REMOVAL OF STUMPS FROM A PHELLINUS-WEIRII INFESTED SITE AND FERTILIZATION AFFECT MORTALITY AND GROWTH OF PLANTED DOUGLAS-FIR

A 2 X 4 set of factorial treatments of stump removal in combination wi th nitrogen fertilization was applied to 0.04-ha circular plots within a clearcut on the west slope of the Cascade Range (44 degrees 21'N, 1 22 degrees 39'W). Treatments included stump removal (either all stumps removed or the plot left undisturbed) and broadcast fertilization wit h ammonium nitrate (0, 336, 672, or 1345 kg N.ha(-1)). Diameter at bre ast height and height of Douglas-fir (Pseudotsuga menziesii (Mirb.) Fr ance) 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 (Phellinu s weirii (Murr.) Gilb.) but had no significant effect on seedling grow th. 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 s oil nitrogen could still be detected on fertilized, nonstumped plots 9 .7 years after treatment.