Large, old Pennsylvania trees grow fastest, storing more carbon

Jeff MulhollemFor those who don't know, Pennsylvania is the hardwood capital of the world. Keystone State forests produce more board feet of cherry, oak, maple and other prized hardwood than any others.

One problem with our vast forests – especially on public lands – the majority of the trees are about the same age, dating back to when huge lumbering operations clear-cut the mountainsides circa 1900. That’s a problem because extremely mature forests produce way less food for wildlife, such as white-tailed deer.

We have millions of big, old trees. And it turns out that they are getting larger, faster than we thought. A new study recently published in the journal Nature reveals that trees do not slow in their growth rate as they get older and larger — the way animals do – instead, their growth keeps accelerating.

"This finding contradicts the usual assumption that tree growth eventually declines as trees get older and bigger," said Nate Stephenson, the study's lead author and a forest ecologist with the U.S. Geological Survey. "It also means that big, old trees are better at absorbing carbon from the atmosphere than has been commonly assumed."

An international team of researchers compiled growth measurements of more than 673,000 trees belonging to more than 400 tree species across six continents, calculating the mass growth rates for each species and then analyzing for trends across all of those species.

The results showed that for most tree species, mass growth rate increases continuously with tree size – in some cases, large trees appear to be adding the carbon mass equivalent of an entire smaller tree each year. That's an eye-opener!

This continuously increasing growth rate means that on an individual basis, large, old trees are better at absorbing carbon from the atmosphere. Carbon that is absorbed or "sequestered" through natural processes reduces the amount of carbon dioxide in the atmosphere. Some claim that gas is causing the Earth's climate to warm.

The research findings suggest that large old trees play a disproportionately important role within a forest’s carbon dynamics. Here in the midst of Penn’s Woods, that is somehow comforting.

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