The Shifting Window of Growing Seasons


spring_and_autumn_timing_20002015.jpgObservers know green leaves don’t appear at the same time every spring, nor do they begin to fade away at the same time every fall. To gain a better understanding of the variation in the timing of spring and autumn across a diverse mountain landscape, Eastern Threat Center research ecologist Steve Norman led a study focused on the Great Smoky Mountains National Park. Along with Center research ecologist Bill Hargrove and biological scientist Bill Christie, he analyzed changes in vegetation greenness — or land surface phenology — from satellite-based data collected daily between 2000 and 2015. Researchers used the ForWarn monitoring and assessment tool to view the data on maps generated every eight days. Findings, recently published in a special issue of Remote Sensing, indicate that the timing of spring vegetation greenup and autumn browndown in the Park can vary by about two and a half weeks each year. In general, spring warmth accelerates vegetation greenup, and early autumn warmth delays browndown. Land surface phenology in the Park may also depend on cross-seasonal weather. And elevation appears to drive greenup and browndown more so than moisture. Study results can help resource managers understand ecosystem productivity, anticipate wildlife movement and behavior, and prepare for potential disturbances, such as growing season insect defoliation and wildfire activity. This insight is also useful for planning around the timing of spring flowering and autumn foliage, which are huge draws for recreation-based tourism and critical for local economies. Read more in CompassLive...

Pictured: Vegetation greenness rises and falls each year in the Park’s deciduous forests. Researchers found that spring greenup and autumn browndown can vary by about two and a half weeks each year. Click to enlarge.


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