• Echols, R.M.
  Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Berkeley, Calif.
  

Wood density distribution within and across annual rings was measured by X-raying increment cores from two growth period in unthinned, thinned, and thinned and fertilized ponderosa pine trees. The unthinned trees decreased in growth rate and increased in wood density. Thinning increased growth rate 33.3%. Trees released but not fertilized increased in average ring width from 3.70 millimeters to 4.85 millimeters, but decreased slightly in wood density; fertilized trees increased in ring width from 3.85 millimeters to 5.15 millimeters and increased in wood density. A characteristic pattern of wood density distribution, resembling a chi-square curve, was found in all trees, with variations occurring most frequently at the highest and lowest density levels. Wood uniformity appeared to be controlled by the relative amounts of very high- and low-density wood, with high densities exercising the greatest influence. Analysis of density distribution may prove useful for characterizing wood for utilization purposes.