Soil Type and Forest Vegetation Influences on Forest Floor Nitrogen Dynamics at the Bear Brook Watershed in Maine (BBWM)

The paired watershed experiment at the Bear Brook Watershed in Maine (BBWM) provided an opportunity to study changes in forest soil O horizon properties as a result of experimental, chronic N additions. The West Bear Brook watershed received elevated N and S inputs since November 1989 as bimonthly applications of (NH₄)₂SO₄. Forest floor samples (O horizon) were collected in July of 1992 from three dominant stand and five soil types at BBWM. The (NH₄)₂SO₄ amendments in the treated watershed (West Bear) stimulated potential net nitrification, but significant increases were found only in hardwood O horizons after three years of treatment. Hardwood stand forest floor soil materials had the lowest C:N ratios (mean=23), compared with mixedwood (mean=27) and softwood stands (mean=33). NH₄-N accounted for over 95% of the inorganic N in the forest floor. The lack of a strong relationship between soil type and potential net N mineralization at BBWM, coupled with conflicting results in the literature, suggested that stand characteristics were more important than conventional soil nomenclature based on pedogenetic features, or 2.5 years of treatments, in defining differences in soil N dynamics and responses to increased N inputs.