Acorns: The Forest’s Bread and Butter


Researchers use net traps to study the season’s acorn yield and how it affects the forest. Photo by Julia Kirschman, U.S. Forest Service
Researchers use net traps to study the season’s acorn yield. Photo by Julia Kirschman, U.S. Forest Service

Acorns are often referred to as “a keystone species of the forest” because of the critical role they play in ecosystem dynamics. Rodents feed heavily on acorns and, in turn, predators such as foxes and hawks prey on rodent populations plump from acorn feasting.

Deer and black bears depend on acorns too. In fact, if a pregnant black bear doesn’t consume enough acorns in the fall, her embryo is less likely to fully develop, and even if her cubs are born, she won’t be able to make enough milk to feed them.

And don’t forget the oaks themselves. “Of course, acorns are the seeds to future oaks,” says U.S. Forest Service Southern Research Station’s Dr. Katie Greenberg. This year, however, her meanderings in the mountains of western North Carolina have less of a crunch than in years past.

“Around here, acorn production seems to be low,” says Greenberg, who adds that, for oak species, “this year appears to be a pretty bad year for everything.”  According to biologist Gary Norman of Virginia’s Department of Game and Inland Fisheries, “Virginia is also experiencing a significant mast failure” and West Virginia “reported their mast index was the lowest they’ve recorded in the survey history.”

Similar to the West Virginia surveys, Norman’s research at Virginia study sites shows that this year’s acorn production in both white and red oak species is the lowest it has been in the last six years. This fall, acorns covered only 5 percent of white oak tree tops, while red oaks boasted a slightly higher count at 8 percent. In 2012, the same surveys showed 58 percent tree top coverage in white oaks and 65 percent in red oaks, dwarfing this fall’s numbers.

So what’s the deal with these oaks? Were their heads in a cloud during reproductive season? Not exactly, though clouds might have held some influence. “This year the acorn shortage could be because we’ve had so much rain in the spring and in the summer,” says Greenberg.

The problem with too much rain is that it makes pollen soppy, and wet pollen stubbornly resists being blown by the wind — a step necessary to pollinate other oaks. Drought conditions and late spring freezes can kill oak flowers and inhibit acorn production as well. But in the end, “there’s a mystery element with oak trees,” says Greenberg. Though the weather is likely a player in this year’s low acorn crop, Greenberg notes that acorn production tends to be erratic. Norman’s surveys bear witness to this notion. Virginia’s white oak species produced low acorn mast in 2007-2009 and 2011, but had significantly better masts in 2010 and 2012.

Read a recent article by Greenberg et al on forecasting long-term acorn production.

Acorn production prediction models for five common oak species in the East.

For more information, email Katie Greenberg at

Access the full text of the article in The Appalachian Voice.

Access the latest publications by SRS scientists.


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