I was going to write about solar ovens in Africa this week, but I’m still waiting for an interviewee to get back to me. So instead I’m going to talk about… leaves.
Here in Maryland, the forests still look surprisingly green. Now that we’ve had a few cold nights, some of the trees are “trying to turn,” as my husband puts it, but it doesn’t really look like fall, yet. The Weather Channel confirms that the delayed color is both regional and weather-related. That is, it’s not just my autumn that has been delayed, and the delay in foliage is, indeed, because of the extended warm weather.
But I’ve noticed that the leaves are falling.
They’re not falling heavily, yet, though at this point in the year they wouldn’t be. It’s just a few dead leaves accumulating on the sides of the roads and the edges of the sidewalk. But the funny thing is, the fallen leaves are mostly green. The trees they are falling from are also mostly green, but it is a strange green, an altered hue. I wonder–have the leaves changed after all?
“Brown-down,” the technical term for it, is a multifaceted process initiated when shortening day-length triggers the growth of the “abscission layer,” a corky section in the leaf petiole (its stem) that interferes with the flow of water and nutrients. Eventually, the cork gets thick enough to cut off the leaf entirely so it dies, and the petiole breaks neatly at the abscission layer. The leaf falls off. But before all that happens, before the cut-off is complete, the leaf continues to function. But chlorophyll breaks down as it’s used. It has to be continually replaced. With the leaf partly cut off, the chlorophyll can’t be replaced. The green fades from the leaf, revealing yellow and sometimes red pigments. Eventually, those pigments, too, break down, and the color fades.
Temperature changes help determine the speed and intensity of the color changes, even though the growth of the abscission layer itself is governed by day length.
Does this sound familiar?
Years ago, I wrote a post about spring, and how different aspects of spring (leaf-out, hatching of caterpillars, arrival of migratory songbirds) are cued by different factors. As climate change speeds up some of those factors but not others, the entire progression of spring gets out of sync. I’m wondering if the same thing is happening with fall.
If leaf-fall is triggered by day length, and the color change is triggered by temperature, then as climate change shifts the seasonal cooling later and later–and the timing of shortening days can’t change–it stands to reason autumn should get out of wack. Specifically, the leaves will fall more or less on time, but there will be little to no fall color.
Is that what we’re seeing?
I’m engaging in speculation, here, but it seems plausible. The ecological cost of climate change, and ultimately most important (that includes human ecology, FYI), but there’s a psychological cost, too. Personally, I find the weirdness of this non-fall very disturbing.