Walking Among 2,000-Year-Old Plants in the Mojave

On Thursday a couple of friends who have been trying to pry me away from my computer for weeks actually succeeded. We got in their truck and went here, more or less, to a place I'd been wanting to see for some time -- a spot where there are huge rings of Mojave yucca.

Mojave yuccas, scientifically known as Yucca schidigera, are one of the most common plants in the California desert. Desert travelers can recognize them readily: they look vaguely like Joshua trees, but are far coarser and more robust in structure, with heavier trunks and thicker leaves. As often as not you'll see Mojave yuccas growing in clumps. Sometimes those clumps have empty space in the center. Because each individual stem in such an open-centered clump is a genetic duplicate of its colleagues, botanists refer to such groups as "clonal rings."

Once you know they're there, you start seeing clumps and rings of Mojave yucca everywhere in the desert. They're as common as liveoaks on the California coast. And most people seeing them don't realize that even the smaller clumps can be mind-bendingly ancient.

Making even a small clump of Mojave yucca takes a long time. The plants grow very slowly. From the time a Mojave yucca germinates it grows less than an inch in height each year in ideal conditions, where temperatures are relatively moderate and winter rains predictable. In places where the desert is especially hot and dry, that growth slows to a painstaking crawl, a quarter inch a year or so. In that kind of setting a yucca stem can take two centuries to grow four feet tall.

Plants are mature enough to flower and set seed after about 35 years. A century after that, a typical Mojave yucca starts reproducing without flowers and seeds: a bud at the base of its trunk will grow into a rosette of leaves. As year after year passes that rosette will grow a trunk of its own, a centimeter at a time.

Fast forward your observations of this new pair of yucca stems so that each year is a still frame in a centuries-long film. 250 frames in, each of the two stems has produced a new side shoot, making four stems in the clump. At frame 375, that's eight stems; at frame 500, it's 16. Eventually the first two stems in the center die back after centuries of competing for water and nutrients with their offspring. The clump has a donut hole. Older stems lining the hole continue to die off as new stems are produced on the outside of the clump, now a ring.

Show that film all at once: a yucca seed hits the ground, and an impossibly slow ripple expands outward across a sea of desert.

The times I mention above are approximations, and yuccas grow faster in some places than they do in others. Still, the following rule of thumb is a conservative enough guide to estimating the age of a yucca ring, as long as you aren't working on a peer-reviewed paper: for every foot of a yucca clonal ring's diameter, figure a century of age. A 10-foot ring, not at all hard to find in the desert, would thus ballpark at a thousand years old.

In 1983, the Bureau of Land Management fenced off about 5 acres of the Johnson Valley off-road area, designating it the Upper Johnson Valley Yucca Rings Area of Critical Environmental Concern (ACEC). We parked outside the fence and walked in, spent some time with our elders. One of the rings, easily visible from the road, was a good 20 feet across. A sign on the BLM's fence did the math, saying that rings within the fence could be 2,000 years old.

There were relative youngsters inside the fence as well, a mere 700 or 900 years old, some of them still without their donut holes. Other plants in the enclosure were no slouches in the longevity department either: the mineral soil had sprouted creosotes and pencil cholla many of which were at least centuries old.

As the three of us walked the enclosure, we noticed that the hills beyond and to our south, an arm of the Fry Mountains, held yucca rings that appeared larger and more numerous than those in the fenced-off ACEC. We left the fenced area and walked a ways into the Frys, following what might have been an old footpath or someone's dirtbike track from 1973. There were plenty of yuccas there, all right, along with blooming chinchweed and scattered clumps of cottontop cactus, which themselves were at least decades old:

I took a number of photos, including the one below. I didn't realize what I had until I got home.

I need to head back with a tape measure, which will have to wait until I have access to a four-wheel-drive vehicle. But I can't shake the thought that this ring looks to be at least 25 feet across, maybe 30.

Which would mean this plant had germinated before Carthage was destroyed, and possibly before Carthage was even founded. Or use your own yardstick. It's about as old as the General Sherman tree. Older than the oldest known coast redwood. Older than Christianity; older than Alexander the Great. This yucca might have germinated as Sophocles wrote "Oedipus the King," as Buddha sat unrecognized beneath his bo tree, as the Olmec ruled in Mexico.

And that's not even particularly remarkable for the neighborhood. A short distance to the east a 67-foot ring of creosote, which built itself in a fashion not dissimilar to the yucca rings' origin, has been estimated at 11,700 years old. If the yucca ring in the photo is as old as I think it might be, King Clone the creosote ring was already pushing 9,000 years old when the yucca first germinated.

To walk out into the desert is to walk among the ancients, beings to whom our short lives are mere flashes against a long and patient backdrop.

Unless, of course, we misbehave, as for example in this clip from a couple years back of contractors clearing a patch of desert for a solar facility:

Of course that yucca was a relative youngster, probably not more than 800 years old.