A 'Mast Year' for Acorns? That's Nuts!

By Kirstie Hettinga, AccuWeather.com Staff Writer
September 21, 2010, 2:30:15 PM EDT

People with oak trees in their yards may be getting the impression that there is a little extra crunch under their feet this year.

The reason for a bumper crop of acorns, also known as a "mast year" may have a tie to weather.

Dr. Marc Abrams, a professor of forestry at Penn State, said mast years occur when nut-producing trees such as a oaks "produce an overabundance of nuts in a particular year, maybe five or 10 times more than an average year."

However, Abrams described the mast year phenomenon as "one of the amazing mysteries in nature that we still do not have a handle on."

Mast years happen irregularly, which Abrams said can make it challenging for scientists to understand what causes a mast year.

According to Abrams, a mast year can occur twice in a row or they might be several years in between.

"There's no way to predict it," he said.

While there is some speculation that mast years have a weather connection, Abrams said that there is no definitive research in the area.

"There might be, sometimes, a weather connection," he said.

Determining when a mast year occurs and what causes it is further complicated by the fact that most of the acorns or nuts are formed in a two-year cycle. This suggests that if there is a weather connection, it could apply to the year before an actual bumper crop.

Mast events also happen over a vast geographic area, which will most likely see a variety of weather conditions within its boundaries. -- as much as hundreds, thousands of miles. And Abrams said within that large a region, the weather can vary significantly.

Beyond weather, Abrams said, "There is a chemical signal hypothesis, that maybe the trees are giving off some sort of chemical cue or signal that cues them to have an abundance."

But he said, "There's other things that could cue trees in a region. One would be a weather condition that they're all tuned into."

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