Potential above-ground biomass losses from severe soil rutting during wet weather timber harvests of coastal plain loblolly pine (Pinus taeda) plantations mitigated by mechanical site preparation

Extensive areas of pine forests on wet mineral soils in the southeastern United States are harvested during nearly saturated soil conditions. Harvest trafficking during wet conditions can alter soil physical properties related to forest productivity, however mechanical site preparation can potentially ameliorate harvest induced trafficking disturbances. In 1996 three loblolly pine (Pinus taeda) stands were harvested in the coastal plain during Wet and Dry conditions (30-40% vs 10-15% volumetric soil moisture). Five treatment combinations of harvest conditions-site preparation (Wet-Flat, Dry-Flat, Wet-Bed, Dry-Bed, Wet-Mole Plow) were operationally replicated three times. Study objectives were to quantify treatment effects on above-ground productivity 16 years post treatment. After 16 years, above-ground biomass was greater (p-value ⩽ 0.05) in the intensive Wet-Mole Plow treatment (402.9 Mg ha−1, ±6.72 Mg ha−1). Wet-Flat (372.7 Mg ha−1 ± 6.59 Mg ha−1), Dry-Flat (368.6 Mg ha−1, ±7.14 Mg ha−1), and Wet-Bed (368 Mg ha−1±6.8 Mg ha−1) produced significantly less biomass than Wet-Mole Plow, but were not significantly different from each other. Dry-Bed produced the least above-ground biomass (319.3 Mg ha−1±6.76 Mg ha−1). Wet treatments were severely disturbed, yet comparisons of Wet and Dry site preparation indicated few long-term productivity effects. Exact mechanisms of recovery were likely influenced by inherent site fertility, mixed clay mineralogy, and drought during stand establishment. Overall, this research indicates that above-ground productivity was increased by drainage/aeration effects of Wet-Mole Plow and wet weather harvesting and severe soil disturbance had minimal long-term effects on aboveground productivity of loblolly pine.