Rain Trees

There’s a kind of tree known commonly in some parts of the world as “rain trees”. The botanical name for these trees is Albizia saman. According to Wikipedia, “The name ‘rain tree’ was coined in tropical India, especially Bengal. Its origin is the moisture that collects on the ground under the tree, largely the honeydew-like discharge of cicadas feeding on the leaves.”

However these are not the trees I want to talk about in this post.

One of my favorite places to hike, at least partly due to its close proximity to my residence, is a particular lake in San Luis Obispo county, California. Unfortunately, due to the drought, the lake is almost completely dried up right now, and has been for some time. Though still some water at the northern end, really, it’s just a shadow of its former self, which is sad because when there is water it’s actually quite a lovely, peaceful place.

There is a unique phenomenon at this lake that I have enjoyed witnessing over the years, but it’s a phenomenon that, at the moment at least, is a bit of a head scratcher. We’ve a species of pine tree that grows here, and roughly surrounding California’s central valley, (a lower montane area called the California interior chaparral and woodlands ecoregion – elevation between 300-3000 ft.) commonly known as “digger pines“, Pinus sabiniana, (though as that name is considered pejorative, it goes by a bunch of other common names as well: foothill pine; gray pine; grayleaf pine; ghost pine; bull pine; sabine, etc.), and there are lots of them at this lake. They’re beautiful to look at, standing tall and proud, and kind of mysterious too. But you already know that’s my way of thinking. 😉

So what is the “phenomenon” of which I speak? This: I have noticed that some of these trees, those next to river banks in particular, actually rain very tiny droplets of water down from above. These are minute in size, yet in total abundance it’s like a shower, a lilliputian rain! I first noticed it when I happened to feel the smallest of drops hitting my face while I was walking beneath them years ago. If distracted one could easily miss it. I stopped and looked up, but there was not a cloud in the sky. Then where…

To see this rain, the sun needs to be positioned above, but opposite you, to light the drops, and there should be a dark background, like thick forest, behind them for contrast. It’s the lightest of sprinklings sizewise, yet thousands of micro-droplets are silently falling around you, quite a wonder to behold. Today, I finally caught it on a video camera and got some screen shots. (My apologies for the shakiness of the videos – as I lack a tripod to steady the camera, my shoulder had to do as my daughter filmed.)

I also took some pics. Click to enlarge.

What might be causing it? My guess is that, as the particular trees I see this lilliputian rain coming from are tall and narrow, that they have long taproots which reach down into the water table next to the river, bringing the liquid up and distributing it throughout the tree, which is normal, but then they are releasing the rest as a visible excess. I haven’t noticed it for some time since we’ve been in a drought and the lake is dry, but a few days ago we had a real rain (you remember Californians, that stuff that falls from the sky?) and so now it’s back. When there’s water in the river, it’s a regular occurrence.

Wanting to know, I made some inquiries at the local university and was directed to Matt Ritter, Ph.D. Professor and Director, Cal Poly Plant Conservatory. Matt suggested that it might be honeydew from aphids, a tiny insect that excretes the stuff from its back end, which, if true, would tend to take the mystique out of it :/. But, though I’m no expert, I’ve not seen any evidence of aphids, no insects, none of the soot that usually results when aphid honeydew gets old and dusty, and no train of ants to feed from and protect their little herd. I also sent links to the videos and pictures. Matt replied “Wow. So weird.”, “This is a peculiar phenomenon indeed. I forwarded your message on to David Keil another botanist in my department and he wasn’t sure what it was either.”

It was suggested that I call Chuck Woodard, the resident ranger at the lake. Interestingly, Chuck told me that he, too, has witnessed and marveled at the tiny rain from these trees, and knew of their precise location. His feeling is that this may be an unusually heavy respiration going on, something perhaps unknown to science.

Anyway, until I discover that these are mass aphid droppings, in the manner of Albizia above, landing on my face, I’m sticking with water – rain. A gentle touch of beauty from nature.

You know, Pinus sabiniana has so many common names already, can I add another?

Rain Trees.

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Later cogitations: The areas where this pine grows surrounds what used to be a giant lake, Lake Corcoran (also Lake Clyde) it’s called.

Areas where Pinus Sabiniana is found.

Another:

It’s also found along the Salinas river*, where, of course, water flows.

That makes me wonder if it evolved as a riparian tree, but has adapted over time to the now drier state.

If so, maybe we can toss in yet another common name, Corcoran Pine.

It’s all just interesting hypothesis at the moment until a proper study is done. BTW, I may have witnessed this without the trees around, so who knows?

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* The Salinas river in San Luis Obispo and Monterey counties.