A century of warming extends growing seasons by a month

What is it about?

Our work shows that forest growing seasons have gotten longer by roughly a month in the past century in the midwestern United States. A historic data set of spring leaf out and autumn leaf coloring of native trees collected by a farmer named Thomas Mikesell in Wauseon, OH from 1883-1912 let us document the timing of growing seasons over a hundred years ago before major global warming. After finding Mikesell's farm plot, we used modern observations of the same species in the same location to determine if global warming has changed how our forests function. We found that Wauseon has gotten significantly warmer since Mikesell's time, particularly in the spring and winter and consistent with global warming. Five of the seven species we investigated had significantly longer growing season than a century ago.

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Photo by kazuend on Unsplash

Photo by kazuend on Unsplash

Why is it important?

Global warming is changing the functioning of natural systems around the world. One of the challenges in documenting these changes is finding high-quality data about how ecosystems functioned before significant warming. Historic data sets provide time capsules into the past and are quite uncommon in North America. By coupling Mikesell's pre-industrial observations with modern observations we had the rare opportunity to provide a detailed investigation of how global warming has profoundly changed the timing of forest seasons. Changes in growing season length are particularly important in understanding how much forest activity will mitigate the effects of rising carbon dioxide, the primary greenhouse gas causing global warming. Growing season length is one of the factors that determines how much carbon dioxide is drawn out of the atmosphere by plants during photosynthesis.

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