Date of Award:

5-2014

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Committee Chair(s)

Helga Van Miegroet

Committee

Helga Van Miegroet

Committee

Janis L. Boettinger

Committee

Astrid R. Jacobsen

Committee

R. Douglas Ramsey

Committee

James N. Long

Abstract

Social concern about climate change and the elevated level of atmospheric CO2 demands understanding carbon (C) storage and dynamics in forest soils, especially since soils are the largest C reservoir in terrestrial ecosystems, storing two thirds of total C. Quacking aspen (Populus tremuloides Michx.) is an iconic species in western United States that offers multiple ecosystem services, such as habitat and forage for wildlife and cattle, biodiversity, water yield, and C storage. A decline in quaking aspen cover has been documented during the last decades, possibly due to fire suppression and ungulate browsing. A shift from aspen- to conifer-dominated forests may modify the amount and properties of soil organic carbon (SOC) in montane forests in Utah, affecting the C balance at ecosystem or even regional level. This study tested the influence of overstory composition on SOC storage, stability (i.e., protection against microbial decomposition), and chemical composition along the transition between aspen and conifer forests in northern and southern Utah. This study indicates that increasing presence of aspen in the overstory is associated with greater SOC stability (i.e., longer residence time), but that site conditions also play an important role. Understanding the factors that control SOC dynamics can facilitate management recommendations towards increasing long-term C sequestration at those sites where vegetation exerts the strongest influence on SOC storage.

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