Soil nutrient contents and fluxes in semi-arid lodgepole (Pinus contorta [Dougl.] ) and jeffrey pine (P. jeffreyi [Grev. and Balf.]) stands of the eastern Sierra Nevada mountains are described and compared to those in the Integrated Forest Study (IFS) sites [Johnson and Lindberg, 1992]. These Sierran forests, like others in the southwestern US, have very low N, S, and H+ fluxes compared to more humid forests. Base cation fluxes in these Sierran forests are high relative to more humid forests, however, reflecting the high base status of the soils, inputs from nearby desert systems, and high rates of soil weathering. Soil C and N contents in these Sierran forests are low compared to those in more humid forests, probably because of lower primary productivity and more frequent fire. Soil extractable P pools in these Sierran forests vary by two orders of magnitude and are strongly influenced by parent material. As in most snow-dominated systems, pulses of NO3- are released from the melting snowpack each spring in the Sierran forests. Nitrogen released from melting snowpack is retained in the soil in most cases, but there are substantial springtime pulses of NO3- in streamwaters during dry years. Budget calculations indicated that N losses during fire (both wildfire and prescribed fire) and N gains associated with post-fire N-fixing vegetation are an order of magnitude greater than N inputs and outputs via solution phase.
AGU Index Terms: 1615 Biogeochemical processes (4805); 1806 Chemistry of fresh water; 1615 Biogeochemical processes
Keywords/Free Terms: nitrogen,fire,deposition,leaching,sulfur.
Global Biogeochemical Cycles 97GB01750
Vol. 11
, No. 4
, p. 673