Nitrogen and phosphorus limitation of plant productivity and ecosystem carbon storage over post-fire succession in an Alaskan boreal forest

Vaughan, Ellery Madeleine (2023) Nitrogen and phosphorus limitation of plant productivity and ecosystem carbon storage over post-fire succession in an Alaskan boreal forest. Masters thesis, Northern Arizona University.

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Abstract

The boreal forest is a critical global carbon sink. Previous studies have identified nitrogen (N) availability as the most important nutrient constraint on plant productivity in boreal forests. Nutrient availability, specifically of nitrogen and phosphorus (P), is a key constraint on net ecosystem carbon (C) balance. Wildfires influence boreal forest C, N and P pools, releasing N to the atmosphere while returning P to the ecosystem in ash. As wildfires become more frequent and severe, understanding how they influence nutrient limitation dynamics is increasingly important. Our 20-year full factorial N and P fertilization experiment across a wildfire chronosequence provides an opportunity to test how nutrient limitation might change with post-fire succession. We asked: 1) How does N vs P limitation of tree productivity change with post-fire successional stage, and 2) How is total ecosystem C storage affected by long-term fertilization? We expected to observe greater N limitation of tree growth at our youngest site and N and P co-limitation at our intermediate and oldest sites. We inventoried trees to estimate aboveground biomass and collected plant and soil samples to measure nutrient concentrations and estimate C, N and P pools. We found that N primarily limited tree growth earlier in succession when Populus tremuloides is the dominant species, nutrient availability did not limit tree growth at the intermediate stage of succession and P limited tree growth in our old Picea mariana stand. Additionally, total ecosystem C storage depended on both N and P at our young site, was marginally P limited at the intermediate site and was P limited at the old site. These results partially support our hypotheses and run contrary to the current understanding of N limitation in mature boreal forests; instead, they support the emerging paradigm of the importance of P limitation in terrestrial ecosystems. As N reaccumulates in the ecosystem following fire, N and C cycling may become constrained by the fixed amount of P in the ecosystem. In the face of climate change, P should be considered a key control over the C storage capacity of fire-prone boreal forest landscapes and their feedback to the global C cycle.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Alaska; Boreal forest; Carbon; Nitrogen; Nutrient limitation; Phosphorus; N and C cycling
Subjects:	Q Science > QK Botany
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > Biological Sciences
Date Deposited:	29 Jul 2026 20:36
Last Modified:	29 Jul 2026 20:36
URI:	https://openknowledge.nau.edu/id/eprint/6331

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