Mitigation of harvesting disturbances on a forested wetland in the South Carolina lower coastal plain
Wet site timber harvesting often results in rutted and/or compacted soils. These impacts damage inherent site and soil properties and can reduce subsequent pine seedling survival and growth. Site preparation treatments such as bedding, disking, and fertilization are often employed on harvested sites to mitigate these impacts; however, their effectiveness has not been fully documented. Moreover, a distinction between rutting and compaction has not been made in previous research. This study’s objectives were to quantify the effects of rutting and compaction on site and soil properties and pine seedling growth and survival, and to quantify the effectiveness of bedding, disking, and fertilization in mitigating these impacts.
Six wet pine flats were salvage logged following Hurricane Hugo in the fall of 1989. High soil moisture conditions during the salvage operations resulted in compaction and rutting damage. Two studies were established to quantify the effects of trafficking on the functions and productivity of wetland sites. One study addressed soil compaction while the other addressed soil rutting. Each study consisted of three sites, each containing four trafficked and four untrafficked plots.
Four site preparation treatments, one on each disturbance plot, were installed in the fall of 1991. The four treatments were 1) no treatment, 2) bedding, 3) disking, .and 4) disking and bedding. The treatment plots were further split with half of each plot receiving 227 kilograms per hectare of 10-10-10 fertilizer. Genetically improved seedlings were hand-planted on the treatment plots in February, 1992.
The site preparation treatments did not completely ameliorate compaction or rutting effects on pine seedling growth and survival. Rutting reduced pine seedling second-year height growth, total volume, and survival by 43, 90, and 9 percent, respectively. Compaction reduced second-year height growth by 31 percent and seedling survival by 14.5 percent. Bedding resulted in 35 and 106 percent greater second-year height growths and 117 and 421 percent greater seedling volumes than disking on the rutted and compacted sites, respectively. Phosphorous fertilization had an additive effect to the site preparation treatments and increased pine seedling height growth by 54 and 65 percent and seedling volume by 125 and 155 percent on the rutted and compacted sites, respectively. The factors that affected pine seedling growth and survival were water supply and movement and phosphorous supply.
Management implications for wetland sites suggested by this study are as follows: 1) avoid rutting and compaction when possible, 2) schedule wet-site harvesting during the driest periods of the year, 3) use specialized wet-site harvesting equipment when needed, and 4) use bedding and fertilization for site preparation.