Friday, September 16, 2005

Botanist and Foresters -- global warming and autumn leaf anomalies

Hey, I think I'm beginning to catch on to this Blogging thing. If I want anyone to find these rantings I need to have important search terms in the title! So now you're thinking "uh, oh" this probably doesn't have anything to do with "global warming." The fact is I don't know, that's really my question. Are there any biologists out there -- especially botanists --- who can addres my questions about the changing of the autumn colors?

I have lived in eastern Kentucky in the Appalachian Mountains for nine years -- for the geologists in the audience -- that's just to the west of the great uplift fault that forms at least part of the Kentucky/Virginia border. For seven years before that I lived just on the other side of that fault in Virginia. So I've had sixteen years of annual observation. And what I've observed over that time is a gradual earlier and earlier appearance of color. One particular type of tree has been my bellwhether; it shows brightly colored leaves earlier than other trees in the forest, and has demonstrated this pattern of earlier and earlier color over the past 16 years. Part of my problem is that I can't pin down the type of tree. I'm fairly certain I'm looking at something in the horse chesnut or buckeye family -- with five to seven obovate leaves in a fan like cluster. The catch is that the leaves of these trees turn scarlet -- not yellow -- and all the reference books depict bright yellow fall leaves for all of this tree family in my region. I was actually thought for a while thinking they were black tupelos (same leaf shape and red fall color, but the leaves aren't grouped in that tell-tail fan like configuration).

Putting aside for a moment what type of trees these are, I have been observing them begin to show branches of brilliant red as early as August in recent years, way ahead of the rest of the forest. Then this year, every example of these trees in my entire county fully turned color (flaming scarlet) from top to bottom by the first week in August. Other tree species, such as maple, which used to hit bright red in early to mid-October, are showing their colors now, in middle September. The sycamores, usually the last to go, have turned yellow everywhere.

That's the observation. Here's the questions. Why is this happening? It's not a one year phenomenon, but a decade long trend. What does this observation say about the mechanism of autumn color? As a school child I remember learning that it was "jack frost" (i.e. the first frost of the season) that brought out the brilliant colors (especially the reds and oranges). But this early color trend is appearing along side increasingly warmer Augusts and Septembers. We've got a lot of brilliant red color on the hills, and the night time temperatures have not dropped below 58 degrees at my altitude where I'm observing this color. Obviously it can't be shorter days (days in August and September are the same length they've always been).

Is it possible the autumn color change is triggered by any kind of stressor -- not just cold, but unusual heat, or drought? Or, here's my pet theory, does it have to do with the total amount of solar radiation (light) absorbed (rather than the length of day)? Some time in the past few months I read report by climatic scientists saying that the amount of sunlight reaching the norther hemisphere was actually declining due to increased water vapor and cloud cover (which itself might be due to warming).

While other types of indicators (animal migrations) seem to be suggesting a later start to fall in the far north of this continent, could other factors (environmental stressors or decreased sunlight) result in earlier fall colors and leaf loss?

My question of the day!

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