The glorious paper birch outside the window that has for the past three weeks beamed a sunny glow is losing its luster, one golden coin at a time. The 10,000 solar panels the tree has worn since early spring are releasing their grip without a sound, and spiraling to the forest floor.<\/p>\n
In deciduous plants, senescence means about the same as what it does in humans — the process of deterioration with age. Senescence makes me wonder what white-haired person is looking back from the mirror. Trees and other plants are simply shedding what no longer suits them.<\/p>\n
Trees blazing with color are responding to fewer hours of sunlight. Sensing that the days are getting too short for their leaves to efficiently (and magically) change sunlight into tree-feeding sugars, trees like birches and aspens and willows have stopped flooding their leaves with chlorophyll.<\/p>\n
With the cut-off supply of chlorophyll — a green, energy-converting chemical — leaves get to show the red and orange and yellow pigments also present in their cells.<\/p>\n
Why do leaves have the makings for different colors inside them? That’s a good question. Some scientists think that colors like red within them might act as a sunscreen to keep leaves from getting overexcited by photons.<\/p>\n
Though they linger for a few weeks, those lemon-colored birch leaves will eventually let go. When a tree senses it has reached a threshold of daylight hours, cork-like cells develop where a leaf attaches to a stem. This “abscission layer” forms until the artery clogs and hardens. The leaves wait for a breeze.<\/p>\n
Billions of played-out leaves are now wafting to the valley floor, adding weight and insulation and nooks for insects and nourishment in decay.<\/p>\n
Remaining on the branches, tight-fisted buds will be poised to unfurl into leaves next spring. If they don’t first find themselves thawing in the belly of a December moose.<\/p>\n