ALIVE AND WELLTHANKS TO BAD SCIENCE, RUMORS OF THE SAGUARO'S DEMISE HAVE BEEN GREATLY EXAGGERATED
Despite what you might have heard or read, the giant saguaro cactus is not dying off. There are plenty of genuinely endangered environmental victims around this big, bad world, but Carnegiea gigantea isn't one of them.
Joe McAuliffe, director of research for Phoenix's Desert Botanical Garden, makes that point in a sometimes scathing new case study done for the National Park Service.
McAuliffe reviewed more than 50 years of research and management techniques at Saguaro National Monument. His report, a critique of essentially all of the most significant scientific work ever done on the saguaro cactus, lays waste to a lot of it as "bad science," and contradicts the prevailing notion that the saguaro cactus is doomed to extinction. "I'm always getting calls from Newsweek reporters, or the New York Times, saying, 'We've heard the saguaros are dying,'" says McAuliffe, who taught at the universities of Arizona and Nevada-Las Vegas before joining the botanical-garden staff three years ago. "One day it's disease. The next day I get a call saying, 'We've heard that the growing ozone hole is causing the saguaros to disappear.'
"Mistakes in saguaro research have created so much misunderstanding, I think the only way to cure it is to start swinging a hatchet." McAuliffe targets research done at the monument, founded near Tucson in 1933 to protect and showcase what was then an awesome stand of mature, multilimbed saguaros. It was a spectacular "cactus forest" unlike any other in the Sonoran Desert in Arizona and Mexico, the plant's only natural habitat.
To date, a majority of that research has been focused on one disturbing trend: Saguaro National Monument's population of big saguaros has been visibly declining for more than 50 years. Worse, the dying saguaros have not immediately been replaced with other equally impressive plants. Of course, saguaros and the concept of "immediately" don't mix: The life span of a healthy saguaro is more than 150 years. Five-year-old plants are about the size of a human thumbnail, and the cactus doesn't begin to reproduce until about age 50 or sprout arms until about age 65. In most saguaro experiments, the subject outlives the scientist, and research started this decade will only begin to have much relevance in about 2100. As the monument's older saguaros have gradually dropped dead, the aesthetic effect has been devastating: Sequential photographs dating to the 1930s appear to illustrate a mass extinction.
McAuliffe swings his hatchet most forcefully at early researchers who blamed the apparent die-off on a mysterious bacterial disease, and later scientists who tried to blame more contemporary environmental woes. Their theories and resulting experiments, he says, were poorly conceived and executed, yet received inordinate publicity.
And the public, already prone to overromanticize the plight of the saguaro, has been misled about the plant's true status, which is, McAuliffe says, actually quite healthy. "Unfortunately, the worst research always gets put up on the tallest pedestal," he says. @rule:
@body:The first bad round of research, McAuliffe says, resulted in the misdiagnosis of a deadly saguaro mystery disease in the late 1930s and early 1940s, about the same time that the saguaro ranks were beginning to thin. That's when a scientist from the UofA decided that the big cactuses were dying because of a "blackening necrosis"--a trunk discoloration that eventually turned to rot--caused by the bacterium Erwinia carnegieana. This theory prompted years of "disease suppression experiments" at the monument. In one test, affected plants in a 320-acre area were removed (by dragging them out of the ground using cables attached to trucks), disinfected with chemicals including kerosene, then buried in a mass grave. In other experiments, antibiotic treatments were applied to the sick saguaros, which were also doused with pesticides after it was discovered that a species of moth was spreading the "disease."
By the early 1960s, researchers who followed up on the preliminary disease work were predicting that the monument's saguaro forest would be wiped out by the turn of the century.
Nuts, McAuliffe concludes: The disease hits cactuses that have already been damaged by cold weather. The midcentury die-off of mature, many-armed saguaros--the seeming catastrophe that prompted so much concern--was actually caused by a hard freeze in 1937. Saguaros are most vulnerable to weather extremes when they're either very young or very old. Many of the big plants that made up the Cactus Forest in 1940 had sprouted during the mid- to late-1880s--due to extra-heavy rainfall, a meteorologically sublime time for young saguaros--and managed to survive a severe freeze in 1913 because they were then in their sturdy years of late middle age. But the big chill of 37 nipped them, then the bacteria went to work, McAuliffe asserts. Subsequently, scientists spent decades battling a plant disease that struck saguaros that were already dying. And deep freezes near the turn of the century explain why so few mature cactuses are with us now: They didn't make it out of puberty. @rule:
@body:Some contemporary research at the monument has been no more enlightened than the earlier black-tissue work, according to McAuliffe, who is critical of recent experiments done by the National Park Service's Denver-based Air Quality Division.
AQD attempted in the past few years to pin saguaro mortality on two different culprits: air pollution from Tucson and nearby smelters, or increased ultraviolet radiation caused by a hole in atmospheric ozone.
Nuts again, McAuliffe says in his report, which lambastes the conceptual foundation of AQD's work, as well as its execution of experiments, one of which involved a New York City academic who used baling wire to string a fluorescent light bulb between cactuses to study the effects of UV radiation. McAuliffe all but charges the air-quality folks with jumping on the cactus bandwagon in hopes of using the sexy saguaro to make a point about air-pollution laws. "None of the information provided by the Air Quality Division stands up to scrutiny," says McAuliffe. "That was a program driven, I think, more by the politics of air-quality regulations rather than a careful consideration of where the problems really are. "I think those are very important laws, and necessary laws. Unfortunately, the saguaro is such a charismatic creature, it's grabbed on to and used to further political ends."
Today, all experiments on the effects of air pollution and UV radiation on the monument have stopped. One top air-quality official says the air-pollution experiments should be judged successful because they failed to show any relationship between saguaro mortality and bad air--and because they did show some minor air-pollution damage to ponderosa pine in the higher elevations of the monument. "It was very light injury, nothing catastrophic [among ponderosas], but there was some suggestions of further research, maybe some follow-up surveys," says Mark Scruggs, chief of the research branch at the Air Quality Division. "I think that's probably worth doing someday."
As for McAuliffe's charges that the air-pollution studies were flawed at conception--that there was no real evidence to even begin the experiments in the first place--Scruggs says: "I guess our position all along was, 'We aren't sure.' But the saguaro was important enough that if there's a possibility that air pollution might've been a contributor to decline, it was worth doing. "And if at the end of your studies, you find that, well, maybe it wasn't a component, at least we've ruled out one possibility."
But what about all those doomsday stories about the demise of the saguaro? McAuliffe charges that air-quality-division researchers sometimes sought premature publicity for their unproven theories. Scruggs deflects such criticism by saying that the very nature of AQD research, coupled with the saguaro's mythic appeal, caused overheated media interest. "There was a lot of publicity along the way as our studies were progressing," he says. "I guess the very fact that you have air-quality specialists doing work someplace leads people to believe that we had some reason to suspect that air pollution was having some effect on the monument."
@body:In addition to irregular temperature dips, McAuliffe lists several more explanations for the big-cactus loss at the monument. Most of them are considerably less exotic than mysterious skin-blackening diseases, smog or sunburn.
For example, McAuliffe says cows are partly to blame for the current paucity of middle-aged saguaros.
Cattle were allowed to wander the monument until the late 1950s (amazingly, the park service didn't wholly own all the land until then) and likely trampled plenty of young saguaros.
Saguaro seeds take root under the shade of "nurse trees"--typically paloverde or mesquite--which protect the seeds from summer sun and winter frost. "On a hot June day, that's where cattle hang out," McAuliffe says. "They lay under those trees and chew their cud." Photos from the 1930s offer another piece of the die-off puzzle: Though the population of mature saguaros appears robust, the "nurse-tree" population is next to nonexistent. As homesteaders and other settlers harvested desert trees for firewood, they also eliminated the important shrub canopy that protected saguaro seedlings. Finally, the park service actually wielded little security control over the monument for the first several decades of its existence. Until 1958, the UofA and private homesteaders owned significant pieces of what is now monument land. McAuliffe cites one amazing report filed by an early monument superintendent which details a raid conducted on the cactus forest by crews employed by Columbia Pictures, probably sometime in the 1930s. The raiders swiped whole saguaros and hauled them away. "[The superintendent] described them as not being excavated, but rather sawed off at the base," says McAuliffe. "I suspect they may have been filming somewhere in town where there weren't any saguaros, and they needed them as props."
@body:The saguaro world will not immediately unite behind McAuliffe and his conclusions. "What the hell has he ever done for saguaros?" grumbles one of the researchers criticized in McAuliffe's report. "I wasn't sitting back in some easy chair in a botanical garden intellectualizing about these things. I was trying to figure out what was going on."
Meg Weesner, chief of science and resources management at Saguaro National Monument, says McAuliffe is not alone in questioning some of the previous research, and adds that the Park Service plans to organize the first big symposium of saguaro scientists for next fall in Tucson. The group will discuss "what's known so far" and ask "what are the next things we need to know?" says Weesner. "There's an awful lot of concern about the future of the saguaro."
McAuliffe is careful not to overgeneralize. "The monument is not the whole story of saguaros," he says. "That's just the very tip of the species." But he will say that this cactus-research story, at least as it applies to the cactus in Saguaro National Monument, has a happy ending. "The saguaro is not going extinct, not declining on a wholesale basis because of any mysterious malady or because of air pollution," he says. "The saguaro population is not declining in Arizona or in Sonora, Mexico. The population that did locally decline at the Saguaro National Monument is rebounding now. There are many, many young saguaros, most not even knee-high yet, that are someday going to be another saguaro forest.
Get the ICYMI: Today's Top Stories Newsletter Our daily newsletter delivers quick clicks to keep you in the know
Catch up on the day's news and stay informed with our daily digest of the most popular news, music, food and arts stories in Phoenix, delivered to your inbox Monday through Friday.