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Saguaro National Park biologist Don Swann looks at saguaro blooms in the Sonoran Desert on Thursday, June 3. Swann takes pictures of 55 saguaros six days a week for the “Saguaro Flower Project.” The cacti are exhibiting irregular ‘‘side blooms’’ this year.

Nestled within the Tucson Mountain District, Saguaro National Park’s main attraction has been exhibiting a strange phenomenon of “side blooms” well beyond their peak blooming season. The flowering event, which occurs from mid-April to early June, has exhibited more buds dispersed along saguaros’ trunks, with smaller flowers and fruits.

The blooms, which serve as a “little oasis” for insects and bats, have been increasing their flowering, leading to increased visitation and pollination according to Benjamin Wilder, director of the University of Arizona’s Desert Lab on Tumamoc Hill.  

“Last August, many of the saguaros got tricked into flowering again, many of those flower buds aborted, they just terminated, the black tissue stayed on the cactus for a month,” Wilder said.

This irregularity can be seen both in and out of Tucson. 

The saguaros, a Sonoran Desert icon, exist along the southern corridor of the Arizona-California border, western Arizona and western Sonora, Mexico. Although they are the most studied desert plant in the world to ecologists, biologists and botanists, these side blooms have caught the eye of local residents.  

Theresa Crimmins, director of the USA National Phenology Network and professor at the UA’s School of Natural Resources and the Environment, stated that desert plants are cued to moisture availability, meaning these plants are well adapted to the environmental variability of dryness. 

Phenology is the study of seasonal events in plants and animals. The local phenology program, in collaboration with USA-NPN’s Nature’s Notebook project put on by citizen scientists, has found random saguaro blooms throughout the year. While the saguaro may be an “opportunistic plant,” these side blooms are not necessarily anomalous.

Researchers at Saguaro National Park, which is home to more than 21,000 saguaros, has been tracking irregularities such as these side blooms for the past year. The Saguaro Flower Project, which began back in 2017, targets a specific plot of 55 saguaros just outside of the Red Hills West Visitor’s Center. Park biologist Don Swann and biological science technician Drew Jackson picked this plot due to its diverse saguaro population, offering them an opportunity to track the different life stages by meticulously taking photographs of each individual cactus in order to track flower and fruit blooms, wildlife interference and environmental changes. 

“The rain we get, the weather we’re seeing, the climate we’re seeing affects how these plants are flowering and maybe we’ll figure out [that] there’s something to this ‘side bloom’ based on precipitation [or] temperatures,” Jackson said.

Generally speaking, blooming or flowering occurs on the “crown” (or top) of the cactus, where new tissue growth has occurred. These side blooms may signify a lack of growth, suggesting that old tissue has simply been reactivated, allowing the cacti to slough off what was supposed to bloom and grow last year.  

This year in particular, many more side blooms have occurred, according to photo evidence of Swann and Jackson’s project.  While some columnar cacti such as organ pipes, silver torches or cardones are known to have side blooms, this recent widespread occurrence is unusual for the saguaro cacti and may be related to environmental conditions that haven’t been fully understood yet, according to Swann. One of the working theories points to last year’s record-breaking drought, with only 4.17 inches of rainfall, according to Tucson International Airport.  A weak monsoon led to a stunted growth of new tissue and spines on the saguaros, “cooking” the newer ones.

According to the National Weather Service, 2020 was the second driest monsoon ever recorded, with only 1.62 inches of rain. A normal monsoon sees 5.69 inches of rain. The year’s extreme heat and dryness may have led to some changes in saguaro flowering. Though Swann says side blooms have been seen before in the park, he’s never seen them at this scale. 

“The challenge for us ecologists is to try and separate the natural cycle of changes from the long-term trends,” Swann said. 

Saguaros are naturally resistant to the droughts which inevitably occur in the desert climate, but some fear that these extreme conditions may continue or worsen, bringing on other changes to the saguaro population. Swann is worried about the future of young saguaros, which only establish themselves episodically.  

“We’ve been in a period now of more than 25 years where we’ve had very low survival of young saguaros in the park,” Swann said.  

The park experienced a growth “surge” in the saguaro population from the ’70s to the mid-’90s, with young saguaros surviving similar extreme conditions. Although this particular saguaro population is reaching a reproductive age, if these present-day conditions continue, there might be a decline in the overall population. 

According to the World Meteorological Organization’s oceanic and atmospheric indicators, this past May closed out the 2020-2021 La Niña event, which may have explained the warmer and drier climate conditions. The lack of rain this past spring was very predictable, suggesting more neutral conditions in the coming months.  

“This is abnormal but not unprecedented,” Wilder said. “It’s very important that we are attentive but not necessarily alarmed. They are very long-lived individuals and we need to listen to what they are telling us and what we’ve observed.”

While Saguaro National Park works towards the conservation of this plant through education on water usage and volunteer efforts such as “Save the Saguaros,” in order to reduce invasive grass species, lessons can be learned by the Tohono O’odham people, who have preserved their symbiotic relationship with the saguaros for thousands of years, maintaining centuries of practice of “subsistence, religion and reaffirmation of their relationship with their traditional environment,” according to the National Park Services. 

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