Climate Change Threatens Saguaro National Park’s Cacti
By Lis Cohen
Looking out over Saguaro National Park, which brackets Tucson, Ariz., like a pair of oversized parentheses, it’s hard to imagine how anything survives in this parched, sandy, sun-baked landscape. Millions of years of evolution have created an ecosystem here, though, with Gila monsters, kangaroo rats, snakes and other tough, scrappy creatures. The plants are equally tough — and towering over them all is the massive Saguaro, the park’s namesake and the species everyone thinks of reflexively when they hear the word “cactus.” Saguaros are a familiar fixture in everything from Road Runner cartoons to Clint Eastwood spaghetti westerns; with their upward-reaching arms, these slow-growing plants, which can grow up to 60-feet high, look like over-eager students desperate to be called on by their teacher.
Founded in 1933 as a National Monument, and elevated to park status in 1994, the park is meant to be a protective haven for these majestic desert plants. But park managers are increasingly worried that climate change could destroy them. National Parks across the U.S. are wrestling to varying degrees with the changes coming as the planet warms. Nowhere, however, do park officials take it more seriously that they do here.
Scott Stonum is the park’s Chief of Science and Resource Management and Andy Fisher, the Branch Chief of Interpretation (in plain English, she’s the one in charge of explaining things to visitors). It isn’t just the changes in climate he’s concerned about. “Our main issue,” Stonum said, “is resilience.”
ON THE FRONT LINES
Saguaro National Park: Volunteers battle an ever-dominating invasive species
Antonio Busalacchi: Climate Scientist and Certified Specialist of Spirits
Keith London: City commissioner, Hallandale Beach, Fla.
Katharine Hayhoe: Climate scientist and professor at Texas Tech University
Abigail Borah: 21-year-old Middlebury College junior
Edward Lu: Astrophysicist and electrical engineer
Michael Mann: Climatologist and physicist
A healthy, flourishing ecosystem, even one in such a barren place as the desert of southern Arizona, is a lot better able to withstand climate change than an unhealthy one — and the ecosystem here is not healthy. It’s under assault by an invasive species known as buffelgrass.
Native to Africa, buffelgrass was imported to Arizona for cattle forage and erosion control in the 1940s. Like many such imports, which seemed like a good idea at the time, this one has gone out of control (the classic example is kudzu, which is in the process of swallowing the Southeast). Approximately 2,000 acres of the park are currently covered with buffelgrass, and can spreading at a rate up to 35 percent per year. It has the potential, Stonum said, to turn the expanses of Saguaro-dominated landscape into grassland.
“What it [buffelgrass] does,” Stonum said, “is out-compete the native grasses, the native plants, and the cactus, and it literally excludes all the new plants.” This is a problem for creatures like the desert tortoise that feeds on native plants. Young tortoises may be somewhat protected from predators by the buffelgrass, but by the time tortoises are big enough to reproduce, the decrease in native plants can make it harder for the tortoises to do so. This reduces the tortoise population overall.
Compounding the problem, he explained, is that buffelgrass thrives on fire. The Sonoran desert ecosystem where the park lies is dotted with vegetation, but with significant gaps where there’s nothing keep a fire going. Fires may start — Tucson is a lightning hot spot in the U.S. — but the gaps keep them from burning out of control. Where the buffelgrass fills in, fire can spread more easily and burn hotter. The roots of the grass survive, so it grows back easily.
Saguaros, which are lucky to generate a single mature offspring from tens of millions of seeds, can’t. “They melt and die,” said Stonum.
This is a problem not just for the Saguaros, but for the creatures that depend on them. For the animals that live in them, such as gila woodpeckers and glided flickers, Saguaros are like luxury hotels, with heating, cooling, and breakfast included. These birds peck out little caves in the cacti — the woodpeckers preferring rooms on the lower floors, while the flickers opt for the penthouse — that stay cooler in summer and warmer in winter, by about 20°F in both cases compared with the temperatures outside. Once the woodpeckers leave their nests, animals like cactus wrens, elf owls, mice, snakes and spiders move in. The fruit and seeds of the cacti, meanwhile, provide food for creatures as diverse as coyotes and cactus wrens.
A young saguaro cactus surrounded by buffelgrass. Credit: National Park Service.
Worrisome as the increased danger from fire is, the Saguaro and other park species are threatened by changing weather patterns as well. Currently, the region’s bone-dry conditions are interrupted by two intensely rainy seasons: one in winter and one in summer. “This is really advantageous to the cacti,” Fisher said. “They’ve adapted to have their flower season, their fruit season, and their seeds timed just perfectly to the monsoon rains.” Climate modeling studies by Jeremy Weiss, at the University of Arizona, project that in the next century, southern Arizona’s climate could see a 10 percent decline in precipitation. You can get more information about climate change in the region by going to the Southwest Climate Change Network.
Projections also show that summertime high temperatures in the southwest will rise by 7°F on average. Animals are likely to react by trying to move to higher altitudes, where it’s cooler, but species that already live at high elevations, including the Mexican Spotted Owl and the black bear, are mountain dwellers that have nowhere to go.
Species that inhabit the lowlands, meanwhile, will move uphill, disrupting the park’s ecosystem even further.
And that in turn will disrupt the visitor experience, to the point where people who come to Saguaro National Park may no longer have any Saguaros to look at. To raise awareness about the problem, Fisher and her team are working messages about climate change and invasive species into the park newsletter and into visitor talks. “Resiliency is a main topic,” she said. “We weave it into everything that we do because it is such a large part of who we are.”
After four years of effort, one area of the park known as the Freeman Homestead has finally been declared under control. Credit: National Park Service.
Fisher said the response from visitors has been extremely supportive. There’s no way for one park or its visitors to hold back global warming, but while park employees attack the fire-loving buffelgrass with herbicides, volunteers show up once a month for communal buffelgrass pulls. There’s also a Weed Free Trail volunteer program for those who want to do more. It’s a difficult battle, but after four years of effort and thousands upon thousands of buffelgrass clumps yanked from the ground, mostly by volunteers, one area known as the Freeman Homestead patch has finally been declared under control.
It’s just a small victory, of course, but if Saguaro National Park staff and volunteers are successful in their fight against buffelgrass, they may at least be able to save Saguaro from a fate that’s almost certain to befall another park a thousand miles to the north. It’s quite possible that by the end of the century, or not long thereafter, Glacier National Park, on the U.S.-Canadian border, may no longer boast any glaciers. With enough effort, Saguaro National Park may be able to hold on to its Saguaros for at least a bit longer than that.
Lis Cohen is an intern at Climate Central and a graduate student at the Woodrow Wilson School of Public & International Affairs at Princeton University.