United States and its distinctive form is recognized worldwide as an icon of the American Southwest.

Saguaros are extremely slow-growing, as a plant may be only six inches high after 10 years, and barely two meters tall after 30 years.

Contrary to popular assumptions, saguaros do not have massive taproots, but rather an extensive network of radial roots that lie mostly within a few inches of the soil surface.  Roots of a mature saguaro can extend 20 meters (65 feet) in all directions from the plant, and can soak up as much as 750 liters (200 gallons) of water in the days following a major rain event -- enough to last an entire year.

Saguaros are very sensitive to cold temperatures;  Tucson is in the northern portion of the species range.  Saguaros here tend to have more spines, especially at the sensitive growing tip to help insulate against the cold.

Extrapolation from saguaro census data taken in 2010 estimates that there are about 1.9-million saguaros within the current boundaries of Saguaro National Park . . . but the species still faces serious threats, as modern-day cactus thieves attempt to poach adolescent plants from public lands.

Saguaro cacti are highly-prized for homes and private businesses throughout Southern Arizona, and cactus rustlers can sell a 6- to 7-foot saguaro for $60 a foot or more;  and last year, some 17 adolescent saguaro plants were stolen from Saguaro National Park itself.

In an effort to deter the poaching, Friends of Saguaro National Park joined with the National Park Service to insert microchip identification tags into more than 1,000 particularly vulnerable saguaros at the Park (adolescent plants in easily-accessed areas).  The chips, about $4 each, are the same kind as those used to identify many pets;  they can be scanned with a special wand (costing between $500 and $3,000 apiece) to provide information about the plant and its location within the Park.  Friends provided the Park Service with necessary funding to begin the microchip identification effort at both the east and west districts of Saguaro National Park -- ensuring the continued protection of these impressive "sentinels of the desert."

Additionally, despite decades of research, there are still many unanswered questions regarding saguaros -- and the Sonoran Desert ecosystem itself is an ever-changing environment.  Researchers are just beginning to address the direct and indirect effects of changes in regional land use, such as urban sprawl in the Tucson Basin.

Continued long-term monitoring projects will be necessary to understand saguaro population dynamics, and how influences such as urban development, global climate change, shifting nurse-plant associations, and epidermal browning may affect saguaro populations in the coming decades.

Scientists also continue to study the potential impact of invasive plant species (such as buffelgrass) on the natural fire regimes of the Sonoran Desert;  most believe that any major fire in the Sonoran Desert ecosystem would be catastrophic for the saguaro cacti and the wildlife (such as Sonoran Desert tortoises) that depend on native forbs and grasses for survival.

You can help protect the saguaros at Saguaro National Park by donating to the Friends of Saguaro Adopt A Saguaro program;  all proceeds go to saguaro protection and research projects -- as we attempt to ensure the conservation of these impressive "sentinels of the desert."