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Several species of the tree genres Betula have a white bark,especially when they are young. This is quite peculiar to trees - at least in central Europe; so I'm wondering if there is a ecological reason behind it.

The first idea I have is that they protection against the sun. But normally protection of nature against the sun is to make the opposite: put more pigments in the skin, so that the sun does not damage the underlying DNA. If this is the explanation, how do other tree species protect against this?

David
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and-bri
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  • They produce a rare pigment of white color, called betulin. Found the article about it: https://tmtml.blogspot.com/2017/12/why-birches-are-white.html – Robert Lomeno Dec 24 '17 at 14:48

1 Answers1

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It is protection against rapid warming of the cambium layer. A lot of far northern timber has light colored bark which reflects sunlight. The rapid heating from very cold after sunrise can actually damage or even split the bark of dark colored species. This is called sunscalding.

Remi.b
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John
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    Note that aspens, which grow at high elevations in the mountains, also have very light-colored bark. But oddly enough, the conifers growing in dryer areas at the same elevations generally have dark brown to greyish bark. – jamesqf Dec 24 '17 at 20:01
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    conifers of course provide their own year long shade. – John Dec 24 '17 at 22:17
  • Not usually around sunrise, unless located in a dense stand. – jamesqf Dec 25 '17 at 03:43
  • @jamesqf thick, rough or rugose bark also aids in resisting it, conifers also experience less dramatic dormancy which helps resist the effects. Different solutions to the same problem. – John Dec 26 '17 at 01:21
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    The definitive study seems to be Karels, TJ & Boonstra, R "Reducing solar heat gain during winter: The role of white bark in northern deciduous trees" Artic vol 53 no 2 pg 168 (2003). – Bryan Hanson Dec 26 '17 at 21:47
  • There is also a lot of other circumstantial evidence supporting this theory. The birch species that exhibit white bark, in N. America, B. papyriferia, B. populifolia, and B. cordifolia, are all pioneer species inhabiting barren, open habitats and thus exposed to more light. The more shade-tolerant, forest-dwelling birches, B. alleghaniensis and B. lenta, have darker bark, probably because their habitat has more tree trunks to absorb or block out the light so they didn't face the same selection pressure. Also what @jamesqf said about Aspens fits this pattern: they are also pioneer species. – cazort Dec 15 '21 at 16:41