Squirrels as Foresters

squirrel eatingAn ecologist named Joseph Grinnell way back in 1936 once asked how it was that oak trees could colonize the tops of hills and ridges.  Acorns are too heavy for wind to disperse them, and gravity tends to make them travel downhill rather than up.  He concluded that animals must be responsible for getting acorns to high places.


Many animals use acorns as a valuable winter food source.  Deer, turkey, wild pigs, and bears are heavy users, but an eaten acorn cannot germinate and make a tree.  Some members of the squirrel family such as chipmunks and flying squirrels do store acorns for later consumption, but usually store them in tree cavities and underground burrows where they cannot successfully germinate and survive.  Only tree squirrels, such as our own gray and fox squirrels, store acorns by burying them just under the leaf litter and allowing the seed an opportunity to successfully germinate and locate away from the mother tree.

Squirrels do not hibernate, and so must store large quantities of food to see them through the winter.  Acorns are particularly appealing because they provide a lot of calories and are easier to open than nuts from hickory and walnut.


Not all acorns are the same, and squirrels treat each kind differently.  There are two major groups of oaks: red and white.  Red oak acorns are rich in fats, but contain a lot of tannic acid, which makes them bitter.  White oak acorns are less fatty but have a much lower amount of tannin, thus better tasting.   The two oak groups also differ in how they germinate.  Red oak acorns lie dormant during the winter and sprout the following spring, while white oak acorns usually sprout soon after falling to the ground in autumn.


It is a common misconception that squirrels prefer the better tasting white oak acorns. But according to research, when given a choice, squirrels will take the more high-fat red oak acorns.  They also tend to store more red oak acorns for winter and eat more white oak acorns as soon as they find them in the fall.  This is probably because once a white oak acorn germinates, it loses some of its nutritional value.


Based on this behavior, it appears that squirrels have a lot of influence on the spread of various oak species, especially favoring the dispersal of red oaks.  They unknowingly practice the art of forestry, manipulating the growth and development of oak forests throughout the eastern United States.  Considering the high value of oak wood to humans, we owe them our gratitude.


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