Tucson couple carry out annual saguaro census

Tom Orum, left, and Nancy Ferguson, right, stand under a tree near the Visitor Center at Saguaro National Park in Tucson, Ariz. (Photo by: Ava Garcia/Arizona Sonora News)

For desert dwellers, saguaros are a part of daily life. Scattered in front yards, cropping up along the side of the road, sprinkled on mountainsides, the hulking cactuses are nearly omnipresent in the Arizona desert. We often see them without realizing what goes into the survival of these huge plants that only grow in the Sonoran Desert.

But Tom Orum and Nancy Ferguson focus on just that: How long do these saguaros live, and how many survive each year?

The Tucson couple, both retired University of Arizona researchers, have spent almost four decades conducting an annual census of the saguaros in six plots of land around Saguaro National Park.

Limited by elevation and by freezing temperatures in the winter, saguaros are only found in the Sonoran Desert, according to Saguaro National Park.

Ferguson, 73, said the Sonoran Desert’s combination of both a winter and a summer rainy season, which differs from neighboring deserts with one rainy season, also helps the saguaros get established.

Orum, 70, joined the project, which originally began in 1942, in 1979 as a research technician in the UA plant pathology department. He and Ferguson eventually took over the study in 1999, and the two researchers, who have since retired, keep up the work as volunteers.

“We are kind of stubborn, so we keep after (the study),” Orum said.

Ferguson, who holds a degree in zoology, called herself mainly an animal person but said she is interested in how all the different parts of the ecosystem fit together.

“The thing about a lot of animals is that you can look at them as individuals, and that works for saguaros as well,” Ferguson said. “You know them on a one-to-one basis.”

The couple conducts the yearly census over 12 to 15 days, two hours at a time. Armed with plastic clipboards and a 6-foot-long piece of PVC pipe they nicknamed Charlotte, they follow along a homemade printed map that details the location of each saguaro in the six, 10-acre plots they study. They measure Charlotte against the saguaro and make notes of its height, any holes and any animals that may have made the saguaro a home.

Tom Orum uses a tool he calls Charlotte to measure the height of a saguaro in Saguaro National Park in Tucson, Ariz. (Photo by Ava Garcia/Arizona Sonora News Service)

The real excitement lies in finding new saguaros, usually less than 2 inches tall and sometimes hidden under brush.

““[With the older saguaros] you can sort of synthesize a life cycle, but with these group of new ones you don’t have to,” Ferguson said. “We got them right when they germinated. If somebody picks the study up after us, they will be able to follow through and know very precisely how long they live and under what conditions.”

Over the years, the study has recorded the ups and downs of the saguaro population. From 1942 to 1970, hardly any new saguaros cropped up in the plots, Orum said.

“For a while they called it a saguaro mortality study,” Ferguson said.

Just a few years later, though, the saguaros bounced back: Researchers found new growth little by little in the plots, celebrating each new saguaro they found with a milkshake. Orum said the 1980s were a particularly exciting time, racking up nearly 40 new saguaro finds each year.

Yet the barrenness of the mid-nineteenth century seems to have come around again: Orum estimates the couple has only found about three saguaros across all 60 acres in the last decade.

“At first we didn’t know whether this was real or not,” Orum said. “It took us probably a decade of looking to say, ‘Yep, we’re not seeing them.’”

Orum estimates there are about 60 percent as many saguaros in the plots today as there were in the 1940s. He links this decline back to the population structure of the saguaros, many of which now hover between 35 and 40 years or “middle age,” as Orum puts it. Because of that, not many new saguaros are growing. Still, the population is not decreasing; many saguaros live over a century.

Orum cautions against jumping to conclusions about the decline, recalling the sudden comeback of the saguaros after the 30-year period without new growth.

But weather conditions can affect the establishment of new saguaros. This year was a dry one, and Orum can tell just by looking at the saguaros. The plants are shrunken, their ribs exposed. Reddish coloring, a sign of stress, runs along the base of the saguaros.

The cactus species is tough, able to take on drought stress once mature, but Orum said the concern for long-term drought lies in whether new plants are able to establish themselves.

“The tiny little seedlings are more susceptible to drought stress than the well-established plants,” Orum said.

When it comes to what saguaros face with climate change, Orum and Ferguson said their study can provide a baseline of what is happening now that can be used in comparison to future data.

Orum said the saguaro isn’t the best organism to study for climate change effects because of its high survivability, but he acknowledges that the possibility of extreme drought in the Southwest could impact the younger saguaros’ ability to get established.

“We will see what happens in the next 50 years,” Orum said.

In the meantime, the couple is focusing on their upcoming saguaro census, as well as working on their study on native grass in Cascabel, Arizona. They carry out this study as part of their work with the Sweetwater Center, a conservation non-profit they founded six years ago for their research on agriculture and conservation.

Cindy Salo, a fellow Sweetwater Center board member, has known the couple for decades and has worked with them as part of the Saguaro Juniper Corporation. The corporation owns land in Hot Springs Canyon near the San Pedro River and works together to take care of it.

“(Orum and Ferguson are) good at everything,” Salo said. “They’re very steady, very kind. They’re never in a hurry, but they just get an amazing amount of work done.”

The couple also makes sure to check in on saguaro 650, which Ferguson calls Mom’s Saguaro for her 100-year-old mother who lives in North Carolina. Each year, Ferguson gives her mother an update on her saguaro.

“It’s really to me a gift to be able to know these saguaros as individuals,” Ferguson said. “I don’t know how else I would get the chance to do that.”

Ava Garcia is a reporter for Arizona Sonora News, a service from the School of Journalism with the University of Arizona. Contact her at agarcia9@email.arizona.edu.

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