Acorn Production: Hindcast, not a Forecast

By Vickie Frantz, AccuWeather.com Staff Writer

September 28, 2012; 5:24PM,EDT

 

 

 

 

Many people believe a large acorn crop is a predictor of a harsh winter. The truth is, the acorns on the ground today are the prediction of weather conditions two or three years ago.
Bucknell University Professor of Biology Emeritus Warren G. Abrahamson, Ph.D and Executive Director of the Archbold Biological Station (located in Venus, Fla.) James N. Layne, Ph.D worked together on a study of acorn production during the years of 1969-1996 (with the exception of 1991).
The pair observed and recorded the acorn crops of two white oak and three red oak species.
"Jim Layne was really the one who got the project started," said Abrahamson. "He also was the one to make sure the data got collected each year."
The findings of the team may surprise you. In a published report dated September 2003, the research showed that the volume of acorn production each year is partly controlled by external factors like precipitation effecting the acorns during different stages of development during prior years.
Acorn production from bud to completed acorn takes nearly two years for species of the white oak and three years for species of the red/black oak, according to Abrahamson.
In 1989, the oaks in the study were subject to a freeze during the growth cycle. Only one species of oak, the Chapman Oak, was damaged. The damaged trees produced their third highest crop of acorns over the entire 27 year of the study in 1990.
The team reported that they did not experience a complete crop failure of any oak species during the study.
If you've noticed a lot of acorns around your house, Abrahamson who resides in Central Pennsylvania, said the Chestnut Oaks are producing them.
"I have never seen such a large crop in the 30 years I've lived here," he said. "Walking around my property is like walking on marbles."
The rainfall and temperatures in Central Pennsylvania during the springs of 2010-2012 have been favorable for acorn production. The table below list the precipitation and temperature totals for the months of March-May for each of the three years.

Year	Avg. Precip.	Actual Precip.	Percent of Normal	Temp. Percent Above Norm.
2010	10.06	9.02	90	4.9
2011	10.06	16.43	163	1.6
2010	10.06	9.75	97	5.7

If favorable weather conditions for acorns mean a bumper crop two or three years later, the crops of 2013-2015 may bring some of the largest crops yet.
"Weather was a very important factor in the study," said Abrahamson. "The production of acorns definitely is not forecasting but hindcasting the weather."