See more from this Session: Forest Soils Nutrient Dynamcis
Wednesday, November 3, 2010
Long Beach Convention Center, Exhibit Hall BC, Lower Level
The clearcut harvest of Coweeta Hydrologic Lab's WS 7 was undertaken as an interdisciplinary study of watershed level responses to forest management. Vegetation and soil sampling plots were established on the 59 ha watershed in 1975 and sampled for 2 years before harvest. Following harvest, 10 soil plots were re-established along with 4 additional plots on adjacent reference WS 2. Soil sample collections (0-10 and 10-30 cm depths) occurred each year, from 1977 until 1985, then again in 1992, 1993, 1998, and 2008. Total soil C and N and soil exchangeable Ca, Mg, and K increased significantly only in surface soils for 2 to 3 years after harvest, compared to pre-harvest levels. Following this increase, soil C and N content returned to pre-harvest levels, while cation content remained elevated. Laboratory soil incubations from 1977 to 1982 showed higher soil potential N mineralization and nitrification as well as, extractable NO3-N and NH4-N concentrations in the harvested watershed than the reference. WS 7 stream NO3-N concentrations increased during harvest in 1977, as expected, followed by a decline in 1981. In 1989, stream NO3-N concentrations began to increase again and have continued a pattern of increase and decline through the present. Continued stream NO3-N export is attributed to changes in N availability due to shifts in the vegetation community during secondary succession.