Can adding calcium help forests?

New Hampshire forest in the "spring" — New Hampshire forest in the “spring”

Title: Restoring Soil Calcium Reverses Forest Decline

Authors: John J. Battles *†, Timothy J. Fahey ‡, Charles T. Driscoll , Jr.§, Joel D. Blum , and Chris E. Johnson §

Journal: Environmental Science & Technology Letters

Affiliation: † Department of Environmental Science, Policy, and Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, California 94720, United States ‡ Department of Natural Resources, Cornell University, G16 Fernow Hall, Ithaca, New York 14853, United States § Department of Civil and Environmental Engineering,Syracuse University, 151 Link Hall, Syracuse, New York 13244, United States Department of Earth and Environmental Sciences,University of Michigan, 1100 North University Avenue, Ann Arbor, Michigan 48109, United States

Background

Acid deposition, commonly referred to as acid rain, primarily results from the burning of fossil fuels and has been plaguing industrialized regions for decades. It can acidify soil and water, thereby damaging plants and aquatic animals. In the last few decades, governmental regulations primarily in North America and Europe have curbed the occurrence of acid rain in these areas. But some effects have lingered – in particular acid deposition led to a huge decrease in the amount of certain nutrients in soil, including calcium. This persistent depletion hurts forests. These effects are magnified in areas that have not started to regulate pollutants that cause acid rain.

In this paper, the authors report on a fifteen year field study where they examined the effects of calcium depletion due to acid deposition. Many studies have indicated a connection between forest decline and acid deposition, but it is a tricky problem to address because of the numerous stresses placed on trees in their natural habitats.

Experimental Procedure

The authors conducted their experiments at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire where two of the primary tree species are sugar maple and red spruce, both of which are known to be very sensitive to calcium levels. The authors hypothesized that depleted calcium levels could be causing some of the forest decline at HBEF.

In order to test their hypothesis, the authors added calcium silicate to a watershed and compared the forest growth to a control watershed. Starting in October of 1999, wollastonite (CaSiO₃) was added to the experiment site via helicopter. (I wish more of my experiments in grad school involved flying helicopters over forests in New Hampshire).

In order to estimate the amount of tree present in both the experimental watershed and control watershed, the authors made estimates of the biomass (amount of biological stuff) by measuring the volume of tree bole (basically tree trunks) and leaf sizes.

Results

On the experimental watershed, the decline in biomass began to reverse in 2001, with an especially large growth in biomass from 2006 to 2011. This gain in biomass did not occur in the control group and, in fact, tree biomass in 2012 was still lower than that observed in 1997.

Comparison of tree biomass overtime in the experimental and control watersheds

Conclusion

The results strongly suggest a connection between soil calcium levels and forest growth. The authors determined that sugar maples were the most affected by the increase in soil calcium with a large percentage of the overall increase in biomass due to the increase in sugar maple biomass.

This study further supports a connection between acid deposition and forest decline. The authors state, “Continued vigilance in the control of acid rain precursors will be needed to correct these problems, and aggressive options to reduce pollution in rapidly industrializing regions of Latin America, Asia, and Africa are warranted.”

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