Productivity of natural stands of longleaf pine in relation to climatic factors

The effects of climate on long-term productivity of longleaf pine was examined. Regional longleaf pine growth and yield data were modeled at the stand level as well as at the individual tree level. A parameter stability analysis was performed using various subsets of data where the effects of stand dynamics have been accounted for or isolated as much as possible. Relationships between growth and climate variables were tested.; A likelihood ratio test indicated that model parameters changed significantly from one time period to the next. Further tests identified the particular parameters that were most sensitive to time and therefore in need of modification. The selection of a particular model or model form did not change the fact that model coefficients have changed significantly over the last 25 years.; Predicted parameters and residuals were highly correlated with various forms of the climatic variables and indices. Numerous combinations of climatic variables or indices were modeled and the particular combination that produced the least specification error was identified. Significant indices were identified for each climate variable (precipitation, minimum temperature, maximum temperature, and mean temperature), but a climatic index that included total precipitation and mean minimum temperature provided the best climate parameter for modeling basal area growth and yield. Sensitivity of the models to possible changes in climate were evaluated after including the climatic index. Results indicated 1.5-7% change in average basal area prediction with a 5% change in the climate variable. A comparison of model forms indicated that stand level basal area projection and basal area increment models were more sensitive to climate change than an individual tree model.; Results were consistent across several dependent variables and all models tested. To avoid inflated variance and bias in long-term projections, climate must be included in longleaf pine growth and yield models.