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Science in the summer

The growing season is a time for the Arboretum’s researchers to grow knowledge. Take Forest Ecologist Robert Fahey. His job is to understand how forest ecosystems work, and this summer, it will take him to northern Michigan.

He is trying to gather data that will show how much carbon forests store at different ages. The question is related to climate change, because trees remove carbon dioxide — a potent climate-change gas — from the atmosphere.

Trees use carbon dioxide in photosynthesis, the chemical process by which they make food, and store the carbon in their roots, trunks, branches, and leaves.

When forests are young and actively growing, they absorb lots of carbon dioxide, Fahey says. Most of the upper Midwest’s forests are no more than 80 to 150 years old, because the older trees were logged out when settlers arrived. As new trees grew up, they have been helping to slow the rate at which carbon dioxide builds up in the atmosphere.

But older forests may not absorb as much carbon dioxide, he says. That’s because some trees will age and die, and as their wood and roots rot, the carbon they stored is released.

The question is, how much? This summer, Fahey will be in some of the few patches of forest that were never logged. In these mature forests, trees have been sprouting, growing, living, and dying since the retreat of the last glacier 10,000 years ago. He will be measuring and taking samples from old trees, trying to quantify how much carbon an older forest captures. That will give a clue about what to expect from our younger forests as they age.

This sort of basic knowledge can eventually help the caretakers of natural areas and policymakers as they make decisions about caring for and including trees of different kinds and ages in the landscape.