University of Vermont

University Communications


Calcium May Supplement Maple Production

By Cheryl Dorschner Article published October 13, 2004

Bright Maple
Calcium promotes strong bones... and trunks? UVM researchers say amending calcium-poor soils may boost maple production. (Photo: Cheryl Dorschner)

As autumn spreads its warm colors across the Northern Forest, nearly all eyes gaze upward.

But scientists studying how to improve the health of the forest focus in the opposite direction, suspecting that soil calcium deficiencies are at the root of widespread problems caused by acid rain.

University scientists are tackling the issue in a new way and will discuss their findings at the International Maple Producers Conference Oct. 17-19 in Lake George, N.Y. Timothy Perkins, a research associate professor of botany, will discuss and offer the first copies of his co-authored booklet, “Fertilizing A Sugarbush,” which recommends that sugarmakers add calcium to their woodlands to increase maple production.

The publication, funded by UVM’s Agricultural Research Station, is the culmination of Perkins and Timothy Wilmot’s seven-year, $285,000 study that ended in 2003 and was funded by the Freeman Foundation.

“If your site is deficient in some nutrient not just calcium — you may be able to fertilize your trees and increase production. However, calcium is the number one deficiency in soils throughout the Northeast,” says Perkins, director of the university’s Proctor Maple Research Center in Underhill.

Perkins recommends that forest owners perform a soil test or look at other plants at the site that indicate whether soil is alkaline or acidic before considering adding amendments. Sugarmaker Arthur Krueger took this advice and when the soil test on a ten-acre stand near the southern Vermont town of Cuttingsville showed an acidic pH of 4.5 (on a scale where 7 is neutral) he decided to experiment. A local business offered him free calcium carbonate, commonly known as lime, and he took 10 tons.

Fertilizing forest no small task
Although it may be a stretch to say that just as humans need calcium for strong bones, trees need calcium for strong trunks, UVM researchers say the effects of calcium deficiency in trees is something like a weakened immune system that makes them vulnerable to a host of stresses such as storms, insects and drought.

Stands of sugar maples, referred to as sugarbush, and forests in general, grow densely and often are without roads in areas where the terrain may be hilly. So the recommendation is not as easy as the more common practices of gardeners liming a lilac bed or farmers fertilizing a cornfield before planting.

Acting on preliminary findings of Perkins’ and Wilmot’s work, Krueger plans to add one ton per acre as time allows and at various times of year. Based on Krueger’s description of this process, it will be no small task.

“In order to get the lime in where the trees are I use a pony, a cart, and a shovel for a couple reasons. One, you do a lot less damage to the roots than you do with a vehicle, and two, I guess I should’ve been born an Amish man,” he says. “It takes three horse hours and five man hours to spread a ton of lime. Already it looks like I’m doing some good — trees are greener, there’s more life and slower decline on the top. But I’m like the story of the little Dutch boy with his finger in the dyke,” he adds. “I can lime a small portion of my woods but the problem is with all the forests.”

Perkins emphasizes that “fertilizing and liming are not panaceas,” adding that if the stand is not thinned or if the soil is already fertile, it won’t help. While adding calcium is intended to aid maple production and not fall color, calcium is the link between the overall health of maple trees and the damage caused by acid rain. Acid rain leaches calcium out of soil and acidic particles and gases landing on leaves and increases the availability of aluminum, which further limits calcium uptake.

“There’s not yet conclusive evidence that there’s a link between acid rain damage and fall leaf coloration,” says Paul Schaberg, a UVM adjunct faculty member and U.S. Forest Service scientist. “Data indicates that calcium is an important trigger in the production of the pigments (anthocyanins) that produce red color in leaves. “But how that plays out in the landscape, we don’t know. We don’t even have the data on it."

The acid rain link
Theoretically, by depleting calcium, acid rain could mute the production of red leaf pigments, according to Schaberg. However, by acting as a stress itself, acid rain could also temporarily trigger greater stress response, including red color production. “Whatever happens with leaf color, the more important issue is the influence of calcium depletion on the overall productivity and health of forests. We know that red spruce and sugar maples are especially sensitive to calcium loss, and if we lose them it affects the whole ecosystem.”

Speaking as a member of the UVM research team of Don DeHayes and Gary Hawley, Schaberg says the team suspects that red spruce and sugar maples may be the “canaries in the coal mine,” early indicators of problems that will affect many tree species.

Just as gardeners amend some soils with limestone to bring the pH closer to neutral, some wildlife managers add lime to stream water to reduce acidity and restore fish production. Likewise researchers experimented with adding calcium to soils in a section of forest at the Hubbard Brook Experimental Forest in Durham, N.H., in 2003 with positive results.

However Schaberg is quick to point out that this exercise “cost a million dollars for one watershed on one side of one mountain."

“Growing evidence indicates that at least some forests benefit from calcium addition to replace the calcium lost by acid rain. However, this raises an important question — what is the most cost-effective method of combating acid rain-induced calcium loss?,” he says. “It would be an extremely expensive, Herculean chore to add calcium back to all the forests that are being depleted by acid rain."

Or as sugarmaker Arthur Krueger aptly puts it, “an ounce of prevention is worth 10 tons of lime.”