COMPARISON OF SOIL GEOCHEMISTRY BENEATH HEMLOCK AND BLACK BIRCH FOREST, WESTERN MASSACHUSETTS, USA
We measured soil pH, exchangeable acidity, exchangeable base cations, and nitrogen mineralization rates over an 80 day period of the 2010 growing season using field incubated soil cores placed in hemlock and younger black birch stands. Although soil pH of organic horizons between hemlock (4.3) and black birch (3.8) are both acidic, the concentration of exchangeable base cations in the organic horizon beneath black birch (3.37 meq 100 g-1 soil) is higher than for hemlock (1.9 meq 100 g-1 soil). Likewise, the base saturation is 10% greater for black birch (34% versus 24%). These results suggest that the acidity typically associated with soils that support hemlock forests has not been neutralized by black birch regrowth. However, more base cations are becoming available within the cation exchange pool. The soil acidity may be stabilized by exchangeable Al3+ , which is similar for the two plots (4.9 meq 100 g-1 soil), whereas the differences in base saturation may reflect variation in inputs of base cations from throughfall and leaf litter. Nitrate concentrations for soils collected from initial cores are significantly higher in the black birch regrowth stand than in hemlock. Nitrogen mineralization rates over the 80 day incubation period will be presented.