Across a Continent, Trees Sync Their Fruiting to the Sun

European beech trees more than 1,500 kilometers apart all drop their fruit at the same time in a grand synchronization event now linked to the summer solstice.

Meghan Willcoxon at Quanta: Each summer, like clockwork, millions of beech trees throughout Europe sync up, tuning their reproductive physiology to one another. Within a matter of days, the trees produce all the seeds they’ll make for the year, then release their fruit onto the forest floor to create a new generation and feed the surrounding ecosystem.

It’s a reproductive spectacle known as masting that’s common to many tree species, but European beeches are unique in their ability to synchronize this behavior on a continental scale. From England to Sweden to Italy — across multiple seas, time zones and climates — somehow these trees “know” when to reproduce. But how?

A group of ecologists has now identified the distinctive cue — what they call the “celestial starting gun” — that, along with balmy weather, triggers the phenomenon.

Their analysis of over 60 years’ worth of seeding data suggests that European beech trees time their masting to the summer solstice and peak daylight.

It’s the first time scientists have linked masting to day length, though they still don’t know how the trees do it. “It is striking to find such a sharp change one day after the solstice. It doesn’t look random,” said Giorgio Vacchiano, a forest ecologist at the University of Milan who was not involved in the research.

If further research can show exactly how trees sense daylight at the molecular level, “that would be truly spectacular,” said Walt Koenig, a visiting fellow at Cornell University and a retired research zoologist from the University of California, Berkeley, who wasn’t involved with the study. The discovery of the genetic mechanism that governs this solstice-monitoring behavior could bring researchers closer to understanding many other mysteries of tree physiology.

More here.

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