Crown area is an important factor in determining stem development. This study examined the changes in stem diameter per unit area of crown due to treatment with fire, herbicide, fertilizer, and tree-thinning practice. The experimental sites were mid-rotation loblolly pine (Pinus taeda) plantations that were thinned one year before treatment. Site 1 was strictly row-thinned and Site 2 was thinned by and within each row. Five replicates were installed on each site. Each replicate consisted of 8 subplots (0.1 ha) containing a central 0.04 ha measurement plot. A randomized-block split-plot design was used at each site, with fertilizer as the whole-plot factor and vegetation control treatment as the subplot factor. The herbicide treatment (approximately 4.5 L ha-1 Chopper?, 2.5 L ha-1 Accord?, 11.2 L ha-1 Sun-It II oil, and 76.7 L ha-1 water) was applied in October, 1999. Prescribed burning was performed in March, 2000, and fertilizer (224 kg ha-1 N and 28 kg ha-1 P) was applied in April following the burn. The height and diameter of each tree was measured at plot establishment (1999) and in December, 2000. Individual tree crown area was measured in June, 2000. A leaves-to-tree (LT) metric, defined as the ratio of a tree's diameter (cm) in December, 2000 to crown area (m?) in June, 2000 was used to examine the impact of the various factors. Herbicide affected growth differently at the two sites; growth was increased at Site 1, but decreased at Site 2, relative to their respective controls. The results were unaffected by the use of fertilizer. Fire had a negligible effect on growth at both sites, with and without fertilizer. Herbicide and fire were additive at Site 2 but antagonistic at Site 1. The results suggest that thinning practices can significantly alter the impact of herbicides and fire on tree growth. Data from the second (and final) year of the study will be available in December, 2001.
Marino, L. M.; Oswald, B. P.; Farrish, K. W.; Williams, H. M.; and Unger, Daniel R., "Growth Reponse of Loblolly Pine to Intermediate Treatment of Fire, Herbicide, and Fertilizer: Preliminary Results" (2002). Faculty Publications. 512.