GROWTH RESPONSE OF PINUS TAEDA TO VARYING LEVELS OF HARDWOOD CONTROL

A loblolly pine (Pinus taeda L.) plantation study was installed across the south-eastern United States by members of the Auburn University Silvicultural Herbicide Cooperative. This study was designed to quantify and model the effects of varying levels of competing vegetation on long-term pine growth. A matrix of initial stand conditions was established encompassing three site index classes, six plantation ages (0-5 years), four hardwood rootstock density classes (class limits vary by age), and absence or presence of herbaceous weed control. Five 0.13-ha treatment plots, with 0.06-ha measurement plots, were established at each location. Variation among plots was controlled by sampling and matching plots based on pre-treatment pine and hardwood tree and stand attributes. Each plot was selected for no treatment (check), total hardwood control for 1 year, or specific levels of intermediate hardwood control (one-time treatment by basal spray of herbicide). Herbaceous weed control was combined with hardwood control for certain treatments at selected locations to evaluate the impact of herbicides that control both plant components.