Protecting our spiny friends
Saving the West’s most iconic cactus from climate change
TUCSON » The giant saguaro, an icon of the American West, is beloved in this state. Arms raised in a perpetual “hello there,” the saguaro covers the desert wilderness and thrives in cities. Its silhouette appears in fine art and on restaurant walls; businesses and schools carry its name. Arizona state law protects the plant, and it is revered by the native Tohono O’odham tribe.
The largest cactus in the United States, the saguaro is distinct, visually and biologically. A mature saguaro can grow to 40 feet and weigh a ton after soaking up rainwater. Supported by its wood skeleton, the saguaro can sprout dozens of arms. Sometimes the arms are curled; if two are growing side by side, they’re often hugging.
The saguaro grows in just one part of the world: in the Sonoran Desert of Arizona; northern Mexico; a smidgen of California; and most prolifically in a mountainous swath that flows west from Tucson to the California border. It’s a landscape of rock, hard sand and open blue sky, and the saguaro has been part of it for 10,000 years.
And now, a changing climate is raising concerns about how the saguaro will survive the 21st century in an environment that’s hot and getting hotter, dry and getting drier. In a climate wake-up call, drought and record-breaking heat in 2020 contributed to wildfires that killed thousands of saguaros.
But the saguaro has friends keeping watch. There is a special affinity between the saguaro and science, a linkage that has made it one of the most studied plants in the world.
“If we’re going to find any communities or ecosystems well suited to these climate stressors, the desert is going to be a pretty good one,” said Benjamin T. Wilder, director of the University of Arizona’s Desert Laboratory on Tumamoc Hill, where botanists began studying the saguaro 118 years ago. “I wouldn’t bet against a desert species.”
The summer of 2020 “fits with what we are going to continue to see with climate change,” says Wilder, beginning with the monsoon.
North America’s only monsoon - and the reason the Sonoran Desert is billed as the world’s “wettest desert”brings billowing cumulonimbus clouds that drench the land in rain. Nearly half the annual rainfall required to hydrate the Sonoran Desert is delivered by the monsoon.
Last summer, the monsoon never came. A pitiful 1.62 inches of rain fell, compared with the average 6.08 inches - a rare occurrence that in meteorological dark humor is termed a “nonsoon.” As a result, 2020 was Tucson’s driest year on record, according to the National Weather Service. The lack of rain compounded long-term drought conditions.
Michael A. Crimmins, a meteorologist and University of Arizona Climate Science Extension specialist, suspects that the nonsoon resulted from multiple forces, citing La Niña and El Niño, climate patterns in the Pacific Ocean that affect weather around the globe.
Individual weather events don’t inform a trend, Crimmins said. But 2020 was also Tucson’s hottest summer on record. Over the course of 124 uninterrupted days, daytime temperatures never dropped below 100 degrees, with 50 of those days peaking at 105 degrees or higher.
While heat is not necessarily a threat at this point heat makes the cactus grow - it has contributed to a devastating new risk: fire kindled by invasive buffelgrass, a South African import. Buffelgrass, which has been thriving in hotter, drier conditions, forms a flammable carpet around the cactus.
Thousands of saguaros died on the buffelgrass-laden lower slopes of the Santa Catalina Mountains on the north side of Tucson in June, when a massive lightning-ignited fire erupted and burned for seven weeks.
In response, hundreds of Tucson residents regularly volunteer to hand-pull the grass from city, county, state and national parks. The Arizona-sonora Desert Museum, a 98-acre outdoor zoo and botanical garden, declared February and March “Save our Saguaros” months, encouraging the public to identify and remove clusters of buffelgrass, which it terms a “menace.”
The museum has partnered with the Desert Laboratory on Tumamoc Hill on a 10-year plan to eradicate buffelgrass from an 80-acre site on the hill. Removing buffelgrass is key to saving native cactus as dry conditions intensify. It involves grueling work by hand and garden hoe, and the occasional use of chemicals.
The effects of climate change are being felt in saguaro country. Just how deeply is under study, with a caveat wrapped in a conundrum: How do you fully assess the impact as it emerges today on a species that lives at least twice as long as the researcher?
The intrepid botanists who began research on the curious armed cactus proliferating on Tumamoc Hill created an extensive baseline of data and observations for generations of scientists to come. The work expanded as the U.S. Forest Service and, later, the University of Arizona took over lab operations.
“You’re not going to find longer records in the Southwest than what is up on the Hill,” said Kathryn A. Thomas, a research ecologist with the U.S. Geological Survey. Her work uses models to forecast how the saguaro’s habitat may change as the planet warms.
Broadly speaking, it appears that a suitable climate for the saguaro is “going to be maintained or even improved in a fair number of places,” including the Tucson-to-california corridor,she said.
But those models fail to take into account the impact of the increasingly hotter, drier climate on the plants around the saguaros.
The models do not address the important community of plants - called “nurse plants” - that grow with saguaros and protect and sustain the seedlings. The models are specific to adult saguaros, not to the rejuvenation of the population as a whole, she said.
And they don’t reflect the full impact of invasive species such as buffelgrass.
“The climate might be fine for saguaros, but if they’re being burned up by buffelgrass,” all bets are off, Thomas said.
Saguaro National Park has become an important adjunct to the study of the saguaro. The park, which attracted more than 1 million visitors in 2019, protects 92,000 acres of the cactus in two divisions, on the east and west sides of Tucson, and boasts a vast collection of young and aged specimens.
In one recent study conducted in the east side, Crimmins and National Park Service biologists Don E. Swann and Adam C. Springer examined the assumption that saguaros could do the same as other plants struggling with global warming and expand their range to escape to cooler ground.
Take a closer
look at the stems of your houseplants. Any young, new leaves?
Swelling buds? Inside their pots, roots might likewise be awakening. All of this makes today,
tomorrow, or sometime soon a good
time for repotting and
pruning.
No matter that winter winds and snow still come and go in much of the country. The sun’s earlier rising and higher climb into the sky let us know that spring is on the way. Even houseplants indoors feel the changing season.
Take a closer look at the stems of your houseplants. Any young, new leaves? Swelling buds? Inside their pots, roots might likewise be awakening. All of this makes today, tomorrow, or sometime soon a good time for repotting and pruning.
How tall is too tall?
The most obvious reason to prune a houseplant’s stems is to keep the plant manageable. For example, growing in the ground in a tropical climate, branches of weeping fig, a familiar houseplant, will reach skyward and spread as high and wide as a sugar maple’s. Indoors, at the very least, your ceilings limit the desired height of a houseplant. For looks, you might want to keep the plant smaller, perhaps much, much smaller.
When pruning the stems of a houseplant, the goal is to reduce its size without giving it a hacked-back look. For a plant with many stems, such as a weeping fig, a few severe cuts usually gives better results than many small cuts. Trace one of the tallest stems down to its origin, and cut it off right there. Perhaps do this with another tall stem too.
After one or more drastic cuts have lowered the plant, go back over the plant to make some smaller cuts. Cut back any dead or diseased stems, and any that look gawky or out of place.
There are houseplants, such as dracaena and ponytail palm, that naturally sport only one or very few stems. These rarely need pruning; when they do, it’s because they’ve finally grown too tall. Lop back the stem to lower than the final desired height. New growth will appear near the cut, perhaps even a couple of new stems. If you want to keep the plant single-stemmed, remove all but one of the emerging stems.
Check below ground also
Pruning the stems of a houseplant is just the first step. After a few years, depending on how fast a plant grows, roots will fill a pot until they have no room left to grow. Roots attempting to escape out the drainage hole of a pot is one indication of overcrowding.
More telling is to have a look at the root ball itself. Slide the root ball out of the pot. If it’s a large plant, the easiest way to do this is to first tip the pot on its side. Are the roots cramped together and circling around and around the outside edge of the root ball?
If the roots are overcrowded, you could just move the plant to a larger pot. Of course, then it will grow even bigger, which may or may not be your wish.
If the plant is to go back into its old home, root pruning is needed. Stand the plant upright and — brutal as it might seem — slice off the outer edge of soil and roots all around the root ball. The bigger the root ball, the more you can slice off.
Stand the plant back in its old pot and pack new potting soil in the gaps between the shorn root ball and the container. Use a stick or your fingers to firmly press it in place.
Water the plant, and it’s ready for spring.
Not for every plant
No need to prune and repot every houseplant every year. Many grow very slowly, so might need this treatment only every few years. And some plants — clivia and amaryllis, for example — grow in clumps rather than skyward-shooting stems, and actually do better with their roots cramped in their pots.