Understanding forest floor accumulation and nutrient dynamics in a loblolly pine plantation regenerated with varying forest floor and slash retention

by 1971- Zerpa, Jose Luis

ZERPA, JOSE LUIS. Understanding Forest Floor Accumulation and Nutrient Dynamics in a Loblolly Pine Plantation Regenerated with Varying Forest Floor and Slash Retention. (Under the direction of H. Lee Allen.) The effects 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 objectives were to determine the effects of removing, leaving unaltered, or doubling the forest floor and slash material, on forest floor mass, nutrient dynamics, litterfall, foliar nutrition, mineral soil properties, and stand yield. The parameters measured included ash-free weight, nitrogen (N), carbon (C), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), sulfur (S), boron (B), copper (Cu), and zinc (Zn) concentrations in the forest floor, litterfall, and foliar samples, N extracted from ion exchange membranes (IEM) from the forest floor, potential mineralized N and IEM-N, total C and N, exchangeable Ca, Mg, K, and sodium (Na), extractable P and Mn, pH, and bulk density from the mineral soil, and tree volume. Forest floor mass and nutrient content in the doubled treatment were significantly greater than in the other two treatments. The doubled accumulated 25, 45 and 350% more forest floor mass and 56, 56, and 310% more N than the control treatment in the L, F, and H layers, respectively, the other nutrients followed similar accumulation patterns. IEM and potential mineralized NO3--N in the mineral soil were significantly higher in the doubled treatment. No significant treatment differences were found in the mineral soil properties assessed. The positive effect of doubling the forest floor on soil N availability was well reflected by the fact that the greatest foliage production (indicated by litterfall) and stand yield were found on this treatment. In addition, this linkage was indicated by strong positive correlations among stand yield, litterfall, potential nitrification, and IEM extractable NO3--N. Greater amounts of available N in the mineral soil and most likely in the forest floor on the doubled treatment apparently resulted in a feed forward effect with greater growth and in turn greater litterfall and accumulation of new forest floor material (L and F layers). In addition, the retention of more forest floor material (at least in the manner it was done in this study) apparently resulted in slower decomposition of the retained material in a non linear proportion relative to its original mass. This in turn has resulted in long term increases in soil available N through the 10th year following plantation establishment.