When Nature Goes Nuts - wildlife nurtured by acorns

National Wildlife, Oct-Nov, 1999 by Les Line

An astonishing array of animals are linked in some surprising ways to the mighty oak and its bounty

More than 200 years ago, seven-year-old Ep-hraim Farrar walked to the front of a schoolroom in Ipswich, New Hampshire, and recited a verse written for him by a townsman, David Eve-rett. History doesn't record whe-ther the lad earned an A for his elocution skills, but both he and Everett gained a measure of immortality because of two lines that can be found in any book of quotations: "Large streams from little fountains flow. Tall oaks from little acorns grow."

True on both counts! But if you spend an autumn afternoon sitting under an oak that sprouted around Ephraim's time and watch a plump gray squirrel bury acorns at the rate of one a minute, while a tom turkey scratches away the coppery leaf litter to cram its crop with dozens of the nuts, a new rhyme might pop to mind: "From tall oaks billions of acorns fall. And creatures wild will eat them all."

Indeed, the acorn crop in an oak forest can reach 700 pounds per acre in a good mast year, when one ancient tree with an immense trunk and a spreading crown could yield 15,000 nuts. Yet by the end of November, most of them will be gone. Packets of energy that are easy to open and digest, acorns are a significant food item for some 150 species of birds and mammals and typically make up at least 25 percent of the diets of black bears, raccoons, gray and fox squirrels, wild turkeys and white-footed mice, to name a few. White-tailed and black-tailed deer, meanwhile, eat oak foliage along with bushels of acorns.

In some cases-notably for tree squirrels, woodland mice, blue jays and acorn woodpeckers in the West-having an ample store of the burnished brown nuts, which range in size from a half-inch to 2-1/2 inches in length, can be critical to overwinter survival. For example, the clown-faced acorn woodpeckers live in family groups as large as a dozen or more birds that stockpile acorns in communal granary trees-one nut to a hole-for use when insects are not available. Each woodpecker generation drills a few hundred new holes in the bark, leaving the tree unharmed; one huge granary in California with 50,000 holes represented 100 years of excavation. But when such stores are depleted, acorn woodpeckers wander away from their territory in search of food. And if the mast shortage is widespread, most of the birds will starve.

In the Pacific Coast states, oaks are second in importance behind pines as a natural source of wildlife food. East of the Rockies, they rank number one. Biologists have linked acorn crop failures-caused by late frost that kills the buds or spring rains that interrupt flower pollination-to poor black bear reproduction and meager antler growth on whitetail bucks.

However, scientists have only begun to understand the complex relationships between acorns, animals and plants in the forest ecosystem. Recent research has shown, for example, that a bumper acorn supply leads to a high risk of getting Lyme disease for people in suburban and rural areas. (The worst areas for Lyme disease are the northeastern, north-central and far western states.) Yet at the same time, an abundance of acorns lessens the likelihood of severe gypsy moth defoliation, which can stress and kill oaks.

Researchers have also learned why tree squirrels discriminate between types of acorns-and how a decision to eat a nut on the spot rather than cache it influences the genetic makeup of an oak forest and the rate at which a particular oak species colonizes new areas. And foresters have made an ominous prediction: Trees of the oak genus have dominated much of the country's deciduous forests for thousands of years and comprise nearly half of our eastern timberlands. But if present trends continue, within a century oaks will be only a minor component of the ecosystem.

The Latin name for the oak genus, Quercus, means "beautiful tree," and the United States is blessed with 58 native oaks that reach at least small-tree size, although in the arid West some species are more commonly found as shrubs. Botanists tell us that our oaks originated in Mexico, evolving from evergreen trees to deciduous trees as they migrated northward into colder climates after the last glaciation. Oak diversity also changes from south to north-from 28 species in Alabama to 8 in Minnesota, for instance. Only 9 kinds of oaks managed toeholds in southern Canada.

Taxonomists divide the North American oaks into two groups: white oaks, which have leaves with rounded lobes, and red oaks with pointed, spine-tipped lobes. But there's a more significant difference: The acorns of white oaks mature in one growing season and are sweet to the taste. (Native Americans taught European settlers how to grind them into flour.) Red oak acorns take two years to mature and are bitter with tannin but contain three times more fat. White oak seeds sprout soon after they fall to the ground. Red oak acorns lie dormant during the winter months and sprout in the spring. All of these factors influence the behavior of squirrels and other small animals at harvesttime, which in turn has had a major impact on the disperal and regeneration of oaks.