The Sonoran Desert is the only area where the iconic Saguaro cactus grows. The Desert covers southern Arizona and the State of Sonora in Mexico. The California Sonoran habitat is limited to the Whipple Mountains, and Imperial County has only 30 Saguaro specimens.
Saguaro is tree-like and can reach heights of 40 feet; it is a desert keystone species providing critical habitat, protection, and food for desert species. The cactus requires water to grow; in the dry Tuscon area, the cactus takes twice as long to develop as in other Sonoran ecosystem regions. But the monsoon rains do not fall as consistently as they have before. Today the monsoon is delayed, and the towering cactus has begun to collapse and die. Others have lost limbs are leaning due to the weeks-long heat wave with temperatures above 110 degrees for 25 days. An even hotter heat dome is due to arrive next week.
Cacti that suffer from prolonged heat, like what's being seen in Arizona right now, could take months or even years to die, Reuters reported.According to reporting by Insider, "McCue — who, along with her team, assesses the Botanical Garden's cacti each February — told CNN that she has been seeing more death among the Arizona saguaro cacti since 2020 when record highs caused the plants to undergo stress." Phoenix's urban heat island effect is not surprisingly lethal to many cactus.
A significant problem for Saguaro survival is that the plant cannot cool down as it has in years past due to record-breaking nighttime temperatures and monsoon delays. To paraphrase paleoclimatologist Peter Brennan, we have entered a new climate that will be punishing in the short term and the long term.
The Sagauro lifespan is up to 175 years, but that is changing as the species is not as adaptable to drought, monsoon disruption, and increasing blistering temperatures due to human-generated greenhouse gases as many assume.
When looking at natural systems, it is essential to note that plants and animals have never evolved in temperatures this hot. The heat crisis is the new normal that only worsens until equilibrium is reached.
Heat is the culprit for rainfall pattern disruption in deserts. Researchers are seeing increasing heat stress with animals, where organisms attempt to adapt to a world without precedent.
PHOENIX, July 25 (Reuters) - Arizona's saguaro cacti, a symbol of the U.S. West, are leaning, losing arms and in some cases falling over during the state's record streak of extreme heat, a scientist said on Tuesday.
Summer monsoon rains the cacti rely on have failed to arrive, testing the desert giants' ability to survive in the wild as well as in cities after temperatures above 110 degrees Fahrenheit (43 Celsius) for 25 days in Phoenix, said Tania Hernandez.
"These plants are adapted to this heat, but at some point the heat needs to cool down and the water needs to come," said Hernandez, a research scientist at Phoenix's 140-acre (57-hectare) Desert Botanical Garden, which has over 2/3 of all cactus species, including saguaros which can grow to over 40 feet (12 meters).
Plant physiologists at the Phoenix garden are studying how much heat cacti can take. Until recently many thought the plants were perfectly adapted to high temperatures and drought. Arizona's heat wave is testing those assumptions.
Saguara can survive an infrequent fire, but like extreme drought and heat, the plants did not evolve with wildfire. The fragile habitat was further disturbed by the introduction of invasive non-native grasses providing the fuel to incinerate the shallow root system of the Saguaro. They will not survive that kind of damage from wildfire.
Around July, monsoonal summer storms roar into the Sonoran Desert from Mexico, bringing about half of the region’s annual precipitation—along with lightning. Historically, lightning would have ignited a few fires in the Sonoran Desert. They were infrequent and small, because the desert had little fuel for burning. “You would get a lightning strike, it would burn up a little chunk, and then it would go away,” says Lata.
Today, the non-native grasses that grow in a knee-high carpet between the shrubs and cacti act as fine fuels—kindling—to carry fire in a new way. The Bush Fire started in 2020 when an overheating vehicle pulled off the road and the brakes sparked roadside grasses. Wind and dry conditions spread the fire over 194,000 acres of the Tonto National Forest. Each of the last three years has seen fires of more than 100,000 acres in southern Arizona. Twenty-five percent of the Tonto’s share of the Sonoran Desert now has burned, Lata estimates, and she expects more to burn in years to come.
The Sonoran Desert ecosystem is “only” about 10,000 years old, meaning it’s inherently unstable, Lata adds, with a blend of species still sorting out hierarchy and patterns. Some are adapted to live with fire. Others aren’t.
“When you have that kind of a mix, it’s easy, ecologically, for it to get pushed one way or another,” Lata says. Humans are nudging the entire system to favor species that can survive fire, such as sugar sumac (Rhus ovata), mesquite (Prosopis velutina) and varieties of acacia that have taproots extending several feet underground.
Saguaros and other cacti, in contrast, are among the species on the losing end. Most grow fine roots just below the surface, where they can be easily scorched by fire. The saguaros that don’t die immediately—by exploding into flames—usually die in the following years, their fire-scarred trunks vulnerable to infection or due to starvation because they cannot photosynthesize through their fire-burned skins.
Wildlife dependency on the Saguara summarized by the National Park Service:
Saguaro cacti are host to a great variety of animals. The gilded flicker and Gila woodpecker excavate nest cavities inside the saguaro's pulpy flesh. When a woodpecker abandons a cavity, elf owls, screech owls, purple martins, finches and sparrows may move in.
Large birds, like the Harris's and red-tailed hawks, also use the saguaro for nesting and hunting platforms. Their stick nests are constructed among the arms of a large saguaro. In turn, ravens and great horned owls may take over an abandoned hawk nest.
Saguaro cacti also provide a valuable source of food for animals. In early summer saguaro flowers provide nectar and pollen for bats that in turn pollinate the flowers. The Mexican Long-tongued and the Lesser Long-nosed bats are the two species that pollinate the saguaro at Saguaro National Park. In mid-summer, ripening fruit provides moisture and an energy-rich food for birds, bats, mammals, reptiles and insects during a time of scarcity.
In drier areas of the SonoranDesert, pack rats, jackrabbits, mule deer and bighorn sheep will also eat the young saguaro's flesh when other water sources are not available.