Eat all the walnut treats you can this holiday season. They might not be so plentiful in coming years.

Commercially grown walnut trees (Juglans nigra and Juglans regia) are very particular about their growing conditions and drought or untimely frosts can crack the walnut tree's defenses.

"Walnut is really restricted to sites not too wet or dry. It has an extremely narrow range," said Douglass Jacobs, professor of forestry and natural resources at Purdue University, in a press release.