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Trees and Pollen

Pine (Pinus sylvestris) releasing pollen into the wind.
Ann-Sophie Qvarnström
WikiMedia Commons
Pine (Pinus sylvestris) releasing pollen into the wind.

You’ve heard of counting tree rings: One ring for every year of the tree’s life.

But if you want to understand the long-term history of a whole forest, you’ll need the help of a palynologist, a scientific detective who use tiny pollen grains as clues to help reconstruct the forest’s history over thousands or even millions of years.

Pollen is the perfect clue for two reasons: First, it’s basically the fingerprint of a species. At the microscopic level, every grain of pollen has a unique and identifiable structure.

Second, pollen stays true to its original shape over millennia because its shell is made of a highly resistant compound called exine. When trees release their pollen, the grains drift through the air, settle on the surfaces of nearby lakes and sink to the bottom. Over centuries, those grains of pollen become covered with sediments.

To get samples of this ancient pollen, palynologists plunge metal augers into the lake bottom and extract the sediment that contain the preserved grains. Then, they freeze and slice them into very thin sections, counting up each species’ individual pollen grains under a microscope.

That creates a picture — called a pollen diagram — of the communities of plants that once grew around that lake. And by knowing the environments of where those plants grow now, these pollen detectives can infer what the climate conditions were in that place long ago.

What can pollen records tell us about our own environment? Today, we consider the Great Salt Lake as one huge body of intermixed water and minerals. But pollen diagrams suggest that starting one million years ago, the North Basin and South Basin differed substantially in their water cycles, their chemical properties and the crustacean communities they supported.

So, the next time you sweep pollen off your car or deck, just consider that they are actually tiny packages that can hold big answers.

Dr. Nalini Nadkarni is an emeritus professor of both The Evergreen State College and the University of Utah, one of the world’s leading ecologists and a popular science communicator. Dr. Nadkarni’s research and public engagement work is supported by the National Geographic Society and the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. @nalininadkarni
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