North Atlantic Oscillation dictates timing of tree reproduction in Europe

"Our work shows that the remarkable synchronization of behavior across such vast distances is linked to the North Atlantic Oscillation," ecologist Andrew Hacket-Pain said.
By Brooks Hays  |  Dec. 20, 2017 at 1:48 PM
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Dec. 20 (UPI) -- Trees synchronize their reproductive schedule with the North Atlantic Oscillation, a climate pattern that influences zonal winds and the strength of storms.

The NAO describes fluctuations in the region's air pressure differences. Shifts in the region's pressure gradients affect atmospheric circulation and Europe's climate patterns.

And according to the latest analysis, the oscillation also affects trees' masting schedule. Masting describes production of large amounts of seeds by trees in a single year.

Previous studies have shown tree populations tend to mast together. If one tree in a forest produces an unusually large number of seeds, it's likely its neighbors will to. Thus, entire forests tend to mast together.

When scientists at the University of Liverpool compared the masting patterns of European beech and Norway spruce with North Atlantic Oscillation, they found heavy seed crops corresponded with high-frequency summer- and spring-NAO and low-frequency winter-NAO phases.

The unique phases explained the simultaneous masting of beech and spruce trees across Europe in 1976, 1995 and 2011.

"Our work shows that the remarkable synchronization of behavior across such vast distances is linked to the North Atlantic Oscillation," Liverpool ecologist Andrew Hacket-Pain said in a news release. "We think this is because a strong NAO synchronizes climate across large parts of Europe, especially during key phases of the tree reproduction cycle. This helps to synchronize seed crops across such large areas, but future work will be required to firmly establish this mechanism."

Scientists published their work on the subject this week in the journal Nature Communications.

Researchers say the correlation between masting and the North Atlantic Oscillation was weaker during the first half of the 20th century than it was during the last 60 years. They hope more detailed analysis will help them better understand how the two phenomenons interact. The relationship between the two phenomena could explain a variety of other ecological patterns.

"The synchronization of seed production is important, as it has knock-on effects on forest ecosystems," Hacket-Pain said. "For example, heavy seed crops increase food availability for woodland-based birds and small animals, and consequently tend to increase the size of such animal populations in the short-term. Additionally, it has implications for human health, as the increase in animal hosts has a positive effect on tick numbers."

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