R. D. Yanaia*, T. G. Siccamab, M.A. Arthurc, C.A. Federerd and A.J. Friedlande aSUNY College of Environmental Science and Forestry Syracuse, NY
bYale School of Forestry and Environmental Studies New Haven,
* Corresponding author. Tel.: +1-315-470-6955; fax: +1-315-470-6954; e-mail: firstname.lastname@example.org
LOSS OF base cations from forest soils can be accelerated by acid rain, by forest regrowth following harvest removals, and by declining inputs of base cations from atmospheric deposition. Calcium losses from forest floors have been reported at several sites in the northeastern US. To test for loss of base cations from forest floors at the Hubbard Brook Experimental Forest in New Hampshire, we analyzed samples collected at seven times between 1976 and 1997. Calcium and magnesium contents of the forest floor did not decline significantly; a change greater than 0.9% per year would have been detectable. Concentrations of Ca were 40% higher in 1969-70 than in the current study, but the difference is partly due to changes in collection methods. Magnesium concentrations were too variable to detect a loss of less than 47% over the 21-year interval. To determine whether base cation losses were associated with forest growth, we resampled a chronosequence of northern hardwood stands in the White Mountains of New Hampshire. The 13 stands did not show consistent changes in Ca, Mg and potassium over the 15-year interval. Losses of these cations were most pronounced in stands logged more than 25 years earlier. Younger stands, contrary to our expectation that rapid forest growth should cause cation depletion, all gained base cations in the forest floor. Early in stand development, these forest floors appeared to accumulate biomass along with living vegetation, rather than serving as a net source of nutrients. Finally, in a regional survey of 28 mature stands in the northeastern US, some lost significant forest floor Ca and Mg between 1980 and 1990, while others gained. The average change in Ca and Mg content was not significant; a loss 1.4% per year would have been detectable. Forest floors in the region are not currently experiencing rapid losses of base cations, though losses may have preceeded the onset of these three studies.
Ca(a) and Mg(b) contents of forest floors in 28 stands in the Northeastern US. Error bars show standard error. Archived samples from 1980 (Johnson et al. 1982; Friedland et al. 1984) and 1990 (Friedland et al. 1992) were analyzed.
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