General response functions to silvicultural treatments in loblolly pine plantations

Abstract

Forest growth and yield models that incorporate common silvicultural practices are essential for practicing intensive forest management. We present models for growth response to a wide range of silvicultural treatments in loblolly pine (Pinus taeda L.) plantations. Baseline models for basal area, dominant height, and survival were fitted using data from across the southeastern United States. Growth models for treated stands were developed by multiplying baseline models with modifier response functions accounting for effects of thinning, fertilization, and control of competing vegetation. Response to early control of competing vegetation was incorporated into baseline models through multiplier factors that were calculated from growth differences between treated and untreated stands. The thinning response function included duration and rate parameters and was sensitive to stand age at the time of thinning, time since thinning, and intensity of thinning. Fertilization response functions were based on the Weibull distribution; the magnitude of responses varies with time since application of fertilizers, type of fertilizer, and rate of application. A difference function, derived from a differential equation with age, initial stand density, and site index as predictors, served as the baseline survival model. The survival model was adjusted for thinning treatment by including an additional independent variable that represents thinning intensity. The resulting models were able to predict growth response when single, as well as multiple, treatments were applied.