Soil changes and tree seedling response associated with site preparation in Northern Idaho

Abstract

Conifer regeneration in western North America is often hampered by low soil moisture, poor soil nutrient status, and competing vegetation. Three site preparation techniques were evaluated at two different elevations in northern Idaho as potential remedies for these problems: (1) soil mounds without control of competing vegetation, (2) soil mounds with herbicidal control of competing vegetation, and (3) scalping (removal of soil surface organic horizons and mineral topsoil). Treatments were evaluated for effects on soil nutrient levels, soil physical properties, and the growth of Douglas-fir (Pseudotsuga menziesii var. glauca) and western white pine (Pinus monticola) seedlings. Both species generally grew best when planted in the mounded treatment with competing vegetation removed and worst after scalping. Mounding with herbicide application resulted in the lowest bulk density, best seedling growth, and increased water availability. Mounding may be a viable site preparation method in the Inland Northwest on less productive sites that have severe competition. Scalping, especially when competition was not a problem, generally did not produce favorable seedling growth responses. Scalping may also reduce longer term seedling growth by removing surface organic matter.