Masters Theses

Date of Award

8-2000

Degree Type

Thesis

Degree Name

Master of Science

Major

Forestry

Major Professor

John C. Rennie

Committee Members

Ray Wells, Ron Hay, Michael Huston

Abstract

Tree-ring increment cores were collected from 106 yellow-poplar (Liriodendron tulipifera) trees at Walker Branch Watershed, which is near Oak Ridge, Tennessee. Tree-ring widths were measured and converted to basal area increments (BAI's). BAI data were used to assess the relationship between temporal and spatial variation in moisture availability and variation in annual growth indexed by BAI. There are two major long-term growth trends in the mean BAI chronologies. These trends are an increase in BAI that occurs between 1961 and 1985 and a major decline in BAI that begins in 1986. Both of these trends are related to changes in climate. The first trend is associated with the climate becoming wetter than normal and the second trend is associated with a severe drought that occurred between 1985 and 1988. In 1989, the drought ended and climate became normal to wetter than normal; however, BAI did not recover after the drought ended. It is argued that the growth decline that lasted throughout the 1990's is a result of damage to the trees caused by extreme drought stress. The study also found that fine-scale differences in topography are related to variation in BAI. Topographic index. In (α/ tanβ), was used to estimate the average moisture availability of the tree locations on Walker Branch Watershed. Xeric locations on Walker Branch Watershed have higher coefficients of variation in BAI than did mesic locations. Using multiple linear regression to perform response function analysis, it is shown that mean BAI chronologies from xeric locations have a higher association with variance in monthly climate variables than do mean BAI chronologies from mesic and intermediate locations.

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