Cacti thrive in the shadows of catastrophes

Even giants need a helping hand as children, but for saguaro cacti that hand comes from a long way away.

It looks like there’s going to be an excellent talk at the ESA Meeting in Florida this year. One of the speakers, Taly Drezner has put out a press release on cactus growth. She’s noticed a number of cacti that seem to date from 1884.

Saguaro cactus
Biogeographer Taly Drezner stands beside a middle-aged saguaro cactus at Kofa National Wildlife Refuge near Yuma, Arizona. Credit, Taly Drezner

The saguaro cacti, Carnegiea gigantea are the tallest plants in many parts of the Sonoran Desert. Yet, while they’re sturdy as mature plants, as younglings they’re vulnerable. A small plant can easily dry out or chill in the desert. When something happens that can turn the climate in their favour then they have a much better chance of survival. And they need a much better chance of survival. Conditions in the Sonoran desert are so harsh that nearly all young plants die in their first few years.

So what happened in 1884? Not a lot. But 1883 was a major year for the climate.

1883 saw the eruption of Krakatoa, west of Java. Tens of thousands of people perished due to the eruption, and the effects were felt worldwide. One idea is that the red sky of Munch’s The Scream is a representation of the red skies around Norway after the Krakatoa eruption. Aerosols high in the atmosphere chilled the Northern Hemisphere by over a degree centigrade (and over 2 degrees Fahrenheit).

The volcano certainly made it’s demise felt in California. July 1883 to June 1884 had record rainfall. The water and the protection from the heat of the summer seem to have been excellent conditions for saguaros.

“I started noticing that these saguaro age cohorts followed notable volcanic eruptions,” said Drezner. “I knew that volcanoes drive milder summers and winters, and typically more rainfall for an extended period–two to three years after the event, which is a perfect window of time for the saguaro to get established and have a chance to survive.”

Co-incidence? Drezner has been testing her idea by getting cacti dates from Kofa National Wildlife Refuge near Yuma, Arizona. The Kofa National Wildlife Refuge is an excellent place to test the hypothesis as it’s a tough environment. It gets just a third of the rain the Sonoran Desert gets elsewhere.

It’s not just Krakatoa that correlated with a saguaro boom. She’s also found connections to Mt. Pelée, Soufriere, Santa Maria (1902), Ksudach (1907) and Katmai (1912). That has consequences for cactus conservation.

“The saguaro are protected because they are a beloved symbol and icon of the desert,” Drezner said. They are not currently threatened, but the unpredictable nature of their reproduction makes some conservators nervous about how the giants will respond to a changing climate. “That a volcano elsewhere on the continent, or even the other side of the world, can so profoundly influence a local population underscores interconnectedness of ecosystems and our global climate.”

You can catch the talk on Tuesday, August 9 at the staggeringly early time of 8:10 AM.