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The Coniferous Albedo (or evergreen albedo if you prefer)


Sutter Bob

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If the title didn't scare you off you must know what I'm getting at. I wanted to share my excitement at understanding a new word. Interestingly, a search of Palm Talk has only a few references to albedo and most have been from a more macroscopic perspective. With thanks to Wikipedia I now feel more enlightened (Did my albedo just shrink?).

In a nutshell, albedo is the ratio of reflected radiation from a surface to the incident radiation upon it.

Those of us who struggle to grow palms in the so-called temperate latitudes all too quickly realize the value of canopy.

My still naive understanding of canopy has evolved a bit from thinking that overhead cover acts as a simple mechanical frost blanket as it were, somehow keeping crystals of ice from falling out of the sky and landing on the tender leaves of my sacrificial tropical icons.

While reading the recent threads on thermogenic plants and selection of trees for canopy, I began to appreciate more than ever the value of canopy in keeping many of my prized thermophiles alive through our frosty winters. Clearly, a tall evergreen is more than just an old sheet thrown over these unsuspecting exotics (at least an old white sheet).

What else is going on? One element of the value of canopy probably has to do with absorbance of incident radiant energy and subsequent release to the local environment. I assumed this energy sink effect is more valuable than intrinsic thermogenesis and this led me to learn of the concept of albedo.

I have been especially impressed at the difference the proximity of a coniferous tree can make in the survival of palms here. As it turns out, such trees have a very low albedo, and therefore absorb a considerable amount of energy into the local environment.

A lot of words to remind me that black asphalt gets pretty hot when the sun shines on it.

http://en.wikipedia.org/wiki/Albedo

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Evergreen forests have an even better ability to retain heat. The conifer rating on Wikipedia is for Summertime.

The main function of canopy during a freeze is to reflect the IR from plants below back to your plants. This is very useful during a radiational freeze.

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Good info - thanks Bob.

Yet more reasons to plant more trees and then more palms...

Cheers,

Jonathan

South Arm, Tasmania, Australia - 42° South

Mild oceanic climate, with coastal exposure.

 

Summer: 12°C (53°F) average min, to 21°C (70°F) average daily max. Up to 40°C (104°F max) rarely.

 

Winter: 6°C (43°F) average min, to 13°C (55°F) average daily max. Down to 0°C (32°F) occasionally, some light frost.

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