PARENT SESSION
Oral Session #35: Nitrogen cycling: Response to inputs, variation in time and space. Presiding: M. Fenn.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
Ecosystem changes in a red spruce forest following 12 years of chronic, low dose, nitrogen addition.
McNulty, Steven 1,2, Boggs, Johnny1, Aber, John 3, 1 2 3
ABSTRACT- During the mid 1980's, there was concern about the potential impacts of acidic deposition on New England forest health. To address this question, four sets of paired nitrogen addition plots (and one set of paired control plots) were established in the red spruce zone of Mt. Ascutney Vermont in 1988. Each year since 1988, 15 to 30 kg N ha-1 year-1 were added to the treatment plots. Since 1988, extensive ecological changes have occurred on the treatment plots, compared to control plots. Foliar nitrogen concentration has almost doubled, nitrogen mineralization potential and living basal was reduced by almost 50%, and dead basal area increased by over 400%. These (and additional) results strongly suggest that low, chronic nitrogen applications can negatively impact spruce health. However, some results have been unexpected. For example, there has been little change in foliar lignin concentration, no seedling regeneration in the gap openings caused by spruce mortality, and forest floor nitrogen concentration has increase on all plots (including controls). To assure that no cross nitrogen fertilizer contamination was occurring on the control plots, in July 2000, we compared control and treatment plot foliar and soils data to five new control plots that we established within 50 m of the current site. Both the results of the long-term nitrogen additions and the new nitrogen saturation drift measurements will be presented.
KEY WORDS: nitrogen saturation, Picea rubens, Mt. Ascutney Vermont