Every time I go to Joshua Tree, I see wrinkly cacti on the ground, looking like they’re either all dying or all meant to look that way. And, because most plant guides don’t show this particular cactus in its wrinkly state, I couldn’t quite always figure out which one it was.
I also realized, once I (hopefully) identified it, that this is a perfect candidate for using plants to spot clues about environmental differences. In particular, because I can see this cactus both in Los Angeles and out across the rest of the Mojave (and further, because it grows quite widely), I want to use it to judge how well-watered any particular region is.
The Life of the Prickly Pear Cactus
Prospectors and miners in the desert must’ve never envied this prickly little menace. Growing up to about knee height and wider than it is tall, all the leaves are beaten down by the sun. Surviving in temperatures between the frost of the night and the heat of the Mojave sun, they thrive on mere inches of rain each year.
Cacti are true drought-specialists. Their stems are often ribbed or fluted, allowing them to expand when full of water. Their roots stay close to the surface, where the desert rains barely penetrate. Even more astounding, cacti time their respiration (and potential water loss) through a process known as crassulacean acid metabolism. They breathe at night, limiting their potential water loss. During the day, their pores close up and the plants engage in photosynthesis with the stored carbon dioxide.
Ranging from green to blue-gray to purpling, the Beavertail cactus has thickened stems at largest about the size of a stretched out hand. Like most cacti, they have small spots where painful points protrude. In the case of the Beavertail, these are small barbed bristles called glochids. Trust me, you don’t want these in your skin. These bristles are the leaves of the cactus, and they grow from a reduced branch known as an areole. Not providing any photosynthesis, they instead offer protection and a touch of shade. In the case of this wrinkly cactus, no real help at all – and probably why some look eaten-through.
|(for yr. 2020)||Joshua Tree||Los Angeles|
|Total Rainfall||5.8 in||24.2 in|
|Daily Average||0.02 in||0.1 in|
|Wettest Day||Mar 12, 2.2 in||Mar 22, 4.7 in|
|Num. of Wet Days||9/344||25/344|
The number of days listed reflects that this data was recorded before the full year has passed.
Sources: Here and Here
Let’s start off assuming there’s no wild chemical issues at hand – though with how smog rolls in from the cities to the west, that’s always possible.
There’s a chance that this odd wrinkling is caused by some disease. I haven’t turned up research confirming that yet, so I’m going to skip that too.
That leaves water as the key difference.
In Los Angeles, as part of planters and water-conscious gardens, these cacti are thick and healthy. Often, they’ll have parts that are old and browning, having grown to the end of their normal lifespan. Also, they’ll flower and fruit.
On the other hand, the cacti in Joshua Tree are stunted and often literally shriveling under the sun. It’s much less common for a second or third division of the stem to bring it up to full height.
Looking at the shape of the stems, it seems like pads of this shape will generally just thicken when full of water. In the Joshua Tree cacti, it looks like the plant has run out of water and is trying to reach into itself for more.
LA receives four or five times as much rain as Joshua Tree, on average. There’s more than twice as many days where rain falls, giving the ground a chance to hold onto it. In the case of the desert, the ground is too hard-packed and dry to absorb the water properly.
In sum total, though, neither Joshua Tree nor LA receive much water at all. This means there’s a fine line between the thriving wild prickly pear cacti around LA and the pained cacti of Joshua Tree.
The cactus is able to survive both environments, so I can use it to tell:
When shriveled and still alive, there’s probably around 6 inches of rain a year, or a similar frequency to Joshua Tree. When it’s thriving, there’s 2 feet or so, or rain similar to LA. In between the two ranges, I’d imagine more and more of the cactus to fill in with green, the glochids to hang on, and for the plant to get taller. If it’s dead, there’s probably been less than 5 inches in the last year (or however long it takes these to finally fade).
This plant perfectly shows the different weather profiles of each region.
A sturdy little rain meter.
A while after the next rain, I’ll head on up to JT to see how these cacti are filling out and whether they’ve survived. I’m curious.
I tend to enter Joshua Tree from the West entrance when traveling from LA. Just set your maps for the Visitor Center and then turn down Park Boulevard a few miles. There’s a great coffee shop on the corner that I always make sure to stop at – the temperature of the drink being the opposite of the weather. This isn’t a sponsorship, I just have a caffeine habit.
Make sure to bring plenty of water, regardless of the weather. The air is a great desiccant up there, as the cacti can show. If you take nothing else from this blog, take this – It’s dry in the desert.