Arizona’s saguaro cacti, a symbol of the U.S. West, are leaning, losing arms and in some cases falling over as record-breaking extreme heat consumes the state, plant researchers say.
Summer monsoon rains the cacti rely on have yet to come, testing the desert plants’ ability to survive in the wild as well as in cities after temperatures soared above 110 degrees Fahrenheit in Phoenix, Tania Hernandez, a succulents cactus scientist at Phoenix’s Desert Botanical Garden, told Reuters. Phoenix’s Desert Botanical Garden, which covers an area of 140 acres, has over two-thirds of all cactus species, including saguaros which can grow to over 40 feet tall.
“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.
Plant physiologists at the Phoenix garden are studying how much heat cacti can take. Until recently, it was assumed that the plants could adapt to high temperatures and sustain themselves in a drought. However, Arizona’s heat wave is testing those assumptions.
“What’s happening is that the really large old, majestic plants are the ones that are being impacted the most by intense heat waves and droughts,” Kevin Hultine, Director of Research at Phoenix’s Desert Botanical Garden, told USA TODAY.
“A lot of these are aged plants, probably between 40 and 80 years old, are just collapsing because of the combination of drought and heat.”
Hultine explained that saguaros are succulent plants and take up a lot of water, which makes their tissues turgid, allowing them to stand tall and firm. When they don’t get enough water and are exposed to heat and high temperatures, the water-filled molecules in the saguaro’s skin start to drain. As a result, the plant loses structure and begins to shrivel.
“The largest ones in particular will just collapse on themselves,” said Hultine. “The older ones are at more risk of wilting and dying. And part of that is that they just have so much mass to support that they’re the ones that are most susceptible to lose when they don’t get enough water.”
Besides the record-breaking heat, wildfires in Arizona have also posed a major threat to these majestic plants.
“These are plants that are not at all adapted to fire. So we see a lot of mortality in response to fire,” said Hultine.
And fires have been happening more frequently, thanks to hotter temperatures and invasive grasses, Hultine said. The grasses are mostly coming from Africa, he continued and were likely introduced by humans for cattle grazing.
More:All the records Arizona’s heat has broken this month; this week’s forecast
“Sentinel of the Southwest” cacti need to cool down at night or through rain and mist. Long periods of high temperature can weaken and eventually kill saguaros by damaging them internally.
According to the National Park Service, the average life span of a saguaro is 150–175 years, though some plants may live more than 200 years. Hultine says it is “very rare” for the plants to live to 200 and that 150 years “is sort of the typical maximum age”.
Caring for saguaros
If you have a saguaro in your yard, the Desert Botanical Garden recommends giving them supplemental water during periods of drought to ensure that they survive the hot summers.
“The best way to water your saguaro is to make a tree well around the base of the plant and run a hose with a trickle of water for 4-6 hours. This will allow the water to reach deep into the soil (2-3 feet) where the bulk of the roots are,” the garden’s experts recommend. Doing this process once a month during peak summer will be enough to help the plant stay hydrated until it rains, the center says.
However, it warns against overwatering because if water is left sitting around the base of the cactus, it can cause it to fall down.
Heat in the Southwest
July was recorded as Arizona’s hottest month ever, with temperatures over 110 degrees every day of the month, except Monday, the last day of the month. While things appear to be cooling down with lower temperatures on the horizon, it does not mean an immediate end to summer is in sight.
The National Weather Service continues to issue excessive heat warnings in the area, advising people to stay indoors and avoid the outdoors as much as possible.
