Autumn is in full swing, and the Northeast US is a riot of colors. What causes this seasonal change? We’ve got the answers to all of your fall foliage questions here:
WHERE DO LEAF COLORS COME FROM?
Leaves are green in the summer because they contain a great deal of the pigment chlorophyll. Chlorophyll is necessary for the process of photosynthesis, which plants use to make food.
Chlorophyll is not the only pigment in leaves, but during the summer there’s so much of it that no other colors can be seen. Leaves also contain carotenoids—yellow, orange and brown pigments that give color to such foods as carrots and bananas. In the fall, some leaves produce red pigments called anthocyanins, which are also found in fruits like cranberries and blueberries.
WHAT TRIGGERS A LEAF TO CHANGE COLOR?
As autumn approaches, days become shorter and nights grow longer. Trees respond to the decrease in sunlight by slowing down production of the green pigment chlorophyll. As the amount of chlorophyll drops, yellow, orange and brown pigments (carotenoids) become visible. In some trees, dwindling light levels cause other changes inside the leaf. For instance, the concentration of sugars often goes up, which causes the formation of red pigments (anthocyanins).
DOES WEATHER AFFECT AUTUMN COLORS?
Only a little bit. Although some people assume that leaves change color in response to cooler weather, it’s really the shorter days of fall that signal to trees that it’s time to prepare for winter. But weather does affect the intensity of leaf color. Seasonably warm and sunny fall days combined with cool (but not freezing) nights seem to produce the most stunning autumn colors. In addition, fall colors can be delayed by a severe summer drought.
DO LEAVES ON ALL TREES CHANGE COLOR?
No. Trees like pines, spruces and firs are “evergreens”—their leaves are always green. These trees generally have tough needle-shaped leaves that can withstand cold weather. In fact, individual leaves on evergreens can stay on the tree for several years.
ARE CERTAIN COLORS ASSOCIATED WITH A PARTICULAR KIND OF TREE?
Yes. The chart below lists some common trees and their typical fall leaf colors.
BEECH: Yellows and Tans
DOGWOOD: Deep Reds
OAK: Reds and Browns
RED MAPLE: Bright Reds
SOURWOOD: Deep Reds
SUGAR MAPLE: Orangish Reds
Can’t get enough fall foliage? Check out our Pinterest board Autumn at the Museum.