Arizona saguaros are collapsing in this extreme heat, and experts are worried

PHOENIX - The saguaros that tower over the Sonoran Desert are synonymous with Arizona and are known for their resilience, but experts are concerned that this heat could be too much for them.

The cacti usually live about 150 years, and inside their skin, they can reach up to 140 degrees inside. Still, the prolonged dryness and intense heat could be a problem.

"Saguaros, like a lot of cactus, are pretty remarkable for their tolerance to warm conditions," said Kevin Hultine, director of research with the Desert Botanical Garden. But when you start seeing prolonged temperatures like that, the long term impact can be pretty profound."

He says the skin tissues of the cactus play a big role in its growth and health.

"When it gets dry, those tissues start to get really soft and these large plants, the really majestic ones in particular, will literally collapse on themselves, so that’s one of the big concerns we have," Hultine said.

It's happening under extreme and prolonged heat conditions, with little to no moisture.

"We know in 2020, the extended heat wave we had then had a major impact on saguaros, we saw higher rates of mortality, and will probably see higher rates of mortality in the future just based on what happened in 2020," Hultine explained. "So when you add this major heat wave in July, it’s possible that this will compound that."

There's still several weeks of summer left to go, and more monsoonal moisture could help out - not just with living saguaros, but with their seeds.

"So these seeds are in the sun, and it's hotter than ever and they're cooking and dying, so that's the real issue here," said Frank Reichenbacher, associate researcher at the University of Arizona's Desert Laboratory. "The vast majority, 99%, maybe a lot more than 99% die in the sun."

And as those seeds dry up, so do the cacti. They're losing arms or collapsing entirely.

"Saguaro seeds are poorly nourished. They don't last long in the ground and they're timed so that they're released into the environment just before the monsoon hits," Reichenbacher said. They're waiting for the monsoon."

Long-term impacts to a species that can live for decades, says Reichenbacher, are still unknown.

"We're not sure if this drought that we're in is a new normal or if it's just a blimp in the climate and it'll be over soon and things will be back to normal," Reichenbacher said. "If that's the case, then we would expect the situation to be more in favor of saguaros."

But for now, just on Tumamoc Hill, the research team from the University of Arizona says the situation is not looking up.

"A total of 4,000 plus saguaros on Tumamoc Hill in four different plots, he only found about 30 new ones," Reichenbacher said. "That's not enough."

The warm nights, say scientists, are also ruining the cacti's photosynthesis process, which also costs it even more water. 

Experts believe we still might not know the full impact on this heat wave to these plants for several months or even years.