Doctoral Dissertations

Date of Award

12-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major Professor

H. H. Shugart

Committee Members

Edward R. Buckner, John C. Rennie, Darrell C. West

Abstract

The purpose of this research was to investigate the nature and extent of intertree and interspecies competition in a mixed-aged, mixed-species mesic hardwood forest in southern Appalachia. The study focused on competition and growth relationships as influenced by com munity structure and development, climatic conditions and species interaction.

Sampling involved coring and mapping study trees and neighbors above 2.54 cm dbh on circular .08 ha plots. Study plots were selected to maintain site homogeneity and species complement with respect to pure and mixed stands of tulip-poplar,Liriodendron tulipifera L., and white oak, Quercus alba L. Each plot was centered about subject tree pairs composed of pure and mixed associations of these two species. Measurements of diameter, crown class and core orientation were taken along with tree azimuth and distance from plot center. Cores were crossdated and measured to determine age, sapwood basal area and ring width for years 1930 to 1981.

A computer program was written to recreate plot and tree con figurations in order to calculate and test newly proposed competition measures along with established indices. These indices were evaluated on their performance under different competitor selection criteria and assumptions. Paired tree comparisons were employed to examine competitive intensity between trees in intra- and inter-specific associations.

Forest structure dictated the primary competitive influence in these mesic, mixed-aged, mixed-species stands. While horizontal spacing and density of trees has been emphasized in the design of most competition indices, vertical stratification and differential resource partitioning of light proved most significant. New competition indices, sapwood basal area and a crown-area estimate, demonstrated the highest correlations of all measures evaluated. Success of these indices was attributed to their strong relationship to leaf area and a tree's structural position and expanse to intercept available light. Increased spatial and positional variation in stand structure through time accounted for stronger competitive relations in latter growth years. The relationship between competition and annual growth was strengthened in years of climatic extremes, such as drought years. Differences in competitive ability by species was demonstrated. White oak proved more drought tolerant and a more intense competitor. Results indicated that both intra- and inter-specific association can give rise to greater competitive interaction depending on the species, stand and site conditions involved.

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