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"And the LORD God made ... trees that were pleasing to the eye ..." Gen. 2:9, New International Version.

"Bonsai isn't just something I do; it's part of what I am." Remark to my wife and daughter.

Wednesday, August 8, 2012

Elevation, Light, and Bonsai

     By elevation, I mean altitude, elevation above sea level. At first there would seem to be little connection between altitude above sea level and bonsai care; but in fact there is something to keep in mind. (Actually, two "somethings;" but I'm focusing on just one here.)

Because air is a mixture of gases, its density decreases as one goes higher into the atmosphere. Anyone who has traveled into the mountains has experienced the effect: the higher you go, the thinner the air becomes, and the less oxygen is available in each successive lungful!

This thinning of the atmosphere has another effect. Air acts as a screen, limiting the intensity of the sunlight that reaches the surface. The higher the altitude, the less air there is between the sun and the surface, and the greater is the intensity of the sunlight that gets thru.

I saw that at first hand while growing up. Quito, Ecuador, where I went to school, sits 9300 feet above sea level (2850 meters.) At that altitude, almost one quarter of the earth's atmosphere is below you. Not only is it difficult to walk briskly and converse at the same time. The sunlight is intense enough that we "gringos" could sunburn painfully in as little as 15 minutes, if we exposed skin that was normally under clothing. We learned to use sunscreen when we went swimming, or pay the price!

There's another aspect to this atmospheric screening. As you probably know, longer wavelengths of light -- red, infrared, and longer -- are less effectively screened out by the atmosphere. We see the results in a sunset. When the sun's angle is low, its light has to travel thru a little more air to reach us. Blue-end light is blocked more completely, leaving a greater proportion of red to get thru -- and we enjoy a red (or near-red) sunset.

At high altitude, the same principle is at work, but in reverse. As atmospheric density drops, the amount of red-end light that is blocked drops; but the amount of blue-end light that is blocked drops even faster. The result is that a greater proportion of the light that is received is blue, violet, ultraviolet, and shorter. (Another reason we would crisp so easily in Quito, if we forgot the Coppertone.)

And, in plants, light at the red end of the spectrum promotes stem lengthening, while light at the blue end promotes compactness, smaller foliage, and shorter internodes.

What does this have to do with bonsai?

If you live at a higher altitude and grow trees native to significantly lower elevations, keep in mind that they are getting light that is more intense than they are "programmed" for. Also, the light, being bluer, is more energetic. The effects will be most pronounced when you first move them to your location, but even after adapting they may need more sun protection than they need closer to sea level.

A greater number of us, I suspect, grow trees native to elevations significantly higher than the altitudes at which we live. My yamadori ponderosa pine is such a specimen: it was collected at 5800 feet above sea level, about 1770 meters; and now lives at all of 826 feet, or 252 meters. (Add about 13 feet, or 4 meters, when I take it up to the deck. <wink>) The sunlight that now reaches it is about 85% as intense as what it received in its native habitat. (It is also slightly redder; the color difference is too small to be detected by the human eye, but may have a miniscule effect on the tree's growth.)

The upshot is that, if I want this tree to thrive, I have to make sure it gets as much sunlight as I can possibly give it. I've got it in the sunniest spot available, on our south-facing deck. I will probably add a reflective covering (see my last post) to the wall behind it to increase the amount of overall light it receives. I also have to be ready to do a little more to encourage compactness in this pine.

Atmospheric density, of course, also affects the availability of oxygen, carbon dioxide, and other gases plants need. But that's another topic!

:-)  :-)  :-)

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