Autumn Arrives


Provo, UT—Each year’s Autumn arrival brings with it a plethora of new colors. Utah sees a surge of reds, yellows, and oranges, beginning at the mountaintops and descending gradually to the valley around early to mid-October. But many are unaware of what causes this vibrant transformation, and why it occurs. BYU Ecology professor Sam St. Clair explains the science behind the season.

“The plant has an internal clock that tells it when it should be doing things, so it can anticipate when changes occur,” St. Clair explained. The trees “sense day length, and know when October is coming, based on shorter days,” St. Clair said.

This internal clock, a sort of botanical intuition, triggers a process called senescence, in which a leaf’s hues dissolve one on top of another, revealing each successive underlying layer. However, this process is more than a photogenic phenomenon. It is quite literally a survival instinct.

“The changes in the leaves, in the colors and the pigments [are] a chemical strategy to survive when you can’t move…that’s one of the really fascinating things about plants,” St. Clair said. “If I took 100 humans up on Y Mountain and said ‘you can’t move for 5 days,’ we’d come back and they’d all be dead. But there are literally millions of plants up on that mountain that thrive because of their creativity.”

Professor St. Clair and his botany students look forward to watching the valley illuminate with color over the next few weeks.

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