Across Arizona and much of the Southwest, the saguaro cactus is admired for the way it thrives in the desert.
Saguaros are the largest cactus in the United States, and can only be found in the Sonoran Desert. These iconic green giants can grow up to 40 feet tall and live for more than 150 years. They are well-equipped to survive droughts by absorbing and storing rainwater.
Saguaros can grow several arms, sometimes curled but often raised, in a never-ending manner of greeting residents and visitors. Arizona law protects the plant. The native Tohono O’odham tribe treasures it. And several schools, businesses, and organizations use its name.
But a changing landscape—one which is growing increasingly hotter and drier—are raising concerns about the saguaro’s ability to survive in the Sonoran Desert.
Desert Botanical Garden, nestled in the buttes of Papago Park, is working to save these treasured desert plants and many others from natural and human-caused threats. Though visitors might be familiar strolling the Garden’s trails or attending holiday events like Las Noches de las Luminarias, they might be surprised to learn about the research and conservation projects that happen here.
That includes saving the beloved saguaro.
“Our iconic plant is really threatened right now,” says Steve Blackwell, conservation collections manager at the Garden.
As wildfires blaze across Arizona, including the Telegraph Fire near Superior that burned more than 180,000 acres in June, the saguaro faces a serious threat. Wildfires can kill hundreds of them as the fire spreads.
The Garden’s Ahearn Desert Conservation Laboratory, which opened in September 2019, is instrumental in preserving desert plants. Garden researchers can photograph, test, preserve, and germinate seeds of rare, threatened, or endangered species. If certain populations of plants diminish, researchers can use stored seeds in restoration projects to grow more plants and safely place them back into the wild.
The facility was built after a generous donation from volunteer Susan Ahearn and her husband, Bill.
“We use the seed bank in the seed lab as kind of our insurance policy against extinction,” Blackwell says.
Cacti are the fifth most endangered organism in the world. Without these prickly desert plants, wildlife would lose a vital source of food and habitat, and the Sonoran Desert would look remarkably different if these plants went extinct.
Since the early ’80s, the Garden has been collecting and maintaining seeds of rare, threatened, and endangered plant species as part of a national network of botanical gardens that founded the Center for Plant Conservation.
But collecting seeds might be the easiest part for Garden researchers. Learning how to germinate seeds is trickier, Blackwell says.
Some seeds only grow under certain environmental conditions.
The endangered Arizona eryngo lives in a specific type of wetland in southern Arizona, called ciénagas. The plant is imperiled due its loss of habitat. Garden researchers were interested in restoring the population, and set out to grow these plants at the facility. But they were surprised when their first attempt produced little results.
“About 5% were germinating,” Blackwell says.
After a series of tests, researchers discovered that the number of Arizona eryngo seeds sprouting increased when given a period of cold, moist conditions. The outcome allowed the Garden to grow hundreds more of these plants for reintroduction back into the wild, while also collecting their seeds for future conservation efforts.
“That’s kind of our ideal goal,” Blackwell says about the restoration project.
“There are so many uses. We are still finding out all the time what we can do here,” he says, referring to the Garden’s facility. But the Garden’s research and conservation work doesn’t stop there.
Five years ago, the Garden set out to help restore the monarch butterfly’s shrinking population through its Great Milkweed Grow Out initiative.
Monarchs exclusively use milkweeds to lay their eggs, and through this initiative, Garden researchers learn more about how monarchs and other insects use milkweed. The project works to increase availability of native milkweed and nectar plants in order to increase monarch and pollinator habitat in the urban community and wildlands.
Over the years, monarchs have faced a loss of habitat due in part to development and herbicides that kill milkweed and nectar plants.
Fewer than 2,000 monarch butterflies were counted this year on the coast of California, representing a 99.9% decline of the western population since the ’80s, according to the Monarch Joint Ventures, a St. Paul, Minnesota-based nonprofit focused on conserving monarchs. The eastern population also is facing consistent decline.
Though the plant is toxic to other creatures, monarchs use the toxins inside milkweed as a form of protection against predators.
“When the caterpillars eat the plant, they ingest the toxin, and it makes them distasteful to predators,” says Natalie Melkonoff, plant and insect ecology program coordinator at the Garden. “Monarch caterpillars and butterflies are brightly colored, and that serves as a defense—a warning coloration that advertises to predators they are not worth eating.”
Arizona has about 30 species of milkweed, the second highest milkweed diversity in the U.S. But very little is known about how monarchs use these plants, Melkonoff says. Garden researchers are studying which species of milkweed are best to support monarchs.
“There seems to be a sweet spot between not enough toxin to sequester as a defense and too much that inhibits growth and development,” she says.
Melkonoff also is studying how climate might affect milkweed, and how those changes might influence monarchs.
“If there are extreme droughts or heat events, do those change how the plant is producing toxins? How is the plant regulating its own physiological function, and what are the trade-offs that impact how the monarch is using the plant,” she says.
Increasing milkweed and native nectar plants are a couple things Arizona residents can do to support monarchs and create healthy urban ecosystems, Melkonoff says.
“Arizona is an interesting spot, with so many milkweed species and monarchs from both the western and eastern flyways, to do monarch conservation,” she says.
The Garden, since its founding in 1939, has served as a premier destination for research and conservation of desert plants and habits. Garden researchers collaborate with academic, research, and conservation groups from across the world on a variety of projects, including the discovery of new plant species, conservation of threatened and endangered species, and identifying potential threats to desert habitats throughout the world. All admissions revenue the Garden collects helps fund work like the seed lab, the Great Milkweed Grow Out, and many other projects. For more information, visit www.dbg.org.