Fall Foliage - The Basics (and a little more)
By Michael Pirhalla on November 11, 2011, 12:00am
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With scorching summer temperatures subsiding to cool days and crisp nights, it is not surprising why autumn is a favorite season among many residents of Connecticut. The oppressive humidity has also backed off, leaving behind some of the most pleasant weather of the year. Besides the relief of the summer heat, perhaps the most anticipated natural phenomenon of the autumn season is the fall foliage. Leaf peepers flock to all portions of New England to gander at the leaves and marvel at their fleeting beauty.
However, what causes the leaves to change from green to vibrant oranges, yellows, or reds? And why is the foliage more impressive in some years than others? This year in particular we have seen a relatively late transition, while many leaves have already turned brown and fallen off. Why did this happen? I'll have an answer for all of these questions, but first let's learn a little bit about the color changing process.
The leaves of all deciduous trees and shrubs are tinted with a green pigment called chlorophyll. This gives them their natural green color during growing season. A tree takes in water from the ground, absorbs carbon dioxide from the air, and then uses the sun's solar radiation to start photosynthesis. Chlorophyll helps make photosynthesis possible. However, by late summer the days become shorter and shorter, which restricts the amount of sunlight the tree is able to absorb. Chlorophyll production slows as nights become longer. The bright green tint fades away and slowly transitions into yellow or orange. Some of these pigments, called carotenoids, have been in the leaves all along. They are just masked by the green chlorophyll. These carotenoids provide us with the extraordinary colorations of yellow, brown, and orange.
The bright red and purple colors, which are evident in sugar maple trees, are a result of another type of pigment in the leaf called anthocyanin. This is not present in the leaves for the entire year, but instead is produced at the end of the summer. Complex interactions with glucose levels disrupt the sugar breakdown process after photosynthesis stops, which helps develop anthocyanins.
Weather factors such as temperature, sunlight, and amount of rainfall affect the color vibrancy or length of change. A moist growing season followed by cool, sunny autumn days and chilly nights usually helps to develop the best and brightest colorations. Frost and temperatures below freezing at night, stress the leaves by disrupting their color changing process within the leaf, and lead to early release from the branches. Periods of drought in the late summer or early fall could also trick the leaves into preparing for winter, causing them to not reach their full potential.
Scientists have agreed that heavy rains, drought conditions, and temperature extremes cause dramatic year to year fluctuations in foliage. 2011 for example, was full of conditions that hindered vibrant tree color. Heavy rainfall events occurred in the spring, followed by the extreme weather from Tropical Storm Irene. Connecticut generally picked up over half a foot of rainfall, while some places received upwards of 10 inches. The deluge has caused fungal growth on trees, making their leaves turn brown and fall off earlier than normal. Also, winds from Irene in excess of 50 or 60 miles per hour stripped the leaves off of many trees, thinning out their color changing potential.
The combination of rainy weather and a warmer than average autumn delayed fall foliage this year. If you desire to see really spectacular colors, check out northern and central New England where the leaves are always out in full force!
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