Modeling trends in stem quality characteristics of loblolly pine trees in unthinned plantations

Abstract

Trends in stem quality characteristics of loblolly pine trees were investigated by using data from unthinned control plots established in plantations across 12 southern states in the United States and measured at 3 year intervals. At each measurement, the stem quality was classified into (i) single stem or forked, (ii) normal top or broken top, (iii) straight or sweep (bole sweep, butt sweep, short crook), and (iv) no disease or disease. Data through the first 15 years of observation showed that, on average, 4% of the trees were forked, 5% had broken tops, 41% had sweep, and 12% had disease or insect damage; 48% exhibited single stem, normal top, straight, and no disease or insect damage. Recovery rates out of forked, broken top, sweep, and disease classes were 37%, 83%, 30%, and 11%, respectively, over the 15 years. Multicategorical logit models were developed to predict stem quality characteristics from stand-and tree-level variables. Forked trees were related with tree diameter; broken tops were related with stand density, DBH, and relative height; sweep was related with stand age. Significant predictor variables for the incidence of disease or insect attack were not found. The occurrence of undamaged and disease-free trees can be predicted from DBH and relative height.