Doctoral Dissertation Research: Treeline Responses to Climate Change in High-Elevation Landscapes of Western Montana

University Of Tennessee Knoxville, Knoxville TN

Investigators

Abstract

The past and present positions of treeline are controlled by climatic conditions and act a recorder of past climate change. The Medieval Warm Period (MWP) and subsequent Little Ice Age (LIA) are considered characteristic examples of the warm and cold phases of millennial-scale climatic fluctuations that have reoccurred throughout glacial and interglacial periods. A gap currently exists regarding the spatial and temporal record of climatic fluctuations for high-elevation sites in western Montana. The goal of this doctoral dissertation research project is to: (1) conduct comparative analyses of tree growth responses to climate changes using the tree-ring record from trees growing in selected sites in western Montana, (2) evaluate the summer temperature response to volcanic aerosol forcing at treeline, (3) assess the mechanism, anatomy, and consequences of frost-ring formation and temperature at treeline, and (4) synthesize these analyses to assess past and present treeline dynamics in relation to climate variability. Examination of the range of variation in climate is a significant component for understanding the spatial and temporal dynamics of past climate shifts and the potential behavior of the climate system in the future. To analyze the effects of global climate shifts on treeline dynamics, the researchers will collect increment cores and cross sections from selected whitebark pine and subalpine fir trees growing below, at, and above the present treeline. In addition, samples will be collected from remnant wood above treeline to aid in locating past treeline fluctuations and increase understanding of past forest structure. The results of the proposed dendroclimatic and dendroecological research will result in the development of (1) an increased knowledge of the effects of temperature change on the growing season of whitebark pine and subalpine fir, (2) improved understanding of the effects of volcanic forcing of temperatures at a species ecological limit, (3) the development of the subalpine ecological response to climate variability over century (and possibly millennial) time scales, and (4) increase comprehension of the effect of temperatures experienced during the MWP and subsequent LIA on ecosystem processes. The results of this study will serve to fill gaps in our understanding of the role of climate as a primary influence of ecosystem dynamics at high-elevation sites in the northern Rocky Mountains. Therefore, the upper treeline in the western United States should be targeted for a more systematic sampling of climate sensitive specimens in the future to increase our knowledge of past climatic shifts, further quantify the effects of climate shifts on high elevation ecosystems, and to help predict future climate fluctuations and how they may affect the fluctuation in treeline advance or retreat. This Doctoral Dissertation Research Improvement grant will provide field and laboratory support for a talented student to continue his research and academic careers.