Doctoral Dissertation Research: Calibration and Application of Sedimentary Proxies in Evaluating Spruce Beetle Outbreaks from the High Plateaus of Utah

University Of Utah, Salt Lake City UT

Investigators

Abstract

Bark beetles (Dendroctonus spp.) and wildfire are significant disturbance agents in conifer forests of western North America. Understanding the occurrence, the ecological significance and how these two disturbances interact over long time scales and under different climatic regimes is import to contextualize current forest dynamics. Methodologies exist for reconstructing past fire episodes over the Holocene (last ~10,000 years) using sedimentary charcoal from lake sediments. However, no methodology currently exists for assessing bark beetle disturbances over similar timescales using lake sediments, despite their ecological significance. The ecological response of subalpine forests to a spruce beetle infestation is generally that subalpine fir (Abies lasiocarpa) and other understory components increase in abundance and productivity following mortality of mature spruce. The invigorated growth of the understory is attributed to increased availability of sunlight, moisture and nutrients. The 'release' of the understory component following severe outbreaks is well documented in historic stand inventory data as well as in tree ring records. These changes in stand structure are reflected in the pollen record. Using pollen records obtained from six subalpine basins in Utah, a calibration study was performed emphasizing changes in pollen deposition concurrent with several 20th century spruce beetle (D. rufipennis) outbreaks. These changes generally reflect an exchange of spruce pollen for fir and other understory taxa. The research supported here will apply the calibration set to pollen data from three Holocene-length sediment cores retrieved from the Wasatch Plateau, Markagunt Plateau and Aquarius Plateau, located in central and southern Utah. The Markagunt Plateau site is the most temporally resolved core and will be dated and analyzed at multidecadal resolution to further refine forest dynamics associated with spruce beetle infestations. This project will provide an important step forward in using lake sediments to reconstruct non-fire disturbances, specifically for spruce beetle in subalpine forests. Developing long term records of forest ecology and disturbance are important resources for land managers and their respective agencies. The research conducted here will provide an important baseline of understanding with which to interpret recent bark beetle outbreaks in western conifer forests. The support of this research through a Doctoral Dissertation Research Improvement award will enable a promising student to establish a strong environmental research career.