Rotation-Length Effects of Diverse Levels of Early Competition Suppression and Precommercial Thinning on Loblolly Pine Stand Development

At a loblolly pine plantation in central Louisiana, a 28-year study was conducted with the objectives of determining the following: whether suppressing herbaceous (HERB), woody (WOOD), and total noncrop vegetation (TOTAL) for the first 5 years of a rotation altered loblolly pine growth and yield; whether operational-type herbicide mixtures applied in the first year of the rotation resulted in loblolly pine growth and yield similar to those of HERB, WOOD, and TOTAL treatments; and whether precommercial thinning led to greater magnitude and/or longer persistence of herbicide treatment effects on loblolly pine growth and yield. The greatest tree growth increases in magnitude and duration resulted from the TOTAL treatment; height, diameter, and weight increases persisted through ages 20-28 years. Controlling herbaceous vegetation produced greater tree growth increases in magnitude and duration than suppressing woody vegetation. Operational mixtures had growth gains and yields secondary only to the TOTAL treatment. Precommercial thinning did not affect the degree or duration of loblolly pine responses to vegetation suppression treatments, but it increased tree height, diameter, and weight for the remainder of the rotation, leading to earlier development of higher valued forest products.