By John Thompson
as seen in the 2018 Fall Newsletter

Most marvel at the color saturation of October’s "peak foliage"— but the astute leaf-peeper appreciates the Season’s progression of color

beginning with red and yellow flashes in late summer and extending through November’s flickering gold.  The first colors that we begin to see in the late summer are often diseased, injured, or drought-stressed trees, but frequently there will be scattered red maples in some of our swamps that begin to turn red by early September.    

Bright fall sunlight produces the most brilliant foliage

Why do leaves change colors? Pigments are most responsible for the color changes we see in autumn: chlorophyll, carotenoids and anthocyanins.  

Chlorophyll allows plants to produce sugars from sunlight.  As the days shorten, the trees stop producing chlorophyll and store valuable sugars and nutrients for the following year.  The reduction of green chlorophyll in the leaves allows other colored compounds to show through. Carotenoids show up as yellow and anthocyanins show up as red.  

One of the earliest wide-spread colors that we see is yellow from ash, yellow birch and black birch. Red maples generally will turn red, while their cousins, sugar maples will show a spectrum of yellow, orange and red.  We generally recognize “peak foliage” as the period when maples are in full color.  Oaks will be the last to change, with red oaks turning red and chestnut oak golden to bronze hues. 

The northern hardwood forest is the predominant forest in the Catskills and includes tree species with the most dazzling colors.  Sugar maple and beech dominate this forest; other common trees include yellow birch, red maple and black cherry.  Locally, there is white ash, American elm, basswood, and hop hornbeam.  

A common question this time of year is, "When is peak foliage going to be?"”Answering this question is tricky, because while some factors that play into the timing of foliage are constant, many change. Different species turn different colors, and those species turn at different times in the fall.  Two constants are 1) day length, which is the primary factor influencing when leaves change, and 2) the tree species, which is the main factor influencing how the leaves change through a predictable color progression.  But environmental conditions and weather play into the timing of foliage change.  

Perfect foliage follows the Goldilocks principle: that the weather has not been too hot, too cold, too wet, nor too dry, but just right. The entire growing season contributes to the health of trees and their colors, but bright fall sunlight produces the most brilliant colors. Numerous cloudy days during fall may result in more golds and yellows. If temperatures get too cold, leaves may die before they change colors. Heavy rains and winds during fall knock leaves off of their branches and shorten the leaf-peeping season.  Climate change is another variable and is causing the fall foliage season to be later in the season.