Genetic, Growth, and Environmental Factors Affecting Specific Gravity of Loblolly Pine

Texas Forest Service has established 15 plots of 50 trees each on various sites in east Texas to study the possible affects of various growth environmental factors on specific gravity. The stands were essentially even aged and sites were as uniform as possible with the average ages of plots varying from 25 to 60 years. Considering each factor singly within a plot, the following results were obtained: l) A weak relationship between age of a tree and specific gravity, 2) a weak relationship between growth rate and specific gravity, 3) no relationship between percent of clear bole and specific gravity, and 4) a weak relationship between site and specific gravity, 5) no relationship between moistness of site and specific gravity. 6) Stand density had little or no relation to specific gravity. The maintenance of relatively high or low specific gravity from juvenile through mature wood in any one tree indicates that some type of inherent pattern may be present. On each plot of 50 trees there was usually a large spread in specific gravity despite geographical location of the plot. This variation was completely confused by age, site, growth rate and other factors. Often two trees growing side by side were phenotypically very similar but with distinct differences in specific gravity. Furthermore, trees with the most extreme specific gravities were found on different sites and with different growth rates. The results of these studies suggest that the specific gravity of any particular tree may well be determined by the specific gravity of its parents.

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