Date of Award

Spring 1995

Project Type

Dissertation

Program or Major

Natural Resources

Degree Name

Doctor of Philosophy

First Advisor

John D Aber

Abstract

Forest floor biogeochemistry was studied in combined field and modeling research in ecosystems representative of forests of the Northeastern U.S. The field study, conducted at the Harvard Forest, MA, focused on changes to organic and inorganic chemistry of forest-floor leachate under experimentally elevated N inputs meant to simulate effects of acid deposition in the region.

Concentrations of dissolved organic carbon and nitrogen (DOC and DON) increased substantially in N treatments in the first year of the study. I attributed this to an increase in production of soluble organics in the forest floor due to an interaction between increased N availability and lysimeter-installation disturbance. In the second year of the study, DOC and DON appeared unaffected by N amendments in a red pine stand that is exhibiting symptoms of N saturation. Concentrations of soluble organic C and N decreased with N amendment in a northern hardwood stand which is retaining all of the added N. I attributed this effect to a decrease in the solubility of humic substances.

Both stands exhibited pH decreases attendant with preferential retention of NH$\sb4\sp{+}$ over NO$\sb3\sp{-}$ in the O horizon. Base cations in the O horizon appeared to buffer solution pH changes better in the pine stand than in the hardwood stand.

Site-level data from previous studies were used to construct a process model of forest-floor decomposition and N dynamics. After validation through blind predictions, the model was used to simulate forest-floor mass and N capital during recovery from clear-cutting in northern hardwood forests. The model was also applied in 10-ha patches across a heterogeneous landscape to predict patterns of forest floor mass and N capital in the White Mountain National Forest.

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