You are here

Share
All that remains of what once was thought to be the world's largest saguaro/NPS

Editor's note: When the renowned Freeman Tilden, whose name is carried on an award the National Park Service bestows each year to an outstanding park interpreter or educator, first visited Saguaro National Monument, as it was known at the time, he recognized the human threat encroaching on the monument: "The great saguaro forest near Tucson is possibly a doomed forest. It is not renewing. True, it will be there for many years. But civilized human life moved in upon it." Add to that human crush ever-expanding from Tucson the impacts of climate change, and it's clear Saguaro deserves a place on National Parks Traveler's 3rd Annual Threatened and Endangered Parks list.

The vast, arid landscape of Saguaro National Park is often simply characterized as a desert. While it’s true that the park lies within the formidable Sonoran Desert where summer temperatures reach north of 115 degrees, the land between park boundaries teems with life and hosts complex habitats.

With 1.6 million saguaro cacti, the National Parks Conservation Association calls Saguaro National Park “the largest forest of its kind on the planet.”

“It almost doesn’t qualify as a desert because it gets enough precipitation that it grades into what’s called a subtropical thorn scrub forest,” notes Tice Supplee of Audubon Southwest.

Or, at least, that has been the case, historically.

Today, numerous species living there, including the signature cactus, face many challenges — urban development, invasive species, drought and wildfires amplified by climate change, rank among the most-pressing.

Saguaro's Unique Biodiversity

Saguaro is unique in that it has two distinct units. Together, they straddle the rapidly growing city of Tucson, Arizona, to the east and west, span more than 140 square miles, and range in elevation from approximately 1,000 feet to 8,500 feet above sea level.

When it was alive, "Granddaddy" was thought to be the world's largest cactus. Lost to old age in the 1990s, all that remains is its downed skeleton (title photo)/NPS filese

When it was alive, "Granddaddy" was thought to be the world's largest cactus. Lost to old age in the 1990s, all that remains is its downed skeleton (title photo)/NPS file

At various altitudes, Northern Goshawks and whiskered screech owls patrol the air. Roadrunners, Gila monsters, kangaroo rats, and collared peccaries scramble between acacia and palos verdes trees, oak woodlands, and creosote bushes. Cactuses of all imaginable shapes and sizes stretch their spiky arms toward the sky— agave, yucca, prickly pear, and, of course, the saguaro.

A mature saguaro cactus is unmistakable. Some grow to be 60 feet tall and weigh more than a ton. The silhouette of its outstretched arms is emblematic of the American West. It is the park’s signature attraction and a big reason why Congress elevated this dynamic region of the Sonoran Desert in southern Arizona to national park status in 1994.

But the story doesn’t end there.

More than 25 years later, the saguaro cactus, as well as lesser-known plant species and critters who call the park home, are threatened and may require additional protection. Officially, the Southwestern willow flycatcher is the only endangered species that lives in the park, according to the U.S. Fish and Wildlife Service, while the Yellow-billed cuckoo and Mexican spotted owl are listed as threatened.

“The lesson is national park status is not the end of one’s work protecting that area for its resources and for its visitor experience,” said Kevin Dahl, the NPCA’s former senior program manager for Arizona and a recently elected Tucson city councilmember. “There will be threats from outside or activities inside the park that are inappropriate that citizen activists need to be able to help stop or change.”

Strangled By Urban Development

Among the threats Dahl mentions is Interstate 11, a proposed highway that would run from Canada to Mexico through Pima County, which envelops Tucson and both units of Saguaro National Park. 

Proponents of I-11 say it would enhance travel and promote job growth and economic competitiveness. The NPCA has said I-11 would have devastating and irreversible” impacts on Saguaro National Park and surrounding desert ecosystems.

The debate over where to place the route goes back several years because of environmental concerns.

Audubon Southwest advocated against prior iterations of highway plans that it said would disturb the Joshua Tree Important Bird Area in Mohave County and the Lower Salt and Gila Rivers Important Bird Area in Maricopa County.

As of yet, the Arizona Department of Transportation has not finalized plans for the interstate near Tucson. 

A proposed interstate highway threatens Saguaro National Park's wildlife/Arizona DOT

Currently, the Arizona Department of Transportation is considering two corridor options through Pima County: an east option and a west option. Either plan would then have to undergo additional environmental studies, which have not yet been scheduled or funded, Laura Douglas, ADOT communications manager, told the National Parks Traveler in an email.

Supplee says a transportation corridor for vehicles west of the city in the Tucson Mountains could squeeze vital wildlife corridors for large mammals like lions and deer.

“The western segment of the park is getting surrounded by people,” Supplee said. “It’s the larger vertebrates that take the pressure (of development) first.”

She added that a similar cycle of urban development led to the demise of bighorn sheep in the region as far back as the 1960s. Other researchers say human development led to a decline in local bighorn sheep populations starting in the late-1970s or 1980s.

The Tucson metro area has grown steadily since then and now hosts approximately one million residents.

All that growth requires more development, which often encroaches on what had been natural habitats. Last year the Arizona Daily Star reported that 1,400 apartment units were under construction at nine sites around Pima County, and another 1,600 units were in the planning stages. Meanwhile, local rents increased 7.1 percent from last year, compared to 5.2 percent for Arizona as a whole, according to Apartment List data.

Dahl says the specter of development has been a threat to the Tucson Mountains since they were homesteaded and mined long before any part of the range was incorporated into a county park and later a national monument and finally a national park.

“The issue of having a wilderness park with urban interface is something that the park has to deal with,” Dahl said.

Invasive grasses: “The archenemy of the Sonoran Desert”

It’s a newer threat that’s most concerning to Supplee. She says an “unnatural” fire cycle in the park fueled by invasive grasses and drought-stricken conditions endangers sensitive habitats:

“Should we end up with an unnatural fire cycle in the park, we could lose the iconic saguaro and palo verde plant community. It could be replaced by a desert scrub grassland, and it could be many, many generations before you would see saguaro again because they’re so slow-growing,” Supplee said.

At lower elevations in the park, historically fire played almost no role. The sparse grasses and forbs in the desert rarely allowed fire to spread, according to the National Park Service.

But in recent decades, several species of invasive grasses that thrive in dry climates throughout the world have overrun the park, covering the sandy desert floor like a flammable carpet.

Nonnative buffelgrass is a key threat to Saguaro's ecosystem/NPS file

Buffelgrass, native to Africa, Asia, and the Middle East, arrived in the United States in the 1930s and was widely planted around Tucson for erosion control in the 1970s and 1980s. It has since proliferated across southern Arizona.

The U.S. Geological Survey says buffelgrass “has the potential to transform the Sonoran Desert ecosystem from a diverse assemblage of plants to a grassland monoculture.

The National Park Service calls buffelgrass “the archenemy of the Sonoran Desert — the invasive grass most likely to cause significant damage to the native ecosystem.” 

In fact, Park Service ecologists in 2010 estimated that fires in the park would increase in size and intensity because non-native grasses at that point already ranged from two times to 4,000 times usual Sonoran Desert fuel loads.

“Damage from wildfires will be unprecedented,” two ecologists wrote in a 2010 document.

So far, Saguaro has largely been spared from severe fire, but nearby Tonto National Monument has not. The human-caused 2019 Woodbury Fire burned through swathes of red brome, another invasive grass, and killed saguaro cactus and other native species “in huge numbers,” NPS ecologist Andy Hubbard told the Traveler last summer.

“The surrounding area looks like a moonscape,” he said.

The Spectre Of Climate Change

The bloom of invasive grasses contrasts with an unusual reproductive behavior displayed by many saguaro cactus. Some are flowering off-season or hardly at all. Hubbard suspects this might have something to do with rising winter temperatures and drier soils, and those same drought-like conditions might play a role in the diminishing number of young saguaros that have reached reproductive age since the mid-1990s.

The Sonoran Desert typically receives more rain during its summer monsoonal season than in the winter. 

“Winter rains play a role but are not as key,” Supplee said.

However, seasonal weather patterns are becoming more volatile.

According to the Park Service, winter minimum temperatures within the park have risen 10-15 degrees Fahrenheit in the last 100 years. When it comes to precipitation, even less rain has been falling in the winter, and more rain is occurring during the monsoon season.

The Park Service says highly variable or extreme weather makes it difficult for the saguaro cactus to survive and the effect on other species is difficult to predict.

Reason For Hope

Research on saguaros in the park began as early as 1939; Saguaro had been a national monument since 1933. By 1962, some researchers were predicting that saguaros would be gone by the year 2000 from what later became the eastern park unit. After that ominous forecast, many factors changed favorably for the cactus — factors that were directly controlled by humans.

Since the 1960s, cattle grazing and wood-cutting declined in areas where saguaro nurseries thrived. In 1994, the federal government elevated Saguaro as a national park.

It can take a decade or more for young saguaro to grow large enough to be noticed by the casual observer. And in recent years, the recruitment of saguaro young has tapered off/NPS file

While saguaros seem to be hanging on, the evidence is mercurial.

The park's 2020 Saguaro Census found that "[S]ince 1990 the number of saguaros has nearly doubled, from an estimated 1.15 million in 1990 to 2 million in 2020."

At the same time, however, "it is clear that the surge of new saguaros entering the population in the late 20th century has now mostly ended. In 2020 we detected only slightly more saguaros than in 2010. We did find some younger plants in foothills and slopes of both districts, where certain soils and rock crevices may retain moisture for longer than in lower, flatter areas," the census report states. "We attribute the overall decline in survival of young saguaros to extended drought that began in the 1990s and appears to be driven by higher temperatures."

All might not be lost, though. In December 2020, Congress expanded the park’s area by 1,152 acres as part of the Consolidated Appropriations Act of 2021.

Perhaps, another wave of environmentally-conscious decisions about where to build housing and highways and how to abate invasive grasses and unnatural fires will lend itself toward a resurgence of saguaro cactus and the Sonoran ecosystem.

“There’s good work to be done,” Supplee said.

Support National Parks Traveler

National Parks Traveler is a small, editorially independent 501(c)(3) nonprofit media organization. The Traveler is not part of the federal government nor a corporate subsidiary. Your support helps ensure the Traveler's news and feature coverage of national parks and protected areas endures. 

EIN: 26-2378789

A copy of National Parks Traveler's financial statements may be obtained by sending a stamped, self-addressed envelope to: National Parks Traveler, P.O. Box 980452, Park City, Utah 84098. National Parks Traveler was formed in the state of Utah for the purpose of informing and educating about national parks and protected areas.

Residents of the following states may obtain a copy of our financial and additional information as stated below:

  • Florida: A COPY OF THE OFFICIAL REGISTRATION AND FINANCIAL INFORMATION FOR NATIONAL PARKS TRAVELER, (REGISTRATION NO. CH 51659), MAY BE OBTAINED FROM THE DIVISION OF CONSUMER SERVICES BY CALLING 800-435-7352 OR VISITING THEIR WEBSITE WWW.FRESHFROMFLORIDA.COM. REGISTRATION DOES NOT IMPLY ENDORSEMENT, APPROVAL, OR RECOMMENDATION BY THE STATE.
  • Georgia: A full and fair description of the programs and financial statement summary of National Parks Traveler is available upon request at the office and phone number indicated above.
  • Maryland: Documents and information submitted under the Maryland Solicitations Act are also available, for the cost of postage and copies, from the Secretary of State, State House, Annapolis, MD 21401 (410-974-5534).
  • North Carolina: Financial information about this organization and a copy of its license are available from the State Solicitation Licensing Branch at 888-830-4989 or 919-807-2214. The license is not an endorsement by the State.
  • Pennsylvania: The official registration and financial information of National Parks Traveler may be obtained from the Pennsylvania Department of State by calling 800-732-0999. Registration does not imply endorsement.
  • Virginia: Financial statements are available from the Virginia Department of Agriculture and Consumer Services, 102 Governor Street, Richmond, Virginia 23219.
  • Washington: National Parks Traveler is registered with Washington State’s Charities Program as required by law and additional information is available by calling 800-332-4483 or visiting www.sos.wa.gov/charities, or on file at Charities Division, Office of the Secretary of State, State of Washington, Olympia, WA 98504.
Featured Article

Comments

So do both proposed I-11 routes hurt Saguaro or just the West route?


Primarily the west route.  It would have many other harmful impacts as well.


Add comment

CAPTCHA

This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

Image CAPTCHA
Enter the characters shown in the image.