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AAAS SCIENCE MAGAZINE, November 26, 2021, reports that “Researchers Probe Climate as a Cause of Banner Nut Years.” The magazine’s Elizabeth Pennisi writes, “New database could help solve the mystery of tree “masting.” 

Here are tidbits about this article, together with my usual Internet sleuthing.

“Tree “Masting.” Britannica defines masting, or mast seeding, as “the production of many seeds by a plant every two or more years of the same species…. Mast seeding is an effective defense because seed predators become sated before all the seeds have been consumed.”

Elizabeth Pennisi notes in Science, “This is a mast year, in which tree species reproduce prolifically and in sync, creating a bounty that will reverberate through the ecosystem for years.”

Ecosystem Responses. Responses occur throughout the ecosystem, as described by Pennisi: “In some years, beech and spruce mast together throughout Europe. The seeds—up to 500 per square meter from beeches—dump enough organic matter to effectively double the nitrogen in the ground, fueling fungal and microbial growth. Rodent densities soar, followed within 1 year by rising numbers of predators like foxes and owls.”

How Do Trees Know When to Mast? “It’s not that trees have crystal balls,” Pennisi says. “Instead, researchers suggest trees are alert to large-scale, long-term climate patterns, which can cause, for example, wet weather one month and dry weather months or a year later.”

This and the following image from Science, November 26, 2021.

Data Collection. Pennisi cites MASTREE, “a database of some 17,000 records, some going back centuries, of nut production in beeches and cone production in Norway spruce…” Also, Mastree+ is a new database being assembled with 65,000 records on 715 species across 63 countries.  

Environmental Prediction. Pennisi writes, “Now, inspired by the potential of a large database that will be published early next year, a group of researchers has explored this idea, called the environment prediction hypothesis, in several papers appearing in the 1 December issue of the Philosophical Transactions of the Royal Society.” 

If climate swings prove to be as important as this hypothesis suggests, researchers say we could have a large-scale “pace-maker” of global forest ecosystem dynamics.

ENSO and Forest Fires. “In North America,” Pennisi says, “conditions fostered by the El Niño-Southern Oscillation (ENSO) can promote both masting in white spruce and forest fires, which open up space for seedlings to grow.”

See “Light My Fire—Selectively” here at SimanaitisSays for details on the importance of this ecological influence. 

NAO Flip-flops. Researchers, Pennisi says, “found masting events in beeches coincided with climate patterns produced by the North Atlantic Oscillation (NAO), in which high and low air pressure flip-flops between the eastern United States and Europe.”

European beech masting, as related to Europe’s NAO phases.

A positive phase NAO+ brings warm, wet winters and dry springs to Europe. A negative phase NAO–, just the opposite. Researchers suggest this decadal trend in masting (the graph’s wavy line) is led by this climate oscillation.

Analyses such as this enhance understanding of the interactions of climate change and masting patterns. In the meantime, Pennisi says, “don’t slip on the acorns.” ds

© Dennis Simanaitis,, 2021 


  1. Paul M Everett
    December 10, 2021

    For a delightful story on masting, see the chapter “The Council of Pecans” in Robin Wall Kimmerer’s “Braiding Sweetgrass.”

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