From CNN.com: Scientists baffled by mysterious acorn shortage

Up and down the East Coast, residents and naturalists alike have been scratching their heads this autumn over a simple question: Where are all the acorns?

Oak trees have shed their leaves, but the usual carpet of acorns is not crunching underfoot.

In far-flung pockets of northern Virginia, Maryland, Pennsylvania, West Virginia and other states, scientists have found no acorns whatsoever.

This sounds like the beginning of one of those bad science fiction disaster films that you find on the Sci-Fi Channel.  First something innocuous, like no acorns, and then everyone dies of a plague or overrun by giant squirrels. 

Humans have made such a huge impact on the environment that any time something different happens in nature, we always have to look to see if we're somehow the cause of it, from bees dying to trees not producing acorns.