There are a lot of oak berries on the ground in Calaveras woodlands this fall season.
Berries and nuts are other names for “acorns” when it comes to oaks, the only tree or shrub with off-springing fruit not named after the parent. The Old English word aecern was pronounced “'ae-kern.”

Apple trees produce apples; raspberry bushes bear raspberries; pine trees generate pine nuts; hickories make hickory nuts. But oaks, of which there are about 600 species in the world and eight in California, make berries called acorns. And that’s just the beginning of this ecologically mysterious subject in which shadowy oak trees appear to resemble human beings.

“Conventional wisdom is that when plants are more stressed, they tend to put out more seeds,” said Don Urbanus, owner of Rising Sun Nursery in Burson. “So this could mean they’ve been stressed,” he said, groping for an explanation for the cornucopia of acorns this year. “Some people think they can predict the winter weather to come by the number of acorns that fall to the ground, but I’m not really sure.”

“There’s a huge crop this year,” agreed Mick Stockard, who has studied oaks for 50 years and grows them from seed at Calaveras Nursery off Highway 12 east of Valley Springs. “I’ve always heard that saying,” he said of Old-Farmers-Almanac type lore. “It’s an old, old story. A lot of people believe it.”

At Delta Blood Bank in San Andreas recently, people were talking about acorns as they rested the required 15 minutes after giving blood.

“Acorns have been whacking my bus more this year,” said Robin Price, a school bus driver and horse owner. Price has also noticed her horses eating acorns like they were going out of style. She has had to especially restrain her pony, because she said the high tannin content can kill animals if too many of them are consumed. “They’ve been known to eat themselves to death,” she said of horses. In the 20 years Price has lived in San Andreas, off Pool Station Road, this year, she said, has been only the second or third fall season when she has noticed such a large crop.

To oak specialists, the phenomenon is known as a “mast year,” when oaks are “masting,” as if raising a sail up a ship’s mast to catch the wind. But the word actually derives from more humble origins as a nutmeat, or food (mast) source, for foraging animals.

Price said it seemed to her that in years past a rainy winter followed a mast season. “It seems like it was a lot of rain,” she said, remembering. “It was a more rainy winter than usual.”

Nature’s economy

“It may have to do with the reproductive cycle and when they come into a lot of stress,” said Stockard, echoing the hypothesis of Urbanus. “We had a dry winter last year,” he said. “The oaks may have thought they were coming to the end of the world, so they produced more acorns than usual to ensure their reproduction.

“Ninety-nine percent of a nut is stored nutrients,” he said. “An acorn is a little package of nutrients with a little embryo inside to start the tree off. Sometimes oaks produce a small crop, sometimes a big crop, sometimes no crop at all.

“It has absolutely nothing to do with the future (winter),” Stockard said. “It’s the past spring.” Following a wet winter or spring, the oaks may “reason” that they don’t have to work so hard to provide a new generation of saplings, because things have been going pretty well in their environment: They kick back, putting their energy into personal growth.

But if rainfall is scanty, or the season drier and warmer than usual, they may get worried about their species’ future well-being. They face a propagation challenge, with 15 percent of canopy blue oaks dying each year under normal conditions of mortality: storms, disease and old age.

Then there’s temperature. A dry, warm spring is more conducive to conveying oak pollen through the air to other oak flowers in the vicinity.

“A wet spring means they can reduce pollination,” said Stockard. “The real reason oaks have heavy acorns this year is pollination,” he said. “Oaks are wind-pollinated. A dry spring means they can freely pollinate the female flowers. Most are one-year oaks, but some are on a two-season cycle,” meaning they are reacting to weather and metabolic conditions from two years earlier.

According to the Hastings Reservation, a biological field station of the University of California, Berkeley, a pollinated oak flower matures to produce a “nubbin,” which grows into an elongated ovary with a cap-an acorn. Dropping to the ground when ripe in late summer, the acorn is still a long way from making good on its oak-freighted promise. “The chances of one acorn making it to become an oak tree are very slim-less than 1/10,000,” according to Hastings’ Web site. “That means that for every 10,000 acorns, only one will become a tree!”

Hastings’ Walt Koenig and Johannes M.H. Knops, in a paper published in the journal American Scientist, concluded that masting is an evolutionary adaptation of oaks to some environmental challenge-principally, having their seeds eaten by predators. The chances of reproductive success are vastly improved if an overwhelming number of acorns are produced, “because each seed has a higher probability of escaping predation.”

Individual oaks do not mast. Masting is a group phenomenon, resulting when a population of trees synchronize their reproductive activity. In a mast year, a single mature blue oak can produce more than 100,000 acorns, more than 10 times the annual average, but is likely to produce few or no acorns in a poor year, according to Koenig and Knops.

“Trees must synchronize the quantity and timing of seed production,” the scientists say. “In this way, by mechanisms that remain poorly understood, the masting trees apparently come to a consensus as to how bountiful a crop to produce in a particular year.”

During mast seasons like this fall, oak tress put their individual growth on hold. Scientists have confirmed this using dendrometers to gather precise measurements of trees’ radial growth at the trunk level during successive years of their lifecycle. They shunt most of their resources into flower and seed production during mast years, while shifting them back into growth during poor acorn-crop years.

“The trees just can’t do that (produce bumper crops) year in and year out,” Stockard said. “They just can’t sustain that level of production. It’s a tremendous stress load on the tree to produce all those nutrients and stuff them all in those little acorns.”

Valley oaks and blue oaks are two of California’s most common species, both requiring a single year to mature acorns-providing that warm, dry conditions prevailed the prior spring. Other species of oak require two years to mature acorns. Since 1994, Koenig has conducted surveys at 14 localities in the state, including the foothills, the results of which suggest that synchrony in several species is widespread. In the case of blue oaks, one of the most extensively distributed trees in California-about 5 percent of the state’s total land area-during spring pollination the oaks manage to keep in sync with one another throughout their ambit-both the Coastal and the Sierra Nevada ranges in their entirety.

Theories, effects, hypotheses

With an estimated population of between 100 and 200 million trees, blue oaks are strongly synchronous in initiating their reproductive cycle. Eleven years of data collecting has shown that trees as far apart as 600 miles and more coordinate their asexual activities in synchrony with other blue oaks.

A chemical signal is thought by some scientists to be the command mechanism by which the process works, with molecules wafting through the air from one tree to the next, stimulating the females to flower and the males to produce pollen-and to produce them both in mass quantities during scheduled mast years. Nutrients passing through the root-fungus systems of the trees is another theory.

But both these theories are insufficient to account for trees not in the relatively close proximity of others. The so-called “resource tracking hypothesis,” by itself, will not do; there’s more to it than rainfall and temperature acting as triggering agents. Both external, weather-related causes and internal, metabolic causes have roles to play in explaining the mystery of oak reproduction.

The Gaia Hypothesis, first proposed by British biochemist and NASA space program director James Lovelock in 1970-that the Earth's biosphere, named after the Greek goddess Gaia (“Earth Mother”), acts like a self-organizing system, working to keep its parts in a kind of equilibrium conducive to life-seems to offer a helpful answer. Some Gaia Hypothesis proponents claim that the Earth’s biosphere is consciously manipulating the climate in order to make environmental conditions more livable. Lovelock’s collaborator of 25 years, American microbiologist Lynn Margulis, contends that symbiosis, not chance mutation, is the driving force behind evolution. Margulis, an expert on the role that microorganisms play in evolution, believes that cooperation between organisms and the environment are the chief agents of natural selection-not competition among individuals.

The El Nino weather phenomenon of recent years is an example of an extreme anomaly in climatic conditions explained by “the Moran effect,” named after an Australian statistician in the 1950s who did research on how weather can affect separated populations of trees and birds to synchronize their population cycles across large areas. Unusually warm temperatures attributed to El Nino at the equator in the Pacific Ocean have been said to have created changes affecting the direction of ocean currents, rainfall and air temperatures across large portions of the globe.

Synchrony in the reproductive cycles of the trees has also been associated with the Moran effect. In the case of California blue oaks, preliminary evidence suggests the trees use fluctuations in spring temperatures as their cue for whether to invest resources in growth or reproduction for any particular year. The occasional result, says Koenig, is “geographic synchrony of masting in this species-a Moran effect.” Warm, dry conditions during oak flowering seems to be the triggering mechanism and synchronizing agent in mast fruiting. In several oak species, including the blue and valley oaks in California and the white oak in eastern North America, this appears to be what occurs.

Predicting how El Nino’s climate change will affect acorn masting is one of the challenges scientists face in accounting for the boom-and-bust cycle of seeds made available for predators-what scientists call “trophic cascades,” the rippling effects of the acorns’ availability in the food chain of predators. Interactions between species of insects, rodents and larger mammals that eat acorns ripple through the food chain, altering populations. Deer, mice and tick populations feast during mast years, causing populations to explode and raising the incidence of tick-borne Lyme disease.

California’s oaks have fallen on hard times of late. The state’s oak woodlands include some of the largest remaining old-growth forests in the nation, but they remain relatively unprotected, with more than 80 percent in private hands. Some 24,700 acres of oak woodland are estimated lost each year in California to development or cleared for rangeland. An acre in the Sierra Nevada supports an average of 45 oak trees, according to the California Oak Foundation. The result is that an insufficient number of oaks are left behind, often failing to allow for effective pollination and species reproduction. The wind-driven microscopic pollen may never reach them; isolated stands of oaks may be too far away for regeneration to take place.

Valley, blue and Engelmann oaks are three species believed to be critically affected by inadequate regeneration of their numbers throughout much if not all of their range. In the Sierra foothills and at higher elevations within Calaveras and Tuolumne counties, valley and blue oaks, along with some others-black oak, tanbark oak, tanoak, inland scrub oak, white oak and canyon oak (or gold cup live oak)-are predominant.

The other more recent threat to oaks is from a tree disease, sudden oak death, or SOD. First detected in 1995, the fungus-caused disease, together with the oaks’ poor record of regeneration, threaten at least five of the state’s eight species, and virtually all oak habitats in California, according to studies.

What ultimately is the meaning of our acorn boom? The answer, my friend, was blowin’ in the wind...last spring.

Contact Phillip Gomez at pgomez@calaverasenterprise.com.