Establishment treatments affect the relationships among nutrition, productivity and competing vegetation of loblolly pine saplings on a Gulf Coastal Plain site

Abstract

After cultural treatments such as site preparation, release and fertilization, changes in the supply of mineral nutrients relative to each other and shifts in the composition of vegetation may have a delayed effect on the nutrition, carbon partitioning and growth of forest trees. This study was conducted to evaluate the influence of early management options that control vegetation and fertility on the nutrition and productivity of a young loblolly pine ( Pinus taeda L.) plantation on a phosphorus-deficient site in the Gulf Coastal Plain. Two levels each of herbicide application, fertilization and litter addition were applied in a factorial arrangement to three open-pollinated families of newly planted loblolly pine seedlings. Competing vegetation was evaluated after three growing seasons, loblolly pine nutrition and tannin synthesis were evaluated after four growing seasons and loblolly pine productivity was quantified after five growing seasons. Fertilization and herbicide application increased the growth and decreased the foliar tannin concentration of loblolly pine. Herbicide application also increased the potassium concentration of loblolly pine foliage. A negative correlation between foliar tannin and potassium concentrations was found on plots that were fertilized with nitrogen and phosphorus. On southern pine sites that are fertilized with phosphorus, the accelerated growth of planted pine and invading vegetation may create new nutrient limitations. Where phosphorus is limiting, however, nutrient utilization may not be great enough for new deficiencies to develop. Loblolly pine stand productivity and foliar nutrient concentrations were affected by genetic family and the foliar calcium and magnesium concentrations of loblolly pine families responded differently to the establishment treatments. We also found that the establishment treatments influenced the occurrence of herbaceous and woody competitors. We hypothesize that corresponding treatment effects on exchangeable cation concentrations and pH of the soil were caused by changes in vegetation.