No one has yet been able to predict which years will be mast years for a given species. The theory is that normal years provide just enough food for a smallish population of animals to survive. In a mast year, such an overabundance of food is available that lots of acorns are left to germinate and grow up. Of course, the quantity of food available also results in larger populations of deer, squirrels, and mice, which have their own impacts. For example, all those extra mice are hard on ground nesting birds and also on gypsy moths, but good for owls and other predators. Life isn't easy, though, and the charitable oaks revert to their stingy ways the next year. No one seems quite sure what triggers all the trees to participate in the mast, as by doing so, they have to allot resources which would otherwise be used for growth.
One of the visible reminders of last year's amazing acorn production is the large number of red oak seedlings scattered throughout the woods. Now that everything is brown and bare, the bright red leaves of the tiny red oaks stand out like little beacons.
A great article on the subject was published in American Scientist magazine in 2005.