WHY DO OAKS HAVE MAST YEARS? The phenomenon of mast years, with “prodigious” amounts of acorns, has been known for a long time. This wikipedia entry says that the word “‘mast’ comes from the old English word “mæst”, meaning the nuts of forest trees that have accumulated on the ground, especially those used as food for fattening domestic pigs.” (the pigs would be turned loose in the forest). Yet, according to this article on the natureworld/news site by Katrina Rossos: “The true reason for this phenomenon has baffled scientists for hundreds of years.” Scientists are not yet able to predict the occurrence of mast years from environmental factors such as rainfall or temperature. For some unknown reason, all of the oak trees in a region will dramatically overproduce acorns.
Although unpredictable, mast years are theorized to provide an evolutionary advantage for the oak trees. For a period, the number of what are referred to as “predators”—that is, chipmunks and squirrels as well as pigs—will not keep pace with the number of acorns, and more acorns survive to become oak trees.