Growth response of Pinus taeda L. to herbicide, prescribed fire, and fertilizer
The purpose of this study was to determine the relative effects of selected combinations of herbicide, fire, and fertilizer treatments on the growth of mid-rotational loblolly pine (Pinus taeda L.) at two East Texas sites, and to evaluate possible mechanisms responsible for the effects. Specifically, the first objective was to determine if fire and herbicide, with and without fertilizer, increased growth of mid-rotation loblolly pine, as assessed from measurements of the change in basal area following treatment. The second objective was to evaluate the roles of crown area and available growing space as possible mechanisms explaining potential increases in tree growth. Herbicide treatment produced an increase of 5% in basal area of unfertilized trees at both sites between 1999 and 2001 (P < 0.05), but had no effect on growth of fertilized trees at either site. Prescribed fire had no effect or (in plots that had high scorch levels) had an adverse effect. On average, scorch heights were greater in plots that received herbicide (3.3 m) as compared with unherbicided plots (1.7 m) for the two sites. In addition, average scorch heights were greater in fertilized plots (2.9 m) as compared with unfertilized plots (2.1 m) at both sites. When the growth of individual trees was analyzed in relation to the amount of foliage (represented by crown area), the overall average in plots that received herbicide was 27% m−2, compared with 20% m−2 on control plots. The effect of herbicides on unfertilized trees was also analyzed on the basis of the area potentially available (APA) to support tree growth. The growth of individual trees analyzed with respect to its corresponding APA revealed that basal area growth per unit of APA values ranged from 7 to 15% m−2. However, no evidence supporting a role for APA in explaining the growth response to herbicide was found. Fertilizer increased growth irrespective of vegetation control treatments, but the specific effects of herbicide and fertilizer were not additive possibly due to limited soil moisture. Overall, herbicide use but not prescribed fire increased tree growth in the unfertilized plots at both sites, possibly by affecting mechanisms that occurred in the foliage.
Oswald, Brian P.; McInnis, L. M.; Williams, H. M.; Farrish, K. W.; and Unger, D. R., "Growth response of Pinus taeda L. to herbicide, prescribed fire, and fertilizer" (2004). Faculty Publications. 22.