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When leaves that are green turn to gold

September 24, 2010

It's autumn! The colors are popping right now in the aspen groves.

Alchemy is a word that can be loosely defined as that which happens when one element becomes another; when one thing transforms to another thing.

In the old days, alchemists were those who strove to turn base metals into gold, although to no avail. Earlier than that, such a transformation would have been called magic.
 
Call it what you will, it’s now: this moment in time, this place, this time of year as green, aspen-covered hills turn overnight to flaming gold and scarlet and crimson.
 
Beginning sometime around Sept. 15 every year, it comes; waves of color moving down the mountains and hills from the highest elevations to the lowest, a brief flaming moment of glorious beauty that ends all too soon, almost exactly four weeks later, when the brilliance is finally dimmed by cold, wind and shortening days.
 
What happens in these amazing trees when the sun backlights the trillions of aspen leaves in our backyard, turning the ground underneath them, the creek flowing beneath them, into a brilliant stained glass window?
 
 Alchemy, pure and simple. Magic.
 
How it happens
 
According to longtime resident and former Bureau of Land Management botanist Anne Halford, it goes something like this.
 
ln spring and summer, aspens, cottonwoods and other deciduous trees convert sunlight to sugar: food for bark and leaf and root. The trees use cells within the leaf called chloroplasts, which make the chlorophyll that accounts for the green color seen in most foliage.
 
In the fall, though, the days shorten and the temperatures grow colder and food production in the leaves begins to slow.
 
When this occurs, the chlorophyll in the leaves begins to break down, leaving behind sugars trapped in the leaves. The sugars form a pigment called anthocyanin, which is responsible for the colors that eventually become apparent. The degree of brilliance and the variety of colors are then dependent on a complex series of events in the environment, including temperature and moisture.
 
For example, warm, sunny days followed by cool nights, with temperatures below 45 degrees, are optimal for both variety and brilliance of color. That’s because the sugar production increases during the day, accounting for better colors. If the night is too warm, however, the colors leach out of the leaves overnight. So cool nights help to preserve the length of the color show. 
 
But the leaves are fussy and finicky. If it gets too cold, say a hard freeze occurs, the colors die, and the aspens turn to brown.
 
Cool, gray days mean leaves make less sugar, so there are less anthocynins available to color the leaves.  And if the year has been a dry one, the leaves tend toward dullness, due to lesser overall vitality in the tree.
 
This year is shaping up to be one of the best in recent times. The wet winter and long summer mean the trees are healthy and vital. A long-term forecast puts the Eastern Sierra on a warm dry spell for another few weeks, although that could change.
 
The backdrop of still-green meadows and snow on the highest peaks is unusual for this time of year, making the coming show one to savor.
 
So go on. Get out there.
 
Rock Creek Road. Drive up the road from Tom’s Place as the sun begins its descent behind the mountains, say about 3 p.m. The higher you go, the better the show.
 
Conway Summit. Head up to the top of the summit, then down the other side until you reach either Green Creek or Virginia Creek Road. Or better yet, make a loop  of the two roads and head up under Dunderberg Peak. The colors there are already glorious and it’s only going to get better. The gravel road is better than it looks; suitable for most 2WD vehicles.
 
Bishop Creek. Head up Bishop Creek to either North or South Lake, or even better, both. Make it in time for Parchers Resort’s all-you-can-eat breakfast on weekend mornings (until Oct. 1). 
 
Lundy Canyon. Head north of Lee Vining up Lundy Canyon. The trees down low are still green, but it’s going to change fast. The upper canyon is justly famous for its color show and should be perfect by late next week.

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