A model of ponderosa pine growth response to prescribed burning

Our objective was to model the radial growth response of individual ponderosa pines to prescribed burning in northern Arizona. We sampled 188 trees from two study areas, which were burned in 1976. Within each study area, control and burned trees were of similar age, vigor, height, and competition index. At Chimney Spring, trees were older, less vigorous, and taller and had a higher competition index than at Brannigan. For each tree, periodic basal area increment (PBAI) was calculated for the years 1974-1984. To determine which variable would best model growth, post-fire growth (1977-1984) was correlated with the 3 year average of previous growth, crown ratio, competition index, and diameter. Post-fire growth response was modeled using stepwise multiple linear regression as a function of previous growth and indicator variables for treatment, treatment-site interaction, climatic variation, and treatment-year interaction. Independent variables of the final model included previous growth, climatic variation, and treatment-year interaction (r² = 0.72). Model coefficients indicated that fire affected growth significantly and negatively for 2 years, and then burned trees grew similarly to control trees. differences in management history at the two sites did not affect growth after fire. We propose a linear aggregate model of variables controlling radial growth response of southwestern ponderosa pines to fire.