TIMBER HARVESTING AND LONG-TERM PRODUCTIVITY - WEATHERING PROCESSES AND SOIL DISTURBANCE

Both timber harvesting and amelioration practices can cause chemical a nd physical changes to the soil. These changes can affect factors whic h alter soil mineral stability and weathering rates, potentially chang ing inputs to the nutrient cycle. This paper discusses possible effect s of harvesting and ameliorative practices on soil mineral stability a nd weathering. It also presents data from a case study of harvesting i mpacts in New Zealand. A soil disturbance study established in 1981 wa s examined in 1990 for potential effects of soil disturbance on weathe ring and soil nutrient availability. Post-harvesting site treatments i ncluded O horizon preserved, O horizon removed, and O and A horizons r emoved followed by compaction. Results showed that removal of the O ho rizon greatly reduced the available nutrient pool. Changes in concentr ations of solution Si also indicated that mineral equilibrium had been affected in the surface soil horizons of the two disturbance treatmen ts. Fine-root and mycorrhizae biomass was reduced with both disturbanc e treatments. A comparison of soil nutrient inputs and outputs suggest s that weathering inputs must provide most of the available nutrients with the disturbance treatments.