Growth of young Pinus ponderosa and Pinus contorta on compacted soil in central Washington

Abstract

Growth in height, diameter, and volume was measured on 9- to 18-year-old ponderosa pine ( Pinus ponderosa) and 10- to 13-year-old lodgepole pine ( Pinus contorta) trees growing on or near compacted skid trails in the Yakima Indian Reservation in south-central Washington. Soil bulk density of the 0- to 30.5-cm deep layer was measured with a single-probe nuclear densimeter on two sides of each sample tree and in adjacent undisturbed soil. On three ponderos pine sites logged 23 years before the study, average bulk density on skid trails was 15% greater than on adjacent undisturbed soil. On a lodgepole pine site logged 14 years before the study, soil on skid trails averaged 28% greater bulk density than undisturbed soil. Total growth of ponderosa pine and the last 5 years of growth were significantly related ( P = 0.07) by regression analysis to age of trees, site index, basal area of the adjacent overstory, and the percentage of increase in soil bulk density. At the mean increase in soil bulk density, total height, diameter, and volume growth were reduced 5%, 8%, and 20%, respectively. Total growth of lodgepole pine and the last 5 years of height, diameter, and volume growth were significantly related to tree age and the percentage of soil organic matter. Increase in soil bulk density was not significantly related to growth of this species.