Effects of Vegetation Control and Organic Matter Removal on Soil Water Content in a Young Douglas-Fir Plantation

We evaluated the effects of vegetation control and organic matter (OM) removal on soil water content (SWC) in a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation from age 3 through age 5. Treatments were presence versus absence of vegetation control through year 5 and bole-only harvest of the previous stand versus total-tree harvest of the previous stand including removal of all coarse woody residues. In the presence of vegetation control, SWC was approximately 0.02 to 0.04 m3-m-3 greater between depths of 10 and 60 cm; the effect was greatest from July to September. Soil water content was negatively correlated with percentage cover of competing vegetation and positively correlated with tree diameter growth across all treatments. Soil water content at depths between 10 and 100 cm did not differ between OM removal treatments. Accurate measurement of SWC required a soil-specific instrument calibration. On this highly productive site with high annual precipitation, SWC was greater through plantation age 5 when competing vegetation was controlled.