I’m a leaf peeper. At least, that’s what I was called several times on a recent trip to New England. Millions of tourists (spending a combined total of billions of dollars) pass through the northeastern United States each autumn to view the area’s crisp, colorful leaves. However, we had planned our trip without considering the condition of the local trees. This turned out to be for the best because when I checked the fall foliage predictor prior to our trip, it seemed as if we’d arrive a few weeks too late to witness the blazing colors.
We did miss the bright yellows, brilliant reds, and fiery oranges, but not due to our timing. Indeed, the trees were still full of green leaves absorbing sunlight and turning it into fuel. Fall color arrived late this year for much of the country. Why did these little food factories run overtime in 2017?
Timing the fall color
Moisture, temperature, and light play critical roles in determining the turning, or death, of the leaves. According to the Northeast Regional Climate Center, 2017 was the third warmest September on record in Massachusetts, New Hampshire, Rhode Island and Vermont (all states on my whirlwind tour), which encouraged green leafiness. In addition, the hot, dry period in the Northeast in the late summer had a negative impact on the leaf cycle. Lack of rain causes leaves to go from green to brown with far less fanfare in between.
Some speculate that global climate change, specifically, the increasing concentration of carbon dioxide in our atmosphere, is causing a late shift in the timing of the arrival of fall colors, just as it has impacted spring blooms.
Chlorophyll is a critical component of photosynthesis, the process by which plants turn light photons into food. It’s also the substance that gives plant leaves their green color. As leaves stop producing food, the chlorophyll breaks down, giving rise to yellow (xanthophylls) and orange (carotenoids) pigments that were in the leaves all along, but had been overshadowed (or out-colored) by the chlorophyll. Red and purple pigments (anthocyanins) develop later in the summer from sugars that collect in the leaf, creating an especially captivating look.
Not all tree species are created equal when it comes to fall color. Sugar maples (of which there are many in New England) tend to turn a brilliant orange, while oaks hue toward reds and dramatic browns, and aspen and poplars become golden yellow. Take a look at this New York Times graphic of a detailed, highly magnified version of a cross-section of a leaf.
Find the Hidden Colors
Your students can take a different kind of look inside leaves with a relatively simple paper chromatography experiment. With a few basic supplies, they can dissolve pigments and observe the colors as they climb a slip of paper. If you live in a region of the country without a fall color change or it’s already past, no worries. You can also use leftover Halloween candy for a similar experiment.
Dead Leaves are Golden
After leaves have fallen and lost their captivating colors, they are often treated like a nuisance, bagged up and discarded. But they are still golden for your soil. No doubt, young scientists will want to educate their parents on the value of leaving the dead and dying leaves covering the lawn rather than spending hours raking it into tidy, disposable piles.
*The Northeast Regional Climate Center has loads of interesting information for young scientists.