The Shifting Window of Growing Seasons

When winter comes to an end, it’s no mystery that warming temperatures and spring rains bring new life. Wildlife emerges, flowers bloom, and brilliant green leaves begin to fill the ground and the forest canopy—all part of their seasonal cycle known as phenology.

Observers know those green leaves don’t appear at the same time every spring, nor do they begin to fade away at the same time every fall. U.S. Forest Service and Park Service researchers now have a better understanding of the variation in the timing of spring and autumn across a diverse mountain landscape in Great Smoky Mountains National Park.

Research ecologists analyzed changes in vegetation greenness — or land surface phenology — from satellite-based data collected daily between 2000 and 2015. The monitoring still continues.

“The Great Smoky Mountains National Park supports rich vegetation communities and other biodiversity due to complex terrain and ample rainfall, though seasonal variation in temperature and precipitation is considerable from year to year,” says Norman. “We examined the influence of seasonal weather variation as well as forest cover types, topography, and disturbance history on the Park’s land surface phenology.”

The researchers determined that the timing of spring vegetation greenup and autumn browndown in the Park can vary by about 2 and a half weeks each year. In general, spring warmth accelerates vegetation greenup. Early autumn warmth delays browndown.

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