摘要 : A ponderosa pine (Pinus ponderosa)-Douglas fir (Pseudotsuga menziesii) forest (PP/DF) and a lodgepole pine (Pinus contorta)-Engelmann spruce (Picea engelmannii) forest (LP/ES) located on the eastern slopes of the Cascade Mountains... 展开 A ponderosa pine (Pinus ponderosa)-Douglas fir (Pseudotsuga menziesii) forest (PP/DF) and a lodgepole pine (Pinus contorta)-Engelmann spruce (Picea engelmannii) forest (LP/ES) located on the eastern slopes of the Cascade Mountains in Washington state, USA, were examined following severe wildfire to compare total soil carbon and nitrogen capitals with unburned (control) forests. One year after fire, the average C content (60 cm depth) of PP/DF and LP/ES soil was 30% (25 t ha-1) and 10% (7 t ha-1) lower than control soil. Average N content on the burned PP/DF and LP/ES plots was 46% (3.0 t ha-1) and 13% (0.4 t ha-1) lower than control soil. The reduction in C and N in the PP/DF soil was largely the result of lower nutrient capitals in the burned Bwhorizons (12-60 cm depth) relative to control plots. It is unlikely that the 1994 fire substantially affected nutrient capitals in the Bw horizons; however, natural variability or past fire history could be responsible for the varied nutrient capitals observed in the subsurface soils. Surface erosion (sheet plus rill) removed between 15 and 18 t ha-1 of soil from the burned plots. Nutrient losses through surface erosion were 280 kg C ha-1 and 14 kg N ha-1 in the PP/DF, whereas LP/ES losses were 640 and22 kg ha-1 for C and N, respectively. In both forests, surface erosion of C and N was～1% to 2% of the A-horizon capital of these elements in unburned soil. A bioassay was used to compare soils from low-, moderate- and high-severity burn areas relative to control soil. In both forests, low-severity fire increased lettuce yield by 70-100% of controls. With more severe fire, yield decreased in the LP/ES relative to the low-intensity burn soil; however, only in the high-severity treatment was yield reduced(14%) from the control. Moderate- and high-severity burn areas in the PP/DF were fertilized with～56 kg N ha-1 four months prior to soil sampling. In these soils, yield was 70-80% greater than the control. These results suggest that short-term site productivity can be stimulated by low-severity fire, but unaffected or reduced by more severe fire in the types of forests studied. Post-fire fertilization with N could increase soil productivity where other environmental factors do not limit growth. 收起