Scientists and squirrels alike are wondering where the acorns went in 2008. In Connecticut the chestnut oaks, Quercus prinus, produced a good crop of acorns, but most other oak species were barren. Some people found no acorns at all, or much smaller acorns than usual. While the Washington Post (Nov 29, 2008) described a total absence of acorns in the DC area and squirrels were eating pumpkins, the Newburyport Daily News (Dec 4, 2008) noted highly sporadic cropping: high on Cape Cod, in Providence, and western Massachusetts; but low or absent in much of the rest of Massachusetts, Connecticut, and New England. Missouri and Alabama conservationists found 2008's white oak acorn crop between 120 and 190% above the average, but the red oak acorn crop was only 9 to 68% of the average. The Sierra Sun of California (Nov 26, 2008) , marveled that firs and oaks were producing enormous numbers of seeds. This phenomenon is part of a plant strategy known as mast cropping.
What is a Mast Crop?
A mast crop is both a primary food for many organisms and fluctuates in availability from year to year. Graph 1 (Picture 2, adapted from "Evolutionary Ecology of Masting Trees"), shows that many tree species follow a coordinated boom or bust cycle where most trees bear an abundance of fruit in some years and almost none in others. The fruit of these trees forms a significant portion of the food for insects, large birds, and mammals.
The Recent History of Acorn Masting in the US
Although most locations in the US are finding a scarcity of acorns for 2008, Sacramento, CA is experiencing the heaviest acorn crop ever recorded there.
Table 1 (Picture 3) shows the locations and intensity of seed production during several recent years of acorn production. Most trees are only able to produce heavy crops one year at a time. Different oaks vary in the timing of boom years:
- Black oak (Q. velutina) have an approximately two year cycle.
- White oak (Q. alba), have a three year cycle.
- Red oak (Q. rubra), have a four year cycle.
The timing of these cycles is not precise. They will sometimes take more or less time than indicated. Although most years have a moderate crop, in a few years most species might produce an abundance of seeds, while in other years very few will and the mast crop will fail to feed the consumers that depend on the seeds.
Since most species of seed predators specialize on a certain type of seed, the population of a maple predator can increase in a year of low acorn output if there had been an abundance of maple seeds that year. The maple predators will not affect acorns if the oaks produce a bumper crop of acorns when the maple predator population is high. The same holds true for acorn predators and maples. Of course, some seed predators (such as the Gray Squirrel, Sciurus carolinensis) are opportunists and not reliant on a single source of food.
Local Effects of a Bumper Acorn Crop
Carl Stamm, a retired wildlife manager, found in Connecticut, after a heavy acorn crop in the fall of 2007, turkeys, Meliagris galloparvus, and white-tailed deer, Oedocilus virginianus, were absent from gardens during the subsequent winter. Little wonder. They stayed in the woods feeding on acorns. Even though acorns were eaten in abundance, many were still on the ground in January. Unless they lived near chestnut oaks during the fall of 2008, southeastern Connecticut gray squirrels were scurrying around scrounging a few nuts here and there for storage.
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