Masters Theses

Date of Award

8-1995

Degree Type

Thesis

Degree Name

Master of Science

Major

Geography

Major Professor

Sally P. Horn

Committee Members

Carol Harden, Mike Huston

Abstract

Farms on the present-day Oak Ridge Reservation, Tennessee, were abandoned simultaneously in 1942 when the federal government acquired the land for constructing atomic weapons facilities. Variations in land use and soil degradation among agricultural fields provided a number of starting points for vegetation succession. After a half-century, forests have reclaimed the abandoned fields. Using late-1930s black-and-white aerial photographs, I identified four pre abandonment site types on south-facing slopes of ridges at the Oak Ridge Reservation: a) severely eroded pastures, b) pastures showing intermediate levels of erosion, c) pastures exhibiting few signs of erosion, and d) closed-canopy forest. During summer 1993, I used twenty circular plots to sample the woody vegetation on abandoned pastures. In addition, I obtained information about closed-canopy forest sites from plot data recorded for the Walker Branch Watershed Project. I then compared current community composition, size-class distributions, and diversity (richness and Sharmon diversity) of the vegetation on the four site types. Fifty-year old forests that have developed on intermediate and severely eroded pastures are dominated by light-demanding colonizers typical of early succession — shortleaf pine (Pinus echinata), Virginia pine (P. virginiana), and yellow-poplar (Liriodendron tulipifera). Fifty-year old forests on the least eroded pastures are hardwood stands dominated mainly by oaks (Quercus spp.), hickories (Carya spp.), and yellow-poplar. A few pines remain in some of the stands. Succession appears to be proceeding most rapidly on the pastures that were least eroded at the time of abandonment, probably indicating that plant productivity is higher on these pastures than on those that were more severely degraded. The older forests that possessed closed canopies in 1942 are dominated by white oak (Quercus alba) and chestnut oak (Q. prinus), with red maple (Acer rubrum), yellow-poplar, and a few other hardwood species present. Tree species diversity generally increases along inferred productivity gradients. However, forests developed on a few of the most productive sites exhibit relatively low diversity. It appears that the relationship between productivity and diversity in these fifty-year old stands might best be characterized as unimodal, with sites possessing intermediate levels of productivity exhibiting higher diversity than more productive or less productive locations. Low diversity at the most productive sites would be the expected outcome of competitive exclusion.

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