Accounting For Environmental Co-variables in Loblolly Pine (Pinus taeda L.) Diameter Distributions in the Western Gulf Physiographic Region of the United States

Diameter distribution modeling in loblolly pine (Pinus Taeda L.) plantations was conducted using the percentile estimation technique and the parameter recovery approach to evaluate the effects of silvicultural management intensity (fertilization and vegetation con trol) and environmental co-variables (precipitation, temperature, and water deficit) on the three-parameter Weibull distribution estimation. Data from the Plantation Management Research Cooperative in the Western Gulf Cultural Density trial established across three physiographic regions included five initial planting densities and two management regimes was used in this thesis. The results showed that with higher intensity of silvicultural manage ment the predicted percentiles were higher, and Weibull parameter was affected according to the level of silvicultural intensity and planting density, demonstrating their combined influ ence on stand structure. Incorporating environmental co-variables into the models influenced the Weibull three-parameter (location, shape, scale) and improved both model fit and the precision of parameter estimates compared to models without environmental co-variables.