In her delightful book, Red Oaks and Black Birches, Rebecca Rupp explains why leaves change color and then fall. Shortened days and cooler nights encourage the formation of a kind of tourniquet where each leaf stem is attached to its branch. It cuts off the leaf's source of water and minerals, causing in turn the degradation and final disappearance of chlorophyll, the source of the leaf's green coloration. All summer that overwhelming green has masked the colors of other molecules but now those colors come to the foreground. "The yellows and oranges of birches, sycamores, and sugar maples," she says, "are due to carotenoids, the same cheerful molecules that color carrots, corn, egg yolks, and daffodils. Browns also may result from carotenoids or from tannins. Crimsons, scarlets, and purples are due to anthocyanins, which also color red cabbages, red roses, and purple irises.
"Finally that same tourniquet reduces the grasp of the leaf stem until the wind carries the leaf away, leaving a wound where it was attached to its branch. The tree quickly plugs that wound with a cork leaf scar to protect itself from water loss. That leaf scar is as unique to its tree species as is the leaf itself and specialists refer to it for winter identification."
That is what is going on all around us at this time of year. So this is the time to get out into the countryside to enjoy this feast of color.
The annual peak of coloration is influenced by two major factors: weather and climate. Those two words should not be confused. Weather is what our local news analysts talk about: "clouds turning to rain tomorrow, but clearing during the week ahead." Climate is historical: "April showers bring May flowers and the beginning of the growing season." Quite simply, climate is weather averaged over longer periods or, as it has been put another way, "Climate is what you expect; weather is what you get."
Leaves, and maple leaves in particular, are affected by weather. Warm sunny days and cool but above freezing nights favor anthocyanins and this gives us those bright reds, purples and crimsons. The orange, yellow and gold carotenoid colors are more constant from year to year, but early and especially severe frosts work against all leaf colors, giving the tannins an advantage and thus leading leaves to turn brown faster.
I am told that warm, wet springs and summers not too hot and dry produce the best leaf colors. If that is true, I am not encouraged about this year. Our spring was not just wet, we nearly drowned and our summer this year was uncomfortably hot.
Which brings us to climate. One climate factor that does not change from year to year is day length. Clouds produce weather effects, but the progression of shorter days remains the same over millennia. The climate factor that is changing is warmth. Our recent rapid warming is already having an effect on many aspects of our environment. We should soon witness color dates later in the year.
As of now, such changes are masked by weather effects, but spring is another story. The dates when maples produce the sap we boil into syrup have moved earlier. Tim Perkins, director of the University of Vermont's Proctor Maple Research Centre, said recently, "A dozen years ago we started hearing from producers they were tapping earlier and making syrup earlier. So we scoured the records and found that over 40 years, between 1963 and 2003 the opening of the season had moved forward by an average of a week in New England." He added that over that same period the following leaf development is still earlier, now by ten days.
In fact, many foresters are projecting the demise of maples across all of the Northeast as the warmth increases over the next century.
We all love those bright maple colors, but I have two other favorites. One is the bright yellow aspens that appear late in the season in the Southern Tier, their colors in stripes across hillsides between equal swaths of evergreens. And along the southern Appalachian Trail I found quite beautiful the rich bronze of their oaks, very different from anything we see here on the Niagara Frontier.-- Gerry Rising