Slash burning effects on soil and water chemistry in southeastern Alaska

ABSTRACT:

Stream water samples and soil samples were analyzed to determine the effects of slash burning on soil and water resources in the coastal hemlock-spruce [western hemlock, Tsuga heterophylla (Raf.) Sarg., and Sitka spruce, Picea sitchensis (Bong.) Carr.] forests of southeastern Alaska. A comparison of water samples from above and below the burned area showed that slash burning after timber harvest increased total phosphorus and potassium concentrations in streamflow. Suspended sediment concentrations and optical turbidity (NTUs) exhibited variable relationships. Suspended sediment concentrations were significantly greater below the burned area, but no sample exceeded Alaska's water quality standard of 5.0 NTUs. A comparison of soil samples from an adjacent logged but unburned area with samples from the burned area showed no reduction in the depth of the soil organic horizon as a result of burning. Neither did the nitrogen content in the organic horizon change after burning, but burning after timber harvest significantly reduced the potassium and magnesium contents of the horizon. What changes in soil and water resources did occur as a result of timber harvest and slash burning will not reduce site productivity or result in long-term degradation of these resources.