Wednesday, February 25, 2009


When Leaves Fall

Do deciduous trees shed their leaves at random or in some predictable order? If in order, is distance from root or trunk a factor? Do the topmost or outermost leaves fall first, or those nearest the ground or the trunk? If there is a pattern, is it the same for all species? Perhaps the answers are obvious and well-known, but I haven't observed or investigated closely enough to know. The questions came to mind when I read Thomas Hardy's The Upper Birch-Leaves:
Warm yellowy-green
In the blue serene,
How they skip and sway
On this autumn day!
They cannot know
What has happened below,-
That their boughs down there
Are already quite bare,
That their own will be
When a week has passed,-
For they jig as in glee
To this very last.

But no; there lies
At times in their tune
A note that cries
What at first I fear
I did not hear:
"O we remember
At each wind's hollo-
Though life holds yet-
We go hence soon,
For 'tis November;
-But that you follow
You may forget!"
Henry David Thoreau in his Journal (October 22, 1858) confirms that birches lose their leaves starting at the bottom and moving upward:
The birches are now but thinly clad and that at top, its flame-shaped top more like flames than ever now....The birches have been steadily changing and falling for a long, long time. The lowermost leaves turn golden and fall first; so their autumn change is like a fire which has steadily burned up higher and higher, consuming the fuel below, till now it has nearly reached their tops....Nevertheless the topmost leaves at the extremities of the leaves [sic] are still green.
See also Thoreau's Journal (November 3, 1858):
The only white birch leaves now seen are those lingering green terminal leaves of the 23d [sic], now at last turned yellow, for they are now burnt upward to the last spark and glimmering. Methinks the birch ripens its leaves very perfectly though gradually.

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