Masting is the simultaneous and dramatic increase in the annual production of seed by large numbers of plants at once….a sort of temporal and spacial reproductive coordination. This seems simple enough but the phenomena is really not fully understood. It crosses both species and continents. A good example for North America is acorns. 2006 has been a huge year for oak masting here. Production is so high this year that forest floors and suburban lots are literally blanketed in acorns. In other years one might only see a few and they will almost always be at least partially eaten.
One popular theory about masting speculates that the overproduction of seed super satiates the animal population that feed on them. In the case of acorns there are only so many squirrels (and mice and chipmunks) that can hold only so much acorn in their little bellies over the course of the winter. In addition acorn weevils are also lower in population than the number of acorns available for predation. Even after the mammal and insect predators are full plenty of acorns are left to germinate. So many in fact that in the years to come oak seedlings will often win out and gain a foothold in the race to reach for the sun.
Meanwhile back in the squirrel nest, Momma is happily reproducing at a greater than usual rate. But when the cache of acorns is gone and the remaining acorns have germinated, rending them unsuitable as squirrel food the larger squirrel population will fall back on their opportunistic feeding behaviors. In the years following a masting year acorn production will be low and the squirrel population will diminish more and more….making it more likely that in subsequent masting years the acorn eaters will be at a population low point. This gives the home field advantage to the oaks again and so the cycle repeats.
In the years that acorn feeding rodent populations are low predation on birds may increase. Predatory birds like hawks and owls may hunt more birds since fewer small mammals are available. Even the the rodents may rob nests of eggs and young in larger numbers since their preferred food (acorns) is not abundant.
Not all the publications I read subscribe to the satiation/starvation theory. Another theory is that some years conditions simply favor pollination success more, most notably by wind pattern variations. Still another theory is that the resources (sun, rain, nitrogen) needed by the plant to produce seed vary year to year.
Basically we know masting happens but we don't know for sure why. I have a bowl full of acorns on my foyer table in honor of the occasion this year. I don't think the squirrels will miss them.