My oak tree produced just a few acorns this year. Why?

FAQ
Question: 

My oak tree produced just a few acorns this year. Why?

Answer: 

It’s common for the acorn crop on oak trees to vary from year to year. Most oak species produce a good crop of acorns once every two or three years.  However, the white oak tends to produce a good acorn crop once every four to six years.

Weather and other factors can affect flowering and fruiting. For example, freezing temperatures in spring (when trees are flowering) can damage or destroy the flowers, drastically reducing the fruit crop.