Disturbing ... but not quite as disturbing as Bruce's pic!
Seriously, we are trashing this planet and it wouldn't surprise me if this is an unexpected result of something we have done. But on the other hand, I noticed that the article said last year was a bumper year for acorns. That means lots more squirrels. That means that this year, assuming a below-average-but-within-normal-range crop, all the acorns would be promptly consumed by the over-populated squirrels, creating the appearance of none at all. I hope it is something natural and self-correcting like that.