Influence of thinning and burning restoration treatments on presettlement ponderosa pines at the Gus Pearson Natural Area

This study assessed the effects of restoration treatments on growth, leaf physiology, and insect resistance characteristics of presettlement-age ponderosa pines (Pinus ponderosa Dougl. ex Laws.) at the Gus Pearson Natural Area in northern Arizona. Treatments (C, control; T, thinned from below; TB, thinned and prescribed burned) were designed to restore stand structure and disturbance regime to a pre-Euro-American settlement reference condition. Tree growth and some physiological characteristics differed between wet (1995) and dry (1996) years. Soil water content was greater in both thinned treatments than in the control. Compared with the control, trees in both thinned treatments had greater leaf nitrogen content (C = 1.44, T = 1.57, TB = 1.59 g·m^-2), leaf toughness (C = 65.1, T = 71.3, TB = 69.3 g), and basal area increment (C = 14.3, T = 19.9, TB = 20.7 cm²). Resin flow was greater in the thinned and burned treatment (12.2 mL·day^-1) than in the thinned treatment (4.3 mL·day^-1) and control (3.6 mL·day^-1). Treatment differences in predawn water potential and net photosynthetic rate varied among sample dates, with the largest differences during a period of drought (C < T and TB). Our results suggest that restoration treatments improved resource uptake, growth, and insect resistance capabilities of presettlement ponderosa pines.