Specific Gravity Studies of Young-Growth Southwestern Ponderosa Pine

A study was made to determine the average specific gravity at breast height, as well as the tree to tree variation in young-growth stands of ponderosa pine. A total of 544 increment cores were made available from a soil-site study which sampled trees in the range of 80 to 120 years of age in 68 plots located in Arizona and New Mexico. A total of 477 valid observations was complied which resulted in a mean specific gravity before extraction of 0.4159 and a mean specific gravity after extraction with one-third ethyl alcohol and two-third benzine solution of 0.3741. The specific gravity within and between trees, as well as between individual stands of trees, is subject to considerable variation. The variation of specific gravity in extractive-free wood appears to be less than in unextracted wood. Latewood accounts for about 20 percent of the variability in specific gravity. The growth rate is not highly correlated with specific gravity. With the exception of elevation, only those variables associated with the tree appear to have any appreciable relationship with specific gravity.

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