Live crown ratio model and lumber recovery for intensively managed loblolly pine

Loblolly pine is a commonly planted pine species in the Southern US which is intensively managed as well as a major contributor to the timber industry. Various silvicultural treatments are commonly applied to pine plantations including thinning and sometimes pruning. Tree crowns contain the active photosynthesis region and play a vital role in tree growth. Among various tree crown measurements, live crown ratio (LCR) is derived from height to live crown base (HLCB) and total tree height. Accurate measurement of HLCB is basis for live crown ratio prediction. Due to numerous definitions and practical considerations, HLCB and crown structure are difficult and slow to measure accurately. Despite this, LCR is a useful predictor in various growth and yield models. Due to the challenges in measuring tree crowns, accurate live crown ratio prediction models are useful. The LCR model of (Dyer and Burkhart, 1987) was refit with intensively managed plantation (IMP) data. The parameters were significant, and the residual plots showed no concerning patterns but the prediction of height to live crown base for pruned trees was not logical as it sometimes predicted HLCB lower than pruning height. To address this, the base model was modified to accommodate the pruning effect and provide logical predictions. LCR is in range of 0 - 1 and HLCB is greater or equal to pruning height. If trees are not pruned, it reverts to the original model. The models were validated with a dataset of IMP measurements not used in fitting. Validation statistics suggest the model performs nearly as well as the original, unconstrained base model. It is expected that the new model will be useful for forest managers to predict LCR of both pruned and unpruned trees. The second part of the study is to understand the importance of common tree variables in predicting the lumber recovery in planted loblolly pine. A random forest model was used to determine the variable importance of DBH, total tree height and live crown ratio for total board ft., high-grade, and high-grade lumber proportion compared to total board ft. DBH ranked at the first position followed by total tree height and live crown ratio similarly ranked for volume and high-grade lumber volume. For proportions of high-grade lumber, tree height was at top rank followed by LCR, and DBH. However, the effect of these variables for lumber recovery was not explored. It is suggested that future work can explore parametric model forms for accurately predicting lumber recovery using simple, easy to measure tree variables.