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
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.
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.
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.
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.”