First Advisor

Melissa Lucash

Date of Award

5-20-2020

Document Type

Thesis

Degree Name

Bachelor of Science (B.S.) in Environmental Science and University Honors

Department

Environmental Science

DOI

10.15760/honors.863

Abstract

Global warming is altering the fire regime of interior Alaska, which may have cascading effects on the prevalence of forest types and species dominance across this region. Our objective was to investigate the relationship between vegetation composition and fire in the boreal forest of interior Alaska. We utilized data from over 700 plots sampled across the landscape designated as the Tanana region by the US Forest Service for Forest Inventory Analysis (FIA), as well as fire history records. We compared biomass and stem density of conifer and hardwood forest types, as well as individual tree species, across a gradient of landscape topography (uplands vs lowlands, aspect, slope, elevation), time since fire, and number of fires. Hardwood biomass was greater than conifer biomass and black spruce has far greater stem density than all other tree species. Conifer biomass was more affected by upland or lowland position and time since fire than elevation, slope (except at slopes >25%) or aspect. Conifer density was only affected by time since fire, increasing after 50 years. Hardwoods were more variable than conifers; biomass was only driven by time since fire and stem density was only driven by upland or lowland position. Several conifer and deciduous species (black spruce, balsam poplar, quaking aspen) showed a decline in biomass at sites that burned twice since 1940 compared to sites that burned once. White spruce and paper birch did not show a decline in biomass, and tamarack showed a decline in stem density. Certain elevation ranges, especially 1000-2050, were more favorable for high biomass levels of species such as white spruce and paper birch. Our results suggest that upland or lowland position and time since fire are more important variables than slope or aspect for determining forest type and species composition in this ecosystem, and that elevation is a variable that creates spaces on the landscape that may be favorable to a limited number of species. As fire increases in frequency and extent in Alaska, this may have important consequences for vegetation composition, thus creating lasting impacts on the landscape of Alaska for the foreseeable future.

Rights

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Persistent Identifier

https://archives.pdx.edu/ds/psu/33037

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