The controversy regarding commercial thinning continues to intensify as pine plantation acreage in the south increases. This controversy has caused industrial and nonindustrial landowners to re-examine the economic returns from their plantation investments. This study was undertaken to develop investment guidelines for the management of loblolly pine plantations. Computer simulation was used to evaluate the effect on present value that four future price/market scenarios, three management regimes, and three mechanized thinning systems can have on current thinning investments. When the economic returns from thinning are compared with a no-thin management regime, simulation results indicate that long-term investment advantages favor thinning only slightly, regardless of the future price/market scenario assumed. This slight difference suggests that individual forest product companies may find other reasons such as wood flow, tax advantages, and future product requirements of their manufacturing facilities to be overriding factors for engaging in commercial thinning. Generally, short-run cost and production differences between thinning systems are more significant than the long-term investment effects. Consequently, the type of mechanized thinning system employed has a negligible impact on the total investment. / Ph. D.