Forgetful gardeners
Many squirrels bury food in autumn, one nut or acorn at a time in hundreds or thousands of little holes. This is called scatter hoarding. They find many again by memory and smell. The ones they never dig up can sprout, so squirrels, along with jays and other animals, plant oak woods without meaning to.
Two families of acorns
Oaks in the white oak group drop acorns that sprout soon after they fall, in autumn. Squirrels tend to eat these straight away. Grey squirrels have been seen biting off the tip where the sprout starts before burying one. Oaks in the red oak group make bitterer acorns that sleep through the winter and sprout in spring, so they keep, and squirrels bury them. In the game, a white-group acorn you bury will have sprouted by winter.
Acorns as people food
People have eaten acorns for thousands of years: the Jōmon people of Japan, many California nations, including the Coast Miwok, Korean cooks making dotorimuk jelly, and Mediterranean families roasting sweet holm-oak acorns. Most acorns are bitter with tannins, so people soak or boil them first. Please don't eat raw acorns.
Sources
- Smallwood, Steele & Faeth (2001), on why squirrels cache red oak acorns: American Zoologist
- McEuen & Steele (2005), squirrels notching white oak acorns: American Midland Naturalist
- National Wildlife Federation: How squirrels hide nuts (pretend burying)
- Bay Nature: Squirrels of California
- USDA plant guide: Tanoak
- Wyoming Wildlife: Red squirrel middens
- Wikipedia: Daimyo oak (dotori and dotorimuk)