Subalpine forest ecosystem responses to long-term nitrogen loading at Loch Vale Watershed, Colorado, USA

Weinmann, Tim, author
Boot, Claudia, advisor
Baron, Jill, advisor
Rhoades, Charles, committee member
Covino, Tim, committee member
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This thesis presents the results of a long-term N fertilization experiment in the Loch Vale watershed of Rocky Mountain National Park and presents a conceptual model hypothesizing environmental controls on ecosystem responses to N fertilization. The experiment consisted of annual 25 kg N ha-1 application of NH4NO3 fertilizer to three 30 x 30 m subalpine forest plots from 1996 to 2017. Soil, plant, and lysimeter samples were collected over the course of the experiment to address three research goals. First, determine whether increased N input leads simply to increased N output, or whether observable ecosystem effects result. Second, describe changes in the ecosystem responses over time and determine the controls that govern those changes. Third, identify results of the experiment that may generalize to other coniferous forests around the world. The results show that N fertilization causes ecosystem effects in Loch Vale which vary over time and space due to the influence of hypothesized controlling factors such as soil moisture, pH, and plant uptake of N. The results of the Loch Vale experiment suggest that impacts of excess N on boreal forests may include increased plant growth where soil moisture is adequate, but when coupled with drought may lead to increased rates of nitrification, N mineralization, NO3- leaching, and soil acidification.
2020 Spring.
Includes bibliographical references.
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forest soils
subalpine forest
long-term fertilization
ecosystem science
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