Saguaros, especially older ones, have died as a result of a brutal freeze last February - and researchers say the cold had a "horrific" effect on last year's saguaro bloom.
"We've seen an increase in the deaths of large, older saguaros at the park in the past year as compared to previous years," said Don Swann, a biologist at Saguaro National Park.
"Many of the middle-aged saguaros seemed to show little or no effect" from prolonged freezing weather in early February, Swann said. "Some of the smaller ones seem to have done fine, but there was some damage to other smaller saguaros - especially at higher elevations."
Last year started with extreme cold in the Tucson area, down to 21 degrees on Jan 1. A month later, the Tucson area had 18-degree readings on Feb. 3 and Feb. 4.
Swann said he couldn't estimate the number of saguaros that fell victim to the freeze until follow-up studies can be done. And he emphasized that it's not possible to say for certain whether a particular saguaro died from the freeze - or whether the death stemmed from other causes, or a combination.
By no means is the saguaro population facing a large-scale die-off as a result of the freeze.
Still, the immediate future of many saguaros might be impacted by the cold snap's apparent effect on blooming and fruit production.
Swann noted that "flowering was definitely down last year after the freeze, but it varied in different parts of the park."
He cited the work of Tucson-area geologist and longtime saguaro researcher Bill Peachey, who recorded a drastic drop in saguaro blooms last year.
"I have a detail plot in the Rincon Valley - about 2 1/2 acres in size - where I've been studying saguaro blooming since 1997," Peachey said. "I literally count every flower that's out there.
"It was horrific, what happened after the freeze," he said. "I had five saguaros that just died outright on the plot, ... and then the 2011 bloom was vastly reduced. In 2010, I had 7,009 blooms out there. In 2011, I had 552 blooms."
Peachey said he attributes the sudden decline in the bloom count to the extremely cold weather.
"It must be the freeze. There was no other phenomenon that occurred. Nobody sprayed Agent Orange out there," he said.
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A saguaro census conducted in 2010 estimated that there are 1,896,030 saguaros in Saguaro National Park.
"It was horrific, what happened after the freeze. I had five saguaros that just died outright on the plot ... and then the 2011 bloom was vastly reduced."
Bill Peachey, longtime saguaro researcher
Contact reporter Doug Kreutz at email@example.com or at 573-4192.