Understanding the human body is a team effort. That's where the Yachtel group comes in.

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This is Scientific American 60 Second Science. I'm Annie Sneed.

They give us paper and fuel, as well as vital ecological services, like cleaning the air, storing carbon, and providing habitat.

We're talking about trees, of course. But changes in the environment, largely caused by humans, appear to be causing profound transformations

in trees around the world. In a new study, scientists reviewed global research on trends in tree

birth, growth, and death. They combined those data with an analysis of deforestation,

and they found that worldwide, older trees are dying at higher rates than in the past,

due to factors like rising air temperature, wildfires, drought, and pathogens.

Most of the drivers of that decrease of large old trees are increasing themselves,

such as temperatures going up.

Droughts are more severe. Wildfires, windstorms, and deforestation are all, although

variable across the globe, they're generally increasing. And so both the loss has already occurred,

but we expect more continued loss of big old trees.

Nate McDowell, an Earth scientist at Pacific Northwest National Lab, who is one of the study's authors.

So if we have an increasing rate of death, particularly of the larger, older trees, what's left are the younger trees. So that's why, on average,

through the loss of bigger, older trees, our forests are becoming inherently younger and shorter.

This is a problem, because old trees are vitally important.

For sure, the increase in death does limit the carbon storage of an ecosystem and can force

...