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Some trees reproduce synchronously over large areas, with widespread ecological effects, but how and why?
This autumn, the vast hardwood forests of North America could be chock full of acorns, a pulse of resources that will cascade through the ecosystem, affecting mice, birds and other wildlife for years to come. Over far-flung areas virtually all the oaks of the same species, and perhaps more than one species, are already gearing up to produce the seed crop of the decade. Or not. In fact, there may be almost no acorns, and a substantial proportion of the wildlife will starve or have to eat something else.
Such highly variable and synchronized reproduction is known as "mast-fruiting" or "masting." The term comes from the Old English word, mæst, for nuts of forest trees that have accumulated on the ground, especially for those used as food for fattening swine. Evolutionarily, a significant selective benefit of masting is "predator satiation." The idea is that large crops satiate seed eaters so that some seeds escape being eaten, particularly in "mast" years with bumper crops. To reinforce this effect, small crops keep seed-predator populations so low that there are too few animals to eat all the seed produced during good years. Thus, a higher proportion of seeds overall ultimately escape predation.
People have witnessed masting since time immemorial; after all, it's pretty obvious when you're tripping over nuts strewn all over the path some years and you find barely one or two in others. In agrarian communities, farmers would have been especially aware of the boom and bust cycle because they fed acorns to livestock. Although records are sparse, historical economic data have been used to infer the size of acorn crops from as far back as the mid-17th century. Only recently, however, have scientists begun to recognize the geographic scope and ecological consequences of masting and attempt to explain how this remarkable phenomenon is achieved. So how do all those millions of trees do it?
In this article, we describe the ecological and economic consequences of masting and discuss what causes seed production to vary so widely. This leads us to review the latest research into proposed mechanisms that govern the synchronous production of seed across wide geographic areas. Finally,...