Effects of Skid Roads on Diameter, Height, and Volume Growth in Douglas‐fir

Abstract This study was conducted to measure the effects of tractor logging which occurred in 1947 upon the productivity of a subsequent stand of Douglas‐fir ( Pseudotsuga menziesii [Mirb] Franco) and to assess the degree and extent of residual soil compaction. The 4.33‐ha study area was categorized into skid roads, transition zones (3 m on each side of the skid roads), and undisturbed areas. Volume of every tree over 5 cm diameter breast height (dbh) was estimated by the tarif method. Forty trees in each category were measured for age‐growth relationships. Soil bulk densities were measured with a two‐probe nuclear densiometer. Total tree volumes per hectare for skid roads, transition zones, and undisturbed areas were 34.1, 97.2, and 128.9 m 3 ; stand densities were 693, 974, and 1,180 stems/ha, respectively. Growth reductions in the skid roads and transition zones resulted in an overall volume loss of 11.8% for the total area. An analysis of covariance showed that there was no significant difference in the slope of the tree height‐age regression lines for each of the three categories. However, there was a highly significant difference in the adjusted height means between trees from skid road and those in the other two categories. Trees growing in the skid roads took 4.1 years longer to reach breast height than those growing in the undisturbed areas. After 32 years, 25% of the entire study area was still heavily compacted (bulk density > 1.20 g/cm 3 ). Recovery from compaction has occurred in the surface 15 cm.

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