NSRC RESEARCHER PROFILE:  Paul Schaberg
Finding connections among acid rain, soil nutrient loss, and tree health in the Northern Forest.

Video: Tree Health and the Northern Forest

"Healthy forests mean a healthier planet," emphasizes Paul Schaberg, research scientist with the U.S. Forest Service Northern Research Station in South Burlington, Vermont. "The Northern Forest provides valuable ecosystem services, including wood products, carbon sequestration, bioenergy, nutrient cycling, gas exchange, and food and medical products, upon which all life and human societies rely."

As a tree physiologist, Paul has spent more than twenty years studying impacts of anthropogenic, or human-associated, stress (air pollution, acid rain, climate change) on tree physiology and forest health to help preserve the ecosystem services the forest provides. His most recent research examines connections between acid rain-induced soil nutrient loss and forest tree decline in the Northern Forest.

"My research has concentrated on the decline of forest trees in relation to calcium depletion, or loss, from forest soils," explains Paul. "Calcium is a critical nutrient that helps plant cells respond to stress. Uptake of soil calcium by tree roots is inhibited when acid rain leaches calcium from soils and makes aluminum—which is potentially toxic to plants—more available."

Beginning in the late 1980s, Paul and his colleagues at the University of Vermont, including Gary Hawley, Donald DeHayes, and several graduate students, climbed to the forefront in demonstrating acid rain's impact on high elevation red spruce throughout the Northeast. Since then, with Northeastern States Research Cooperative (NSRC) funding, they have studied impacts of calcium depletion on red spruce and its susceptibility to winter injury on calcium-fertilized and unfertilized plots at Hubbard Brook Experimental Forest in New Hampshire.

"Limited calcium availability increases the likelihood for freeze-induced mortality of spruce needles especially at higher elevations," explains Paul. The researchers found that needles from trees growing on calcium-fertilized soils stored greater amounts of carbohydrates, exhibited greater antioxidant activity, and were dramatically more cold tolerant than needles from spruces growing on calcium-depleted soils.

"Paul brought the best science together on the impacts of acid rain on cold tolerance of red spruce when I requested his written response to public comments on a draft environmental impact statement for New Hampshire and Maine's White Mountain National Forest," acknowledges Stephen Fay, retired forest soil scientist for the National Forest. "I couldn’t have responded appropriately without Paul’s extensive scientific knowledge and research experience on acid rain and forest health. The willingness of Paul and other scientists to step up to bat on very short notice helped to significantly strengthen the environmental analysis during preparation of the final environmental impact statement and positively impacted land management plans for the Forest."

Another forest tree species affected by acid rain and calcium depletion is sugar maple. Paul and his university colleagues, along with scientists Scott Bailey and Christopher Eagar from the Northern Research Station in New Hampshire, completed two NSRC-funded projects that investigated effects of calcium deficiency on sugar maple decline. The researchers worked in hardwood stands, representing a range in calcium availability, throughout Vermont and at Hubbard Brook to explore relationships between site nutrition and sugar maple health and stress response. (NSRC Project Links: Calcium Deficiency Implicated in Sugar Maple Decline and Adding Calcium to Forest Soils Improves Growth, Health, and Wound Healing of Sugar Maple)

"We found that healthier stands had higher levels of soil calcium. Average annual tree growth over the decade prior to testing was greater for trees in stands with high foliar (leaf) calcium content and low foliar aluminum," says Paul. "Maples on plots that had been fertilized with calcium had better tree crown health and improved wound healing compared to trees on aluminum-fertilized plots and unfertilized plots."

Paul and Gary are currently at work on two more NSRC projects to assess connections between calcium depletion and shoot (branch tip) freezing injury in sugar maple and to study calcium depletion as a limitation to tree growth and carbon sequestration (storage) in sugar maple and American beech.

"Calcium is an important component of woody cell walls and is involved in plant photosynthesis, respiration, and formation and breakdown of carbohydrates," explains Paul. "Tree calcium deficiencies could impede woody growth and leaf formation by reducing structural carbon gains and altering spring sugar levels—the basis for the maple syrup industry—while otherwise disrupting carbon sequestration that helps offset carbon dioxide in the atmosphere."

While Paul is working to maintain the health of existing tree species in the Northern Forest, he is also concentrating on restoring those we have lost, such as the American chestnut. This tree species was wiped out by a deadly fungus introduced to the United States about 100 years ago. With NSRC-funding, Paul and Gary are identifying seed sources of chestnut that exhibit greater cold tolerance for survival in the North and testing the influence of different tree canopy conditions on growth, cold tolerance, and winter injury of chestnut seedlings.

As an adjunct associate professor at the University of Vermont, Paul has advised many graduate students who work on his research projects. He co-teaches a course on human health and the environment with his wife Patricia O’Brien, MD. Paul has hiked and skied throughout Europe and the western United States, but he has a special connection to the woods of the Northern Forest region.

Video produced by the Northeastern States Research Cooperative and the Northern Forest Center

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© 2010 NORTHEASTERN STATES RESEARCH COOPERATIVE
Funding for this website provided by the USDA Forest Service, an equal opportunity provider. Partners include:
The Rubenstein School of Environment and Natural Resources at the University of Vermont
University of New Hampshire in cooperation with the Hubbard Brook Research Foundation
Center for Research on Sustainable Forests at the University of Maine
State University of New York College of Environmental Science and Forestry