We received an interesting bulletin from Penn State that sets forth some of the conditions that are necessary for a brilliant show of fall leaf color. Leaf change is instigated by the dropping of temperatures.
Chlorophyll strops being produced and the xanthophylls and carotenes responsible for the yellows and oranges become visible. Anthocyanins that result in the dazzling reds and purples, seen in maples and sumacs, are produced as the chlorophyll production declines.
The Sunny days and clear cool nights bring on the most colorful show. As the cold destroys chlorophyll it promotes the production of the anthocyanins. Anthocyanin production is halted by freezing temperatures. Night time temperatures in the upper 30’s and 40’s are ideal. Bright sunshine will also destroy chlorophyll and encourage the production of this pigment.
If the weather stays too warm, such as the weather we have been having, chlorophyll production will not stop and the leaves will stay green longer. If the night temperatures do not drop enough the anthocyanins will not be produced and the color of the leaves will be predominantly yellow and orange.
A dry September is good for colorful leaves, as the lack of water concentrates the sugar in the tree sap. A high sugar content promotes the production of the anthocyanins. Drought conditions however will cause the premature browning and dropping of the leaves. Hot weather in conjunction with very dry conditions will accelerate the premature leaf drop.
How has our summer of little rain affected our chances of a good fall leaf show? According to Marc Abrams, professor of forest ecology and physiology, “I was worried about the drought that we had into early August, which was really quite severe,” he said. “But then most of the state received significant rainfall, and the drought watch was called off in most counties. Even with that severe July drought, I didn’t notice any early leaf drop or mortality. So we were expecting an impressive fall foliage display.”
He goes on to say that lack of rain in September is likely to result in a poor show of leaf color unless there is a significant rainfall in “another week or two”. This bulletin was issued on October fist and we have had little rain since then. It appears that we are doomed to seeing a less than brilliant show of leaves this year followed by premature browning and the falling of the leaves. According to Professor Abrams this process has already started in Center County.
What may save the leaf display is that the temperatures have finally started to cool. Perhaps Mother Nature will come through with her fall display after all.