Date of Award
Program or Major
Doctor of Philosophy
John D Aber
From July to August of 1987 and 1988, a regional sampling of spruce-fir forests across New England was conducted. Forest floors and foliage were sampled from 161 sites, in 11 areas from Maine to New York. Potential net N mineralization, nitrification, pH and analysis of total concentration for selected elements were measured on forest floor samples. Foliar lignin, N, cellulose and elemental concentration were determined for red spruce and balsam fir. Using National Atmospheric Deposition Program N deposition data, a isopleth map of New England wet only N deposition was produced. Estimated N deposition was correlated with longitude (R = 0.87, P $<$ 0.001), forest floor nitrification (R = 0.89, P $<$ 0.0001), the fraction of forest floor net N mineralization which nitrified (R = 0.82, P $<$ 0.001), forest floor net potential N mineralization (R = 0.66, P $<$ 0.5), forest floor C:N (R = $-$0.81, P $<$ 0.001), forest floor Mg concentration (R = $-$0.64, P $<$ 0.05), red spruce foliar lignin Concentration (R $-$0.61, P $<$ 0.05), lignin:N (R = $-$0.79, P $<$ 0.01), and red spruce foliar Mg:N (R = $-$0.57, P $<$ 0.05).
The research supported the theory of a nutrient imbalance between foliar N and Mg as a possible cause for forest decline.
The second half of the research established a series of fertilization additions to spruce-fir plots on Mt. Ascutney Vermont. Four paired plots were amended with NH$\sb4$-N and/or NO$\sb3$-N, over the course of three growing seasons. Combined age class red spruce foliar N, lignin, and cellulose chemistry were measured in June, July and August of each year. Litter mass and chemistry were monitored for two years. Forest floor mass, net N mineralization, nitrification, pH, and elemental concentration were measured. Additions of N fertilizer were correlated with increased foliar %N (R$\sp2$ = 0.78, P = 0.0003) and litter %N (R$\sp2$ = 0.73, P = 0.0006), increased net N mineralization (R$\sp2$ = 0.59, P = 0.005), and decreased red spruce foliar lignin:N ratio (R$\sp2$ = 0.49, P = 0.01). No correlations were found between type of fertilizer applied and measured variables. Increases in net N mineralization stabilized or decreased during the second year of N applications, suggesting a limitation of available C.
McNulty, Steven George, "Nutrient cycling in New England spruce-fir forests" (1991). Doctoral Dissertations. 1647.