Difference in Radial Growth Response to Restoration Thinning and Burning Treatments Between Young and Old Ponderosa Pine in Arizona

Thinning and burning treatments based on forest conditions present before Euro-American settlement have been proposed to improve growth of ponderosa pine (Pinus ponderosa) in northern Arizona. We examined tree growth response to different levels of such treatments and compared growth response between old trees that established before Euro-American settlement (presettlement trees) and younger trees that established after Euro-American settlement (postsettlement trees). We made these comparisons for 3 years of posttreatment growth in northern Arizona stands subjected to four levels of thinning. Thinning treatments varied the number of postsettlement trees retained to replace dead presettlement trees. Thinning increased radial growth at breast height of postsettlement trees in all 3 years after treatment, and growth response was negatively correlated with posttreatment stand basal area. In contrast, growth of presettlement trees was not affected by thinning in most years, and there was no relationship between growth and posttreatment stand basal area. Application of the same thinning prescription to stands with different management history resulted in different posttreatment basal area and consequently different growth response to thinning for postsettlement trees. Our results show that growth of 80-year-old, postsettlement ponderosa pines is more responsive to restoration thinning than older presettlement trees, and provide guidelines for thinning levels needed to stimulate growth of presettlement trees. West. J. Appl. For. 20(1):36–43.