Removal of stumps from a Phellinusweirii infested site and fertilization affect mortality and growth of planted Douglas-fir

Abstract

A 2 × 4 set of factorial treatments of stump removal in combination with nitrogen fertilization was applied to 0.04-ha circular plots within a clearcut on the west slope of the Cascade Range (44°21′N, 122°39′W). Treatments included stump removal (either all stumps removed or the plot left undisturbed) and broadcast fertilization with ammonium nitrate (0, 336, 672, or 1345 kg N•ha−1). Diameter at breast height and height of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings, planted 4 months after treatment, were recorded five and nine seasons after outplanting. Soil bulk density in the upper 20 cm was measured with a single-probe neutron densimeter. Stump removal reduced the number of seedlings killed by laminated root rot (Phellinusweirii (Murr.) Gilb.) but had no significant effect on seedling growth. Stump removal increased soil bulk density only 7% as measured 9.7 years after treatment. Fertilization increased the growth in diameter at breast height, and height growth of the seedlings. Elevated total soil nitrogen could still be detected on fertilized, nonstumped plots 9.7 years after treatment.