Tuesday, 8 November 2005 - 10:00 AM
192-7

Effects of Forest Floor Accumulation and Slash Retention on Nutrient Dynamics in a Loblolly Pine Plantation.

Jose L. Zerpa, North Carolina State University, 105 East Circle Dr. Unit C, Cary, NC 27511

The productivity of loblolly pine (Pinus taeda) plantations across the Southeastern US is frequently limited by low nutrient availability. Forest floors can accumulate important amounts of nutrients over the length of the rotation due to the fact that decomposition rates are usually lower than inputs through litterfall. By the time of harvest, this accumulated layer can represent one of the largest nutrient pools in the plantation. Forest floors in these plantations have been recognized as sinks for essential nutrients such as N and P in the early stages of development and also in mid-rotation. However, the role played by this accumulation in the nutrition of the subsequent stand is poorly understood. The effect of varying forest floor and slash retention at time of regeneration were evaluated in a loblolly pine study established near Millport, Alabama 10 years after the retention treatments were imposed. The specific objectives were to determine the effects of the following treatments: forest floor removal, forest floor left in place unaltered, and forest floor doubled, on the accumulation of forest floor, nutrient dynamics, and litterfall production. The parameters measured included gravimetric measurements, total N, C, P, K, Ca, Mg, Mn, S, B, Cu, and Zn in the forest floor. Inorganic N extracted for ionic exchange membranes (IEM) from the forest floor, and potential mineralized N and IEM N from the mineral soil. The analyses showed a significant treatment effect on the nutrient accumulation pattern of the forest floor as well as improvements in the quality of the accumulated material, demonstrated by the lower C:N ratio of the litter layer in the doubled forest floor treatment. Available N assessed by IEM and potential mineralization was also significantly higher in the doubled treatment. Analyses of litterfall showed a strong correlation between forest floor accumulation and forest productivity.

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