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Measurement of Within Tree Density Variations in Douglas-fir (pseudotsuga Menziesii (Mirb.) Franco) Using Direct Scanning X-ray Techniques

出版	Oregon State University, 1988
URL	http://books.google.com.hk/books?id=cM7XNwAACAAJ&hl=&source=gbs_api

註釋The objectives of this study were to 1) upgrade the direct scanning X-ray wood densitometer and then verify its capabilities by 2) categorizing within-tree patterns of variation in two Douglas-fir (Pseudotsuga menzeisii (Mirb.) Franco) trees, 3) evaluating the breast height specimen density as a measure of whole tree density and 4) measuring within stand density variation in twenty trees to determine the minimum sample size required to estimate wood quality for a stand. Wood quality for the purposes of this study was defined by wood density and its components, juvenile wood volumes and rate of growth. The direct scanning X-ray densitometer has been designed and implemented to provide access to within tree ring density data of thin wood sections -- 1.5 to 2.5 mm thick -- up to 340 mm in length. Menu driven software controls the scanning system and facilitates a variety of data acquisition utilities. Acquired X-ray attenuation data is converted to density data, plotted for operator review and then reduced to obtain nine data values for each tree ring, in a scan specimen. Within tree density variation due to sample position, north or south, was not significant at the 95% confidence level. Radially, density initially decreased in successive rings from the pith for a period of three to five years and then gradually increased to a maximum at the bark. Disk density decreased with tree height due to the decreasing mature wood growth rings. A transition in density characteristics between 15-20 years signaled a transition from juvenile to mature wood characteristics. Juvenile wood decreased in volume with increasing tree height due to a decreasing rate of growth. Breast height densities were higher than average stem densities. The correlations between breast height and tree densities suggest that breast height specimens do provide a measure of stem density and its variability. Stand density variability dictates a sampling of approximately ten trees to get an accurate measure of average stand density. Considering some of the problems incurred with increment core sampling I would suggest that twenty cores be taken from a stand and then the ten best be used to evaluate stand density.