Does It Pay to Conduct Midrotation Competition Control and/or Fertilization? Results from Two Thinned Loblolly Pine Studies in the Coastal Plain of Georgia

The effects of midrotation competition control and fertilization were studied in two loblolly pine stands in the Coastal Plain of Georgia. The use of fertilizer or herbicide alone did not enhance wood yields above the control, which negates the cost spent to conduct these practices. The combined treatment of fertilization and herbicide promoted higher average pine annual increment and greater proportion of sawtimber. Site limiting factors, most likely both competing woody vegetation and low nutrient status, largely determined the effectiveness and priority of midrotation treatments. The economic returns of the combined treatment varied considerably depending on stumpage prices, treatment costs, and magnitude and duration of the growth response. Sawtimber prices (absolute value and relative to pulpwood and chip-n-saw) play a critical role in the marginal returns of midrotation treatments. Continued depressed sawtimber prices will discourage private landowners from investing in midrotation vegetation control and fertilization. Study Implications: Midrotation fertilization and vegetation control can be attractive silvicultural treatments to increase timber volume and economic returns. Assessment of site variables that limit growth, especially soil fertility and plant competition, must be conducted before prioritization of treatments. The economic returns of midrotation treatments vary greatly depending on treatment costs, stumpage prices, and magnitude and duration of pine growth response compared with controls. The pine growth response of particular concern is ingrowth of trees into the sawtimber size class and growth of sawtimber-sized trees. Sawtimber prices play a critical role in the marginal internal rate of return of the additional investment. Lackluster timber prices (especially sawtimber prices) may render investment in midrotation fertilization and vegetation control unattractive and have detrimental effects on timber supply and forest health of the region in the long term.