For thousands of years, a plant has served as a sentinel in the Sonoran Desert. The spiny giants endemic to Mexico and Arizona, which have thrived through three distinct biomes and migrated north from Mexico over millions of years, are perhaps the region’s most distinctive feature.
But for more than two decades, little new saguaro sprouts from the desert soil.
Researchers at the University of Arizona Desert Research Institute in Tumamook Hill don’t know why.
delicate process
Frank Reichenbacher, a botanist and volunteer researcher at the institute, says the saguaros are missing out on breeding opportunities as the summer monsoon comes earlier each year.
“The seeds are designed to germinate in the monsoon rains that fall shortly after the seeds are dispersed,” he says. “So the flowers bloom in April, the fruits ripen in May or June, and then the fruits either drop seeds or animals pick them soon after. Then the monsoon hits.”
Shorter time to summer monsoon means less time for seeds to germinate and less regeneration. Seeds that develop after the first monsoon hits receive less water and are less likely to regrow. And as the monsoon approaches hastened, the saguaro blossoms cannot be adjusted.
Desert Research Institute staff researcher Peter Breslin said it was unclear what metrics the Saguaro used to adjust its timing. What is clear is that how prolific flowering is depends on winter rains, which have steadily declined over the past few decades.
“Rainfall has changed, but to no avail,” said Bill Peachey, an independent ecologist and botanist based near Tucson.
Peachey said the 2022 winter’s low rainfall meant that few saguaros bloomed last spring. Saguaro has had a successful flowering event only 12 times in the last 20 years. A plot of 139 saguaro trees on state land in Pima County, 45 miles southeast of the Desert Research Institute in the Tumamok Hills, about 1,000 feet high, counted 120 flowering in 2004, but not in 2022. Only 50 bloomed.
“Nothing came of fruit,” he said.
Peachy said these low flowering events coincided with extreme heat. Saguaro blooms at this time were even scarcer than in the 2011 freeze period and his two years thereafter.
“You can’t say this is climate change,” he says. “These are weather events. But these weather events are exactly 100% in line with his two key statements on climate change: we will have more weather events than before, and we will have extremes. climate change will occur.”
Some of the saguaro on site didn’t survive the 2011 freeze, but Breslin said temperatures could be slightly warmer at lower elevations, so Tumamok Hill isn’t showing any lasting signs. . In the Santa Catalina Mountains, the saguaro “bloomed like crazy” last year, but elsewhere it was virtually dormant.
“They are as dynamic as daisies,” Peachy said of the saguaro’s diversity due to different temperatures and topography. “Things change, they change.”
The Mystery of Wakisaki
One of the most significant changes in saguaro behavior was the side bloom in 2021.
“We’ve never seen anything like that before,” Reichenbacher said.
Flowers are sprouting from all sides of the cactus, rather than just the stems and arm tips of the saguaro, in what the National Park Service calls an “extremely rare phenomenon.” In fact, it’s so rare that no one knows why it happened.
Side blooms themselves are not uncommon. Even if the Saguaro Areole doesn’t sprout in the spring, it can still flower the following year. Being lower than the spine and unable to get enough sap to sustain the flower, the flower is quickly aborted and falls off. But even in 2021, not everyone has had an abortion. Many of them have come to fruition.
“It’s disconcerting,” said Peachey, who was one of the first to notice the strange pattern of flowering. “In my experience that is not the case.”
A small hole along the saguaro’s ribs is called the spinal cord. Each isole sprouts clusters of spines and stem cell tissue that become either flowers or arms. Tubules travel from the center of the cactus, called the cortex, through the xylem ribs to the latest spinal arenas, carrying nutrients and signals from the stem.
Peachy explained that tubules are pinched from the areore, usually after the areore blooms, as the ribs grow larger from the bottom to the top.
But not all tubules are picked at once. If the areole has not flowered and the rib has not yet been detached from the tubule, it may bloom again later in the year when it is further down thanks to a new aorere that has grown on top of it. This is uncommon as both events need to be synchronized. The flowers that form on the sides of the saguaro are usually discontinued quickly because cacti cannot support the lateral flowers as well as they can support the tip flowers.
Neither Peachey nor other scientists have a definitive explanation as to why flowering has not stopped, and there is nothing to compare it to in the past.
Since 2020 was the hottest and second driest year in Arizona’s history, observers hypothesized that the unusual bloom in 2021 might have been a stress response. But National Park Service researchers have a different idea. hypothesis.
Saguaro productivity is strongly influenced by April soil moisture levels accumulated by winter rains. April 2021 was particularly dry, but April 2020 and he April 2019 were wet enough to maintain average vegetation conditions. So researchers at the National Park Service hypothesize that the past few years have already set the stage for a large-scale seed production called a “fattening event.” Whether large-scale seed production results in regeneration will depend on wet conditions over the next few years.
But Peachey points out that in the last 20 years, eight of the last 20 springs have had very few flowers. The fewer areores that flower, the more will remain active the following year. This means that later in the year more will bloom on the sides and cease before flower formation.
“But it’s kind of depressing because two years ago it wasn’t like that at all,” he said. “They worked perfectly, all the way down.”
It’s still early in the flowering season, but some saguaros in the northern Sonoran seem to be starting to sprout from the sides, but it’s unclear if they’ll bloom as expected, or if they’ll bear like they did two years ago. His one of the cacti in Tumamok Hill sprouted slightly from the sides in mid-April, but the sprouts looked mostly normal, Breslin said. None of the 79 saguaros that bloomed on the site Peachey studied had side blooms.
naturally failed
Even if the weather were all right, the chances of the seeds germinating would still be very low. Some saguaros can live up to 250 years and leave no offspring.
“If you took literally a million saguaro seeds and just threw them away, in five years there would be no seeds at all,” says Breslin.
In a lifetime of about 175 years, the saguaro will release between 11 and 39 million seeds, Peachy said, giving rise to just one more saguaro. Each fruit he contains 1,000 to 6,000 seeds.
So why is it so difficult for seeds to survive?
“People don’t really know,” says Breslin. “There are some traits that we know of. Small seedlings are probably easier to eat than other plants.”
Saguaro seeds are only a few millimeters long and contain a lot of water.
“Because water is water, it’s very attractive to pack rats and other animals,” he says.
The saguaro seed has sprouted but is not yet out of the forest. The seedling is very sensitive to frost in his first decade of life, and the smaller the seedling, the more sensitive it is to heat and drought. If a seedling grows twice as big, it can live 10 times longer without water, but it’s hard to grow that much.
Breslin hopes to find more answers by reviewing the results of a study conducted last year on more than 4,000 of the roughly 12,000 saguaro birds in the Tumamoc Hills. He and other researchers recorded the cacti in each of four sections of the hill, recording data on height, number of arms, and signs of damage or problems.
They also looked at microsite features, such as areas covered by rocks and vegetation, and the presence of invasive buffergrass and slopes. A microsite is her square meter site where the saguaro grows, measured by the elevation change of the site.
Saguaro establishes different terrains. Some prefer sandy soils, while others grow on rocky terrain. In some cases, only north-facing is installed, in other cases, only south-facing is installed. Smaller saguaros prefer more vegetation and rock cover as it helps regulate temperature and prevent cacti from being eaten.
Breslin hopes that his research will help us better understand this variability and predict how climate change will affect us over the next few hundred years. He hopes to publish the first paper of his findings by September.
“Our results may help us understand how best to restore cactus populations in the environments people prefer most,” Breslin said.
Breslin acknowledges the limited data available. Saguaro’s first expedition in the Tumamoc Hills was his in 1964, and expeditions have been conducted every ten years since. However, 60 years is still short-term data and can be misleading.
“A lot of people at 60 still don’t have arms or flowers,” he says.
Breslin said this year’s flowering, which began in Tumamok Hill in mid-April, should be “average to good” next month based on current bud formation. Peachy said about 50% of the saguaros on the plots surveyed have flowered and are already doing much better this year than last year.
“[But]sometimes big flowers do not regenerate,” Breslin added.
The future may look bleak for Saguaro. With an aging population in the Tumamoc Hills and few new saguaros, Breslin said there could be major fatalities in the next 60 years or sooner. If something doesn’t change, the effects could spread throughout the Sonoran Desert.
However, not all saguaros are going extinct. Peachy is convinced that life will always work out.
“The saguaro will go extinct because the saguaro will die where it used to live,” he predicts. “Hundreds of years from now, whatever we do,[nature]will decide where we want the temperature to be and we’ll be back to normal.
“When they start showing up again, it’s going to be magical.”
