Water-Content Variation in the Standing Aspen Tree

The water content of pulpwood must be known for accurate evaluation of the worth of the material as a fiber resource. Aspen is an important pulpwood species in Minnesota, and the paper describes studies to determine the effect of tree location, and position of the wood both laterally and horizontally in the tree. The findings show that for summer-cut pulpwood a 50-50 assumption of wood and water by weight when green is reasonably correct, if the pulpwood contains material from all positions vertically in the tree, in the normal proportions. For winter-cut wood the proportion would be 44 percent wood, 56 percent water. Wood moisture content is higher at the bottom of the tree than the top. Discs cut at different heights, 4 feet to 40 feet above ground line, showed this variation to be 100 to 84 percent in the summer, 125 to 113 in the winter. In one location the height variation was absent for winter-cut wood. Laterally, moisture content was high at the pith, low in the adjacent heartwood, increasing through the sapwood to a maximum near the cambrial layer. Maximum moisture content in the cambrial layer, and throughout the tree generally, occurred in the winter. The findings showed that the ratio of water to wood fiber by weight was not affected by wood density. This is an interesting finding in view of the fact that void volume is lower for high-density species and seems to suggest that water is held mainly in the wood substance rather than the cell cavities. Moisture content information is also presented on bark.

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