Nitrification in undisturbed mixed hardwoods and manipulated forests in the southern Appalachian Mountains of North Carolina, U.S.A.

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Abstract
This paper summarizes data on nitrification at the Coweeta Hydrologic Laboratory, in the southern Appalachian Mountains of North Carolina, U.S.A., focusing on effects of watershed treatment and vegetation type. At Coweeta, as at other United States sites, oak–hickory forests gave the lowest nitrification potentials. Nitrification potentials and nitrifier numbers were lower in oak–hickory forests of undisturbed watersheds than in disturbed watersheds. Nitrification potentials were also low in a white pine plantation, although higher than in other pine forests in the United States. In a regenerating clear-cut and in a 17-year-old successional forest at Coweeta, nitrification potential was higher in dense stands of black locust (Robiniapseudoacacia L.) than in areas where black locust was absent. In the undisturbed forests at Coweeta, low nutrient availability probably limits the size of nitrifier populations; the influence of soil pH on nitrification was unclear. In the disturbed forests, nitrification is apparently controlled by the availability of ammonium nitrogen and other nutrients.