The Shining

Lichen-covered tree, Tresco, Isles of Scilly, ...
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I have a “weird Uncle Fred” question (so named by my non-biologist coworkers at a remotely-former hospital PT job. They were not infrequently freaked when I’d bring in a living or formerly living thing I’d found between the parking lot and the department to show them.)

Okay–here it is: How many–if any–of you (I suppose even our urban readers can play provided you drive past trees at night) have noticed that (some) trees glow in the headlights of your car?

Well, they don’t glow as in bioluminescent but are reflective of bright white light in the same way that those stripes on running shoes and sweats are reflective–like a road sign.

In my headlights I see a very faintly blue-green cast to the rock and tree surfaces covered by a certain kind of crustose lichens; it’s not uncommon at all. While they are light in color, they appear way brighter than the surfaces where they live.

Why is this so? Does it have perhaps to do with the fact that lichens are sensitive to some wavelengths of UV light and this is a kind of SPF shield against sunburn? I have to wonder at that answer as these lichens are in deep woods. Perhaps the species evolved on open rock bluffs in full exposure. I’m totally supposing.

Lichens are sensitive to certain wavelengths in sunlight. Some lichens are flourescent to longwave ultraviolet light so uniquely that it aides in identification of some of them.

And they can adapt their pigments to make them better able to tolerate UV light. That’s a chemical adaptation not unlike tanning of the skin.

Those are chemical responses to light stressors. But What I’m observing is a physical property, not a chemical one, I’m thinking.

Okay. You are dismissed for now. Report back when you have an answer for me and I’ll add 10 bonus points to your blogbuddy biology score!

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Fred First holds masters degrees in Vertebrate Zoology and physical therapy, and has been a biology teacher and physical therapist by profession. He moved to southwest Virginia in 1975 and to Floyd County in 1997. He maintains a daily photo-blog, broadcasts essays on the Roanoke NPR station, and contributes regular columns for the Floyd Press and Roanoke's Star Sentinel. His two non-fiction books, Slow Road Home and his recent What We Hold in Our Hands, celebrate the riches that we possess in our families and communities, our natural bounty, social capital and Appalachian cultures old and new. He has served on the Jacksonville Center Board of Directors and is newly active in the Sustain Floyd organization. He lives in northeastern Floyd County on the headwaters of the Roanoke River.

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    • This is very interesting, but I don’t think it accounts for what I’m seeing. A search for lichens AND (backscatter OR retroreflecion OR sylvanshine) doesn’t make me think this particular combination of organism and phenomenon have been described. And more to the point, the sylvanshine effect seems to take place from leaves at an angle to the viewer while I’m seeing it on vertical surfaces of rock bluffs and trees. Much appreciated for a new word and natural phenom!