The science behind why leaves change color in the fall


AMHERST, Mass (WWLP) — Autumn in New England is a time of change. Not only for temperatures, your choice of clothing, and the pumpkin harvest but for the reds, oranges, and yellows across the landscape.

The change happens as the growing season comes to an end.

“And whenever the days start to get shorter, the organelles in the plant start to shut down, and we’re most familiar with chloroplast, chloroplast manufactures the green pigment chlorophyll, and they start to shut down around this time of year,” Rick Harper, an extension associate professor of urban forestry at UMass, told 22News.

That shutdown leads to the green color dissipating, revealing the light orange and yellow colors that are hidden beneath the green year-round. The bright red and purple colors are instead manufactured by the leaves in the autumn.

Shorter daylight hours are the primary driver behind the leaves changing color, but the weather plays a part as well.

“When temperatures are warmer, when there’s more moisture in the environment, these sorts of things can all play a role in terms of making the colors more muted, or making them more brilliant,” Harper said.

Foliage generally peaks in western Massachusetts in mid-to-late October. For Springfield this year, it will peak between Oct. 12 to 16, according to Alex Sherman, the City Forester.

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