The effect of management on competing vegetation and the impact of competing vegetation on stand growth and structure in coastal loblolly and slash pine stands

Silvicultural practices at time of slash and loblolly pine plantation establishment in the lower coastal plain of Georgia and north Florida were examined with respect to the limits competing vegetation places on pine productivity, how these limits differ with respect to fertility and soil management groups, and how competing vegetation can be managed with operational treatments. Three separate multi-location long-term growth studies were examined from the vegetation management perspective.; Year 2 pine height response in a time-of-planting fertilization and first year herbaceous weed control study installed at twenty-four locations was examined using marginal response (response per unit of cover reduction) to account for variation in treatment efficacy. Pine response to weed control treatments was related more to quality of vegetation control than to fertilization regime, pine species, or soil management group, except for the lack of response without phosphorus fertilization on wet clay soils and limited response at several locations where drainage, poor bedding, and poor planting quality limited pine growth.; A study that examined the effects of woody shrub control and first year herbaceous control found that control of woody shrubs provided a larger age 8 pine response than control of herbaceous vegetation on spodosols with the effects being essentially additive. A modeling approach, using data pooled from four locations, determined that 87% of the variation in age 8 dominant pine height could be explained by initiation of vegetation control, first year herbaceous cover, first year untreated shrub cover, and fifth year shrub cover. The effect of vegetation on quadratic mean dbh and dbh percentiles could be explained by its effect on pine height and the negative effect of understory shrubs. These results were consistent across a wide range in site fertility for both loblolly and slash pine.; Finally, vegetation control and pine response were compared for early bed, late bed, double bed, banded pre-plant herbicide, and broadcast pre-plant herbicide site preparation with and without first year herbaceous control at four locations. Pre-plant herbicide treatments performed as well or better than all other treatments in terms of pine response while providing the most consistent vegetation control across four locations.