Short- and long-term effects of site preparation, fertilization and vegetation control on growth and stand development of planted loblolly pine

Short- and long-term effects of high and low site preparation intensity, fertilization at planting and vegetation control on growth and stand development were examined in a study that was established on six sites in southeastern USA. The study was established in 1979-1980, and growth after the 18th growing season is reported. The high-intensive site preparation improved long-term stand volume growth. Evidence suggests that the main long-term effect of the intensive site preparation was a reduction in competition from hardwoods. Herbicide treatment improved seedling establishment and early growth, but growth during the last period of measurements (14-18 years after planting) were lower in the herbicide-treated plots as compared to plots without herbicide treatment when herbicides were combined with intensive site preparation. Fertilization at planting, in combination with high-intensive site preparation, improved volume growth during the first 10 years after planting, while fertilization at planting in combination with low-intensive site preparation had little effect on volume growth. The hypothesis that low variability in the seedling stage due to intensive site preparation will lead to low variability in the mature stands with a subsequent reduction in self-thinning was examined. The low site preparation intensity had higher coefficient of variations of stem volumes, and higher mortality. However, the difference in mortality was probably partly a result of differences in competition from hardwoods, and it was not possible to separate the importance of reduced variability from reduced competition from hardwoods. Fertilized plots had lower variability than non-treated control plots but there was no significant difference in mortality between the two treatments. Therefore, it was concluded that reduced variability in the seedling stands, as a result of intensive regeneration methods that reduces environmental heterogeneity, reduces the variability in the mature stands. However, it could not be inconclusively proved that lower variability in the mature stands will result in reduced or postponed self-thinning. (C) 2002 Elsevier Science B.V. All rights reserved.